The first EMEP intensive measurement periods were held in June 2006 and January 2007. The measurements aimed to characterize the aerosol chemical compositions, including the gas/aerosol partitioning of inorganic compounds. The measurement program during these periods included daily or hourly measurements of the secondary inorganic components, with additional measurements of elemental- and organic carbon (EC and OC) and mineral dust in PM1, PM2.5 and PM10. These measurements have provided extended knowledge regarding the composition of particulate matter and the temporal and spatial variability of PM, as well as an extended database for the assessment of chemical transport models. This paper summarise the first experiences of making use of measurements from the first EMEP intensive measurement periods along with EMEP model results from the updated model version to characterise aerosol composition. We investigated how the PM chemical composition varies between the summer and the winter month and geographically. The observation and model data are in general agreement regarding the main features of PM10 and PM2.5 composition and the relative contribution of different components, though the EMEP model tends to give slightly lower estimates of PM10 and PM2.5 compared to measurements. The intensive measurement data has identified areas where improvements are needed. Hourly concurrent measurements of gaseous and particulate components for the first time facilitated testing of modelled diurnal variability of the gas/aerosol partitioning of nitrogen species. In general, the modelled diurnal cycles of nitrate and ammonium aerosols are in fair agreement with the measurements, but the diurnal variability of ammonia is not well captured. The largest differences between model and observations of aerosol mass are seen in Italy during winter, which to a large extent may be explained by an underestimation of residential wood burning sources. It should be noted that both primary and secondary OC has been included in the calculations for the first time, showing promising results. Mineral dust is important, especially in southern Europe, and the model seems to capture the dust episodes well. The lack of measurements of mineral dust hampers the possibility for model evaluation for this highly uncertain PM component. There are also lessons learnt regarding improved measurements for future intensive periods. There is a need for increased comparability between the measurements at different sites. For the nitrogen compounds it is clear that more measurements using artefact free methods based on continuous measurement methods and/or denuders are needed. For EC/OC, a reference methodology (both in field and laboratory) was lacking during these periods giving problems with comparability, though measurement protocols have recently been established and these should be followed by the Parties to the EMEP Protocol. For measurements with no defined protocols, it might be a good solution to use centralised laboratories to ensure comparability across the network. To cope with the introduction of these new measurements, new reporting guidelines have been developed to ensure that all proper information about the methodologies and data quality is given.

A unique long-term (1983-2013) dataset of sulfur and nitrogen deposition has been compiled for Sweden as well as the Baltic Sea and surrounding countries, based on quality controlled measurements and modelled fields, fused though advanced methods capturing spatial and temporal variations. The data set can be used for describing trends in deposition to various relevant surface types.Our reanalysis compares well to observations, but we have identified differences in dry deposition to coniferous forest. This calls for more in-depth studies of the dry deposition and improvements to the respective methods.We recommend more advanced methods of describing spatial variation than averaging or spatial interpolation of observed deposition.We estimate a significant decrease from the 1980s until today for both sulfur and nitrogen deposition (by ca. 80% and 30% respectively).Critical loads for coniferous and deciduous forests, mountain vegetation and wetlands have been surpassed mainly in the southwest Sweden, but also in southeast Sweden and the southern parts of Scandes Mountains. The situation is improving, but exceedances do still occur also in larger regions.

I denna studie presenteras nutid (2010) och förändring till framtid (2020) för ett emissionsscenario baserat på PRIMES energimodell och IMO-beslut för internationell sjöfart. Utifrån dessa uppskattningar har modellberäkningar gjorts över nutid och förändring till 2020 för deposition av kväve och svavel, samt för lufthalter av sekundära inorganiska aerosoler (SIA; partiklar) och marknära ozon. Bidrag och förändring i detta bidrag till 2020 har presenterats för internationell sjöfart. Även Sveriges och övriga Europas bidrag till deposition i nutid och förändring till framtid har presenterats.Huvudresultaten i studien är:- Landbaserade utsläpp av svaveldioxid, kväveoxider, partiklar, kolmonoxid och volatila organiska ämnen förväntas minska i Europa såväl som i Sverige, medan utsläppen av ammoniak förväntas öka till 2020 i Europa.- Internationell sjöfart förväntas minska sina utsläpp av svaveldioxid på grund av IMO-beslut, men förväntad ökning i trafiken medför ökade utsläpp av NOx.- Såväl deposition som lufthalter fortsätter vara högst i södra Sverige.- Utsläppsminskningarna till 2020 medför minskat nedfall av svavel och kväve i Sverige.- Bidraget till kvävedeposition från internationell sjöfart ökar i hela landet till 2020, övriga bidrag minskar.- Luftkvaliteten i regional bakgrundsluft i Sverige förbättras för såväl marknära ozon som för SIA.- De högsta halterna av marknära ozon beräknas minska som en följd av utsläppsminskningar i Europa.

We have implemented the sectional aerosol dynamics model SALSA (Sectional Aerosol module for Large Scale Applications) in the European-scale chemistry-transport model MATCH (Multi-scale Atmospheric Transport and Chemistry). The new model is called MATCH-SALSA. It includes aerosol microphysics, with several formulations for nucleation, wet scavenging and condensation. The model reproduces observed higher particle number concentration (PNC) in central Europe and lower concentrations in remote regions. The modeled PNC size distribution peak occurs at the same or smaller particle size as the observed peak at four measurement sites spread across Europe. Total PNC is underestimated at northern and central European sites and accumulation-mode PNC is underestimated at all investigated sites. The low nucleation rate coefficient used in this study is an important reason for the underestimation. On the other hand, the model performs well for particle mass (including secondary inorganic aerosol components), while elemental and organic carbon concentrations are underestimated at many of the sites. Further development is needed, primarily for treatment of secondary organic aerosol, in terms of biogenic emissions and chemical transformation. Updating the biogenic secondary organic aerosol (SOA) scheme will likely have a large impact on modeled PM2.5 and also affect the model performance for PNC through impacts on nucleation and condensation.

This report presents a new aerosol dynamics version of a European scale Eulerian CTM, MATCH. The new model is called MATCH-SALSA, and includes aerosol microphysics and several options for nucleation, wet scavenging and condensation. The report entails model description, evaluation and sensitivity tests.The new model reproduces observed higher particle number concentration (PNC) in central Europe and lower in remote regions. The model peak PNC occurs at the same particle size as the observed peak or at smaller sizes, which indicate missing growth. Total PNC is underestimated at some sites. The model performs well for particle mass, including SIA components. EC and OC are underestimated at many of the sites.The results are sensitive to the fraction of SOx emitted as H2SO4 and the optimum choice is site dependent. The model results are highly sensitive to whether organic nucleation is included or not. The model results are sensitive to amount of organic vapors in the condensation. The model can be used in applications knowing the restrictions of what the model manages well and what needs further improvements, which is detailed in the report.

This paper presents the contribution to population exposure (PE) of regional background fine primary (PPM(2.5)) and secondary inorganic (SIA) particulate matter and its impact on mortality in Europe during 1997-2003 calculated with a chemistry transport model. Contributions to concentrations and PE due to emissions from shipping, Western (WEU), Eastern (EEU), and Northern Europe are compared. WEU contributes about 40% to both PPM(2.5) and SIA concentrations, whereas the EEU contribution to PPM(2.5) is much higher (43% of total PPM(2.5)) than to SIA (29% of total SIA). The population weighted average concentration (PWC) of PPM(2.5) is a factor of 2.3 higher than average (non-weighted) concentrations, whereas for SIA the PWC is only a factor 1.6 higher. This is due to PPM(2.5) concentrations having larger gradients and being relatively high over densely populated areas, whereas SIA is formed outside populated areas. WEU emissions contribute relatively more than EEU to PWC and mortality due to both PPM(2.5) and SIA in Europe. The number of premature deaths in Europe is estimated to 301000 per year due to PPM(2.5) exposure and 245 000 due to SIA, despite 3.3 times higher average SIA concentrations. This is due to population weighting and assumed (and uncertain) higher relative risk of mortality for PPM(2.5) components (2.8 times higher RR for PPM(2.5)). This study indicates that it might be more efficient, for the health of the European population, to decrease primary PM emissions (especially in WEU) than to decrease precursors of SIA, but more knowledge on the toxicity of different PM constituents is needed before firm conclusions can be drawn. (C) 2009 Elsevier Ltd. All rights reserved.

Projections of future surface ozone over Europe conducted utilizing chemistry transport models (CTMs) coupled to climate models differ greatly, even in sign. CTM sensitivity studies were conducted in order to investigate the importance of changes in natural isoprene emissions and dry deposition to vegetation, both coupled to meteorology. This knowledge can be used to improve surface ozone projections. Our simulations suggest climate change over Europe would cause changes in surface ozone between -4.0 to +13 ppb(v) on average (April-September) and -3.5 to +25 ppb(v) on average (April-September) daily maximum from 1961 - 1990 to 2071 - 2100. The change is positive in the southwest and negative in the north. The isoprene emissions increased by a factor of about 1.8 from 1961 - 1990 to 2071 - 2100. A rescaling of isoprene emissions shows that the large increase in isoprene emission is of importance (0 - 30% of the change in surface ozone) in central, southern, and western Europe. The use of a formulation for ozone dry deposition to vegetation, dependent on meteorology, and changes in snow cover, affecting the dry deposition, are more important processes. The changes in dry deposition to vegetation (not including changes in aerodynamic resistance) explain up to 80% of the surface ozone change in Spain. Therefore it is vital to include meteorological dependence for dry deposition of ozone to vegetation in surface ozone projections. Isoprene emissions are of less importance, but they are nonnegligible and should definitely be emitted online in climate ozone projection studies.

A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of surface ozone (O(3)), nitrogen dioxide (NO(2)) and particulate matter (PM) and its constituents over Europe during 1958-2001. The model was coupled to the meteorological reanalysis ERA40, produced at the European Centre for Medium-range Weather Forecasts. Emissions and boundary conditions of chemical compounds and PM were kept constant at present levels. The average European interannual variation, due to meteorological variability, ranges from 3% for O(3), 5% for NO(2), 9% for PM, 6-9% for dry deposition, to about 20% for wet deposition of sulphur and nitrogen. For the period 1979-2001 the trend in ozone, due to climate variability is increasing in central and southwestern Europe and decreasing in northeastern Europe, the trend in NO(2) is approximately opposite. The trend in PM is positive in eastern Europe. There are negative trends in wet deposition in southwestern and central Europe and positive trends in dry deposition overall. A bias in ERA40 precipitation could be partly responsible for the trends. The variation and trends need to be considered when interpreting measurements and designing measurement campaigns.

Hemispheric transport of air pollutants can have a significant impact on regional air quality, as well as on the effect of air pollutants on regional climate. An accurate representation of hemispheric transport in regional chemical transport models (CTMs) depends on the specification of the lateral boundary conditions (LBCs). This study focuses on the methodology for evaluating LBCs of two moderately long-lived trace gases, carbon monoxide (CO) and ozone (O-3), for the European model domain and over a 7-year period, 2006-2012. The method is based on combining the use of satellite observations at the lateral boundary with the use of both satellite and in situ ground observations within the model domain. The LBCs are generated by the global European Monitoring and Evaluation Programme Meteorological Synthesizing Centre - West (EMEP MSC-W) model; they are evaluated at the lateral boundaries by comparison with satellite observations of the Terra-MOPITT (Measurements Of Pollution In The Troposphere) sensor (CO) and the Aura-OMI (Ozone Monitoring Instrument) sensor (O-3). The LBCs from the global model lie well within the satellite uncertainties for both CO and O-3. The biases increase below 700 hPa for both species. However, the satellite retrievals below this height are strongly influenced by the a priori data; hence, they are less reliable than at, e.g. 500 hPa. CO is, on average, underestimated by the global model, while O-3 tends to be overestimated during winter, and underestimated during summer. A regional CTM is run with (a) the validated monthly climatological LBCs from the global model; (b) dynamical LBCs from the global model; and (c) constant LBCs based on in situ ground observations near the domain boundary. The results are validated against independent satellite retrievals from the Aqua-AIRS (Atmospheric InfraRed Sounder) sensor at 500 hPa, and against in situ ground observations from the Global Atmospheric Watch (GAW) network. It is found that (i) the use of LBCs from the global model gives reliable in-domain results for O-3 and CO at 500 hPa. Taking AIRS retrievals as a reference, the use of these LBCs substantially improves spatial pattern correlations in the free troposphere as compared to results obtained with fixed LBCs based on ground observations. Also, the magnitude of the bias is reduced by the new LBCs for both trace gases. This demonstrates that the validation methodology based on using satellite observations at the domain boundary is sufficiently robust in the free troposphere. (ii) The impact of the LBCs on ground concentrations is significant only at locations in close proximity to the domain boundary. As the satellite data near the ground mainly reflect the a priori estimate used in the retrieval procedure, they are of little use for evaluating the effect of LBCs on ground concentrations. Rather, the evaluation of ground-level concentrations needs to rely on in situ ground observations. (iii) The improvements of dynamic over climatological LBCs become most apparent when using accumulated ozone over threshold 40 ppb (AOT40) as a metric. Also, when focusing on ground observations taken near the inflow boundary of the model domain, one finds that the use of dynamical LBCs yields a more accurate representation of the seasonal variation, as well as of the variability of the trace gas concentrations on shorter timescales.

A new aerosol-optics model is implemented in which realistic morphologies and mixing states are assumed, especially for black carbon particles. The model includes both external and internal mixing of all chemical species, it treats externally mixed black carbon as fractal aggregates, and it accounts for inhomogeneous internal mixing of black carbon by use of a novel "core-grey-shell" model. Simulated results of aerosol optical properties, such as aerosol optical depth, backscattering coefficients and the Angstrom exponent, as well as radiative fluxes are computed with the new optics model and compared with results from an older optics-model version that treats all particles as externally mixed homogeneous spheres. The results show that using a more detailed description of particle morphology and mixing state impacts the aerosol optical properties to a degree of the same order of magnitude as the effects of aerosol-microphysical processes. For instance, the aerosol optical depth computed for two cases in 2007 shows a relative difference between the two optics models that varies over the European region between 28 and 18 %, while the differences caused by the inclusion or omission of the aerosol-microphysical processes range from 50 to 37 %. This is an important finding, suggesting that a simple optics model coupled to a chemical transport model can introduce considerable errors affecting radiative fluxes in chemistry-climate models, compromising comparisons of model results with remote sensing observations of aerosols, and impeding the assimilation of satellite products for aerosols into chemical-transport models.

Den här studien är en kartläggning och screening av emissioner och halter av benso(a)pyren (B(a)P) i Sverige. Syftet är att identifiera potentiella riskområden för överskridande av miljökvalitetsnormen (MKN). Ett övervägande bidrag till haltnivåerna till B(a)P är emissioner från den småskaliga vedeldningen, varför studien går ut på att beräkna och fördela emissionerna från uppvärmning av småhus. Metodiken består översiktligt av tre delar; beräkning av kommunvisa emissioner av B(a)P i Sverige, fördelning av dessa årsemissioner inom kommunerna på ett raster om 1 km × 1 km samt beräkning av årsmedelhalter utifrån detta emissionsraster. För att beräkna kommunvisa årsemissioner av B(a)P utnyttjas statistik från MSB över antalet eldstäder, modellerade värden på småhusens energibehov från ENLOSS, antaganden om eldvanor och emissionsfaktorer per typ av eldstad. De kommunvisa emissionerna fördelas sedan inom kommunen i ett grid om 1 km × 1 km utgående från antal kvadratmeter boyta småhus per km2 från fastighetsregistret. För pannor används dessutom tätortsvis statistik från Energimarknadsinspektionen över antal anslutna småhus till fjärrvärmenät, som vi enligt egen fördelning applicerar tätortsvis. Slutligen beräknas årsmedelhalter av B(a)P utifrån emissionsrastret på 1 km × 1 km utgående från linjära samband mellan emissioner och halter från tidigare genomförda lokalskaliga spridningsberäkningar med SIMAIR-ved i Västerbottenprojektet. Huvudslutsatserna från studien är följande: • De högsta årsemissionerna av B(a)P från vedpannor, som står för i särklass högst emission per enhet och därmed har störst påverkan på den lokala luftkvaliteten, beräknas för Skellefteå (18 200 g år–1) följt av Örnsköldsvik (13 600 g år–1), Gotland (13 500 g år–1), Sundsvall (12 900 g år–1) och Hudiksvall (12 300 g år–1). • Utifrån ett linjärt antagande mellan emissioner och halter fås kommunvisa årsmedelhalter av B(a)P 2012 på 0.03 – 1.03 ng m–3 för haltmåttet kartans högsta värde (KHV). Motsvarande värden för kartans ytmedelvärde (KYM) är 0.01 – 0.25 ng m–3. • Beräkningarna indikerar att det föreligger risk för överskridande av MKN (>1.0 ng m–3) i vissa enskilda gridrutor i tätorterna Sollefteå och Laholm (avseende årsmedelhalt av B(a)P uttryckt som KHV). Höga årsmedelhalter (>0.8 ng m–3) fås även för Kramfors, Säffle, Arvidsjaur, Boden, Skellefteå och Trollhättan. Detta är kommuner med en stor andel vedpannor i förhållande till lokaleldstäder. • Merparten (273 av 290) av kommunerna i Sverige har haltnivåer (KHV) högre än miljökvalitetsmålet Frisk luft (>0.1 ng m–3). Här är påverkan även betydande för utsläpp från trivseleldning med lokaleldstäder. • Studien ska ses som en översiktlig kartläggning och screening av emissioner och halter av B(a)P från småskaliga vedeldningen. Beräkningarna kan anses representera ett ”worst case”. • Den i särklass största osäkerheten vad gäller indata är statistiken från MSB över antalet eldstäder per kommun, samt hur eldstäderna fördelas mellan olika kommuner i gemensamma räddningstjänstområden. Detaljeringsgraden av underlaget samt klassificeringen av eldstäderna kan variera betydligt mellan olika kommuner/räddningstjänstförbund. För kommuner som enligt beräkningarna har haltnivåer som överskrider eller är nära att överskrida MKN rekommenderas, i ett första steg, att en noggrannare granskning/inventering görs av indata som används i beräkningarna, i synnerhet antalet eldstäder. In this report methods and results are presented from downscaling of about 40 climate

I det nya EU-direktivet för luftkvalitet definieras ett exponeringskoncentrationstak för PM2.5. Detta takvärde, som inte får överskridas efter år 2015, är satt till 20 μg/m3 som årsmedelvärde. Eftersom även lägre halter påverkar människors hälsa negativt införs även ett exponeringsminskningsmål av partikelhalter i urban bakgrund. Hur stort exponeringsminskningsmålet blir för en viss plats beror på PM2.5-halterna vid referensåret 2010. Högre halt kräver högre relativ reducering till år 2020. I denna studie utreds det nya direktivets betydelse för Sverige. Utgångsläget kartläggs genom analys av mätdata av PM2.5 för ett antal platser runt om i Sverige. Olika emissionsscenarier tillämpas för att undersöka hur den regionala PM2.5-halten och långdistansbidraget kan komma att ändras från nuläget till år 2020 genom simuleringar med spridningsmodellen MATCH. Då det gäller det lokala haltbidragets betydelse för totalhalten av PM2.5 i nuläget respektive för år 2020, undersöks detta genom beräkningar i SIMAIR, för olika emissionsscenarier som innefattar dubbdäcksanvändning, teknikutveckling och trafikökning. Mätdata har sammanställts och analyserats för 25 mätplatser, varav 4 regionala bakgrundsstationer, 8 urbana bakgrundsstationer samt 13 mätstationeri gaturum. Uppmätta årsmedelvärden av PM2.5 ligger i gaturum generellt i intervallet 10-18 μg/m3 medan motsvarande värden för urban bakgrundoch regional bakgrund är 9-12 μg/m3 respektive 6-12 μg/m3. Halterna av PM2.5 underskrider 20 μg/m3 för samtliga platser och år, vilket betyder attexponeringskoncentrationstaket redan i dagsläget är uppfyllt. Den relativa skillnaden mellan halter i gaturum och regional bakgrundsluft är betydligtmindre för PM2.5 än för PM10, vilket indikerar att merparten av de fina partiklarna i gaturum härstammar från långdistanskällor. Liksom för PM10observeras också för PM2.5 ett maximum på våren, vilket tyder på att en del av partiklarna från vägslitage och uppvirvling är fina. Långdistanstransporten från kontinentaleuropa leder till en nord-sydlig gradient av PM2.5 i regionala bakgrundsluften. Däremot kan inte någotentydigt latitudberoende observeras för gaturum.För att uppskatta möjliga reduceringar av årsmedelhalten av PM2.5 från år 2010 till år 2020 har modellsimuleringar utförts med den regionalaspridningsmodellen MATCH. Tre olika europeiska emissionsscenarier för 2020 har studerats (CLECLIM, D23LOW och MFRDEEP). Beräkningsresultaten ger reduceringar som uppgår till 1.0-2.5 μg/m3 i södra Sverige och 0.1-0.5 μg/m3 i norra Sverige, för ett troligt emissionsscenario (D23LOW). Utsikterna att uppnå målet 10% minskning av PM2.5-halterna i södra Sverige bedöms därför som goda. Beräkningarna visar också att långdistanstransporten är det dominerande bidraget till PM2.5 i regional bakgrundsluft i Sverige. Slutligen konstateras att för regionala bakgrundshalter av PM2.5 är påverkan från vägtrafikens slitagepartiklar liten. Bibehållen dubbdäcksanvänding år 2020 beräknas geen obetydlig ökning av fina slitagepartiklar i den regionala bakgrundsluften (maximalt ca 0.02 μg/m3) pga ökat trafikarbete, medan minskad användning av dubbdäck kan leda till en liten reducering av halterna till år 2020 (upp till ca 0.1 μg/m3 för scenariot utan dubbdäck). För halter i urbanbakgrundsluft förväntas påverkan vara något större än den som beräknats här.För att beräkna det lokala bidraget till PM2.5 har uppskattningar av totala emissionsfaktorer för PM2.5 gjorts. Uppskattningarna baserades på tidigarestudier med mätdata av hög kvalitet från gaturum i Sverige, Danmark och Tyskland samt modellberäkningar med hjälp av SIMAIRs emissionsmodellför slitagepartiklar. Utgående ifrån emissionsfaktorerna beräknades lokala haltbidrag i gaturummen med SIMAIR för 4 olika emissionsscenarier; (1)nuläge motsvarande år 2004, (2) år 2020 utan förändringar vad gäller dubbdäcksanvändning, (3) år 2020 andelar dubbdäck i hela landet är 30 % samt (4) år 2020 utan dubbdäck. Beräkningarna för dessa scenarier indikerar att under nuvarande förhållanden är det lokala haltbidraget av PM2.5 ca 6 μg/m3 i Stockholm/Hornsgatan, ca 4 μg/m3 i Umeå/Västra Esplanaden och ca 2.5-3 μg/m3 för Göteborg/Gårda och Malmö/Amiralsgatan.Teknikutveckling till år 2020 (scenario 2) minskar lokala haltbidrag med 1.3-2.3 μg/m3 och mindre dubbdäcksanvändning (scenario 3) reducerarhalterna med ytterligare 1-3 μg/m3 i främst Stockholm och Umeå. Däremot blir de beräknade halterna bara marginellt lägre i scenariot helt utandubbdäck jämfört med 30% dubbdäcksanvändning. Detta kan förklaras med att en gata, HC Andersens Boulevard i Köpenhamn, med högemissionsfaktor för uppvirvlingen av vägdamm, har använts som referensgata.

SIMAIR är ett webbaserat modellsystem för beräkning av luftkvalitet i svenska tätorter. Systemet är utvecklat av SMHI på uppdrag av Trafikverket, Naturvårdsverket och Energimyndigheten och syftar till att tillhandahålla svenska kommuner och andra aktörer ett lättanvänt verktyg som kan användas i luftvårdsarbetet, bland annat för att bedöma luftföroreningsnivåerna i relation till miljökvalitetsnormer och utvärdera olika åtgärders effekter på luftmiljön. Syftet med denna studie är att utvärdera SIMAIR mot nya mätdata av PM10 och NO2 och testa och utvärdera en ny emissionsmodell för vägtrafikens slitagepartiklar.Högkvalitativa mätningar med timupplösning från tre trafikmiljöer har använts i utvärderingen; E6 vid Gårda i Göteborg för åren 2006-2009, Hornsgatan i Stockholm för åren 2007-2009 samt Västra Esplanaden i Umeå för åren 2006-2009. Modellens beräkningar i urban bakgrund (regionalt + urbant bidrag) har även utvärderats mot mätningar i urban bakgrund (i taknivå) för dessa tätorter; Femman-huset i Göteborg, Torkel Knutssonsgatan i Stockholm samt Biblioteket i Umeå. I utvärderingen används ett antal statistiska mått och indikatorer för att kvantifiera modellens prestanda i jämförelse med mätdata. Bland annat jämförs årsmedelvärden, percentiler, antalet överskridanden, bias, korrelationskoefficient och Target. I valideringen har ett nytt utvärderingsverktyg använts, Delta-tool, utvecklat inom ramen för det europeiska initiativet FAIRMODE.Utvärderingen av SIMAIR visar att i trafikmiljöer underskattas PM10-halterna något för Hornsgatan i Stockholm (med ca 20-30 %). För Västra Esplanden i Umeå och i synnerhet E6 vid Gårda i Göteborgöverskattas istället PM10-halterna (med 10-35 %). Däremot, i urban bakgrund är överensstämmelsen mellan modellerade och uppmätta PM10-halter genomgående mycket god.En systematisk underskattning av NO2-halterna kan observeras både i trafikmiljöer (generellt 10-30 %) och urban bakgrund (generellt 10-30 %) jämfört med mätdata (bortsett från urban bakgrund i Stockholmdär modellen uppvisar god överenstämmelse med mätdata). Trots att det finns ett viss bias för NO2 är resultaten ändå goda; 75 % av datapunkterna har ett lägre targetvärde än 1, vilket betyder att modellen då kan vara en bättre prediktor för atmosfärens ”verkliga” kemiska tillstånd än mätningarna.Denna studie tillsammans med tidigare valideringsstudie av SIMAIR visar att modellen uppfyller kvalitetsmålen på modellberäkningar (RPE/RDE) för såväl PM10 och NO2 i trafikmiljöer.Inom ramen för ett nordiskt forskningsprojekt har en ny emissionsmodell för vägdamm utvecklats; NORTRIP. Modellen bygger delvis på samma principer som SIMAIRs vägdammsmodell, men viktiga förbättringar har gjorts. Syftet med denna undersökning är att analysera förutsättningarna för att använda NORTRIP med hjälp av indata från SIMAIR. Undersökningen visar att det är möjligt, men att det finns en del svårigheter.NORTRIP-modellen ger något högre korrelation mot mätdata jämfört med SIMAIRs vägdammsmodell. Med övriga indata från SIMAIR för år 2007 ökar korrelationen från 0.58 till 0.67 för Västra Esplanaden,från 0.59 till 0.67 för Hornsgatan och från 0.53 till 0.57 för Gårda. För att få överensstämmande haltnivåer behövs dock korrektioner införas; korrektioner som för närvarande inte är lätta att förstå. Det är inte säkert att den standardparameteruppsättning, som tagits fram baserat på mätningar från två gator i Stockholm, är så generell att den också kan tillämpas för andra trafikmiljöer i Sverige.Ett enkelt sätt att förbättra SIMAIRs beräkningsresultat är att korrigera dessa mot mätdata. För att förbättra modellresultaten utan användandet av mätdata krävs förbättrade emissioner, vilket sannoliktkommer göras inom ramen för HBEFA i Europa, samt att implementera NORTRIP-modellen. Innan NORTRIP-modellen kan implementeras i SIMAIR behövs emellertid fler studier avseende vilka parametervärden och korrektioner som ska användas.

I denna studie har SIMAIR (med SIMAIR avses i denna rapport SIMAIRväg) validerats mot mätningar av PM10, NO2 och bensen för 19 mätstationer i gaturum och 21 mätstationer i urban bakgrund. Trafikmiljöerna är av skiftande karaktär och från olika delar av Sverige. Mätstationerna i urban bakgrund är samtliga belägna vid en central plats i respektive tätort, men placeringen varierar (både mätningar vid torg och gågator samt takmätningar förekommer). Vid valideringen jämförs ett antal statistiska mått för att kvantifiera överensstämmelsen mellan uppmätta och beräknade halter. I EUs Luftdirektiv finns kvalitetsmått angivna, som fastställer maximalt acceptabel osäkerhet för modellberäkningar. Den bästa tolkningen av denna osäkerhet är begreppet RPEmax, det maximala relativa percentilfelet för 90% av stationerna, vilket är kvalitetsmåttet som tillämpas i denna studie. Utöver detta mått används även medianen för RPE (RPEmedian), vilket ur modelleringssynpunkt kanske är mer intressant. Andra statistiska mått som utvärderas är uppmätta och beräknade årsmedelvärden, percentiler för dygns- och timmedelvärden, variationskoefficient (CoV) och korrelationskoefficient (r). Där signalen är stark, det vill säga i trafikerade gaturum, är överensstämmelsen mellan uppmätta och beräknade halter god. För PM10 och NO2 klaras EUs kvalitetskrav med tämligen stor marginal, men för bensen överskattar dock SIMAIR halterna systematiskt ijämförelse med mätdata. För urban bakgrund är resultatet relativt bra för många stationer. EUs kvalitetskrav för PM10 klaras, men för NO2 underskattas halterna. Vad gäller bensen i urban bakgrund överskrids kvalitetskravet marginellt. Emellertid är resultaten bättre än för gaturum. Korrelationen är överlag tämligen stark för de flesta platser och SIMAIR återger representativ säsongsvariation av halterna.Att halterna av NO2 underskattas i den urbana bakgrunden kan delvis förklaras med att mätningar ofta representerar halter i punkter medan modellen representerar halter i kilometerrutor. Ur valideringssynpunkt är urbana mätstationer i taknivå lämpligast att göra jämförelser mot, då det finns viss risk att lokal haltpåverkan får genomslag i mätningar vid exempelvis öppna torg och gågator. En annan förklaring till att halterna i urban bakgrund underskattas är att SIMAIRs urbana modell, BUM, har brister i beskrivningen av stabila atmosfäriska förhållanden, vilket delvis kan förklara den stora underskattningen av halter av NO2 i norra Sverige. Parametriseringen vid stabila förhållanden behöver förbättras, vilket är ett arbete som har påbörjats. För tillfället används en statistisk metod för att korrigera detta, kallad klimatkorrigering, och denna metod visar sig förbättra modellberäkningarna för flertalet platser i Norrland. För Sandviken leder klimatkorrigering dock till att de beräknade halterna blir avsevärt högre än de uppmätta och här blir RPE större än innan. Den geografiska gränsen mellan var klimatkorrigering är lämplig och inte är således inte helt klar. För höga emissionsfaktorer för vägtrafikens utsläpp av bensen kan troligtvis förklara överskattningen som sker för beräkningarna i gaturum av bensenhalter. Denna del behöver granskas och uppdateras.

The urban background dispersion model, BUM, used in the SIMAIR-system, is a simple trajectory model for evaluation of Air Quality in urban areas on 1 x 1 km spatial resolution. The urban contribution to concentrations in a receptor point is calculated from the emission sources in an upstream influence area whose size is dependent on the wind speed. This simple and attractive concept enables fast model calculations and the model is applied for more than 100 Swedish towns within SIMAIR. However, comparison with measured concentrations has shown that BUM underestimates levels of NO2 and NOX, especially for towns in northern Sweden. The reason for this is probably meteorological, i.e. it exemplifies the difficulties in describing the dispersion of air pollutants during strong stable atmospheric conditions. This problem has previously been solved by a statistical method (regression analysis), to adjust the calculations against measurements for towns in northern Sweden. The result of this method has varied widely; for some urban areas the result has been good while the correlation between measured and calculated concentrations has been lower for others. The aim of this study is, through a sensitivity analysis, to examine the parameters of the model that most significantly affect the levels of NO2, and subsequently improve the parametrization of these during stable atmospheric conditions. Furthermore, the results are validated against measurements from 13 urban areas in Sweden. According to the sensitivity analysis, it is the parametrization of the vertical dispersion parameter σz that most affects the levels of NO2. A new parametrization, which takes into account the stability, is introduced for urban areas outside major cities. This generally raises the concentrations with several μgm-3 on annual basis and 10’s μgm-3 for 98-percentile daily mean concentration. Furthermore, a correction of the meteorology (from Mesan) is introduced used in the calculations of BUM, for the meteorology to represent more urban (rough) conditions. The improvements of BUM lead to a better consistency between the model and the measurements. Generally, the correlation between the calculated and the measured concentrations of NO2 increases, and the time variation of concentrations is better captured in the model. Annual averages, and especially 98-percentile daily- and hourly mean value, are better reproduced in the improved version of BUM; when compared to measured concentrations, 37 % of data points are within ± 50 % for the original BUM while the corresponding results for the new BUM is 95 %. However, the new BUM model still doesn’t succeed, for all towns in northern Sweden, to fully reproduce the highest daily and hourly peaks of concentrations. In comparison with the original BUM climate corrected concentrations (in northern Sweden), the correlation between calculated and measured concentrations is higher for the new BUM, especially in terms of annual average, correlation coefficient and coefficient of variation.

We have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at high latitudes (>50 degrees N) in July 2008, using 10 global chemical transport model simulations from the POLMIP multimodel comparison exercise. In model air masses dominated by fire emissions, Delta O-3/Delta CO values ranged between 0.039 and 0.196 ppbv ppbv(-1) (mean: 0.113 ppbv ppbv(-1)) in freshly fire-influenced air, and between 0.140 and 0.261 ppbv ppb(-1) (mean: 0.193 ppbv) in more aged fire-influenced air. These values are in broad agreement with the range of observational estimates from the literature. Model Delta PAN/Delta CO enhancement ratios show distinct groupings according to the meteorological data used to drive the models. ECMWF-forced models produce larger Delta PAN/Delta CO values (4.47 to 7.00 pptv ppbv(-1)) than GEOS5-forced models (1.87 to 3.28 pptv ppbv(-1)), which we show is likely linked to differences in efficiency of vertical transport during poleward export from mid-latitude source regions. Simulations of a large plume of biomass burning and anthropogenic emissions exported from towards the Arctic using a Lagrangian chemical transport model show that 4-day net ozone change in the plume is sensitive to differences in plume chemical composition and plume vertical position among the POLMIP models. In particular, Arctic ozone evolution in the plume is highly sensitive to initial concentrations of PAN, as well as oxygenated VOCs (acetone, acetaldehyde), due to their role in producing the peroxyacetyl radical PAN precursor. Vertical displacement is also important due to its effects on the stability of PAN, and subsequent effect on NOx abundance. In plumes where net ozone production is limited, we find that the lifetime of ozone in the plume is sensitive to hydrogen peroxide loading, due to the production of HOx from peroxide photolysis, and the key role of HO2 + O-3 in controlling ozone loss. Overall, our results suggest that emissions from biomass burning lead to large-scale photochemical enhancement in high-latitude tropospheric ozone during summer.

Over the last two decades a number of heatwaves have brought the need for heatwave early warning systems (HEWS) to the attention of many European governments. The HEWS in Europe are operating under the assumption that there is a high correlation between observed and forecasted temperatures. We investigated the sensitivity of different temperature mortality relationships when using forecast temperatures. We modelled mortality in Stockholm using observed temperatures and made predictions using forecast temperatures from the European Centre for Medium-range Weather Forecasts to assess the sensitivity. We found that the forecast will alter the expected future risk differently for different temperature mortality relationships. The more complex models seemed more sensitive to inaccurate forecasts. Despite the difference between models, there was a high agreement between models when identifying risk-days. We find that considerations of the accuracy in temperature forecasts should be part of the design of a HEWS. Currently operating HEWS do evaluate their predictive performance; this information should also be part of the evaluation of the epidemiological models that are the foundation in the HEWS. The most accurate description of the relationship between high temperature and mortality might not be the most suitable or practical when incorporated into a HEWS.

As part of the model intercomparison study MICS Asia II, the Swedish MATCH model was set up for Southeast and East Asia. In that study, the comprehensive photochemistry scheme of MATCH was used for the first time in Asia. The current work focuses on results of surface ozone from the MATCH model simulations falling outside the model intercomparison study. Model results of surface ozone concentrations for the entire year of 2001 were investigated and compared with measurements in Southeast Asia. The model produced higher surface ozone concentrations than the observations at all of the non-remote stations investigated but underestimated during the dry season at remote locations. Modelled seasonal variation was similar to, but less pronounced than, the variation in the measurements. This study indicates that NO(x) is the limiting precursor for ozone production in the model, while the fractionation in different species and total amount of non-methane volatile organic compounds (NMVOC) emissions are less important. Naturally emitted NMVOC, isoprene, is an important precursor of surface ozone at certain conditions, and a better inventory of these emissions is needed. Deposition velocities of ozone also have impact on surface concentrations. To improve the model performance, it is important to add a land use inventory with corresponding deposition velocities.

Trace elements in near-ground atmospheric aerosols were investigated in Dar es Salaam, Tanzania. Particles were collected at two sites, one urban and one rural, during, two months with different meteorological conditions. The samplers, dichotomous impactors, segregate the particles into two size fractions, fine (PM2.5, d(a) < 2.5 mum) and coarse (2.5 < d(a) < 10 mum). A sharp cyclone was used to sample finer particles (PM1, d(a) < 1 mum). Meteorological parameters were also examined at both sites. An EDXRF spectrometer, based on three-axial geometry, was used for quantitative elemental analysis. Concentrations of elements heavier than phosphorus were determined. Also, the content of black carbon on the filters was measured with a reflectometer. The elemental concentrations were compared with respect to season and geographical location in the city. The levels of different species in Dar es Salaam were also compared with similar data from other African and European countries. This showed low values of Pb with respect to the size of the city and no legislation on the use of leaded petrol, that often is the main source of lead. High values of Cl were also found, as would be expected in a coastal city. The coarse particles in the air, originating from soil, had a different composition in Dar es Salaam than in Gaborone, Botswana, and the concentration of black carbon was higher than in other cities. On the basis of the data collected, source assignments were made and the following sources found; sea-spray, soil, city road dust, biomass burning industries and traffic. Comparing the concentrations of different elements in PM2.5 and PM1 revealed that black carbon, Zn, Pb, K and Br are present only in the smallest particles. Copyright (C) 2005 John Wiley Sons, Ltd.

Model calculations have been performed to estimate the effects of emissions in Stockholm on the population exposure to particulate matter (PM) outside the city.The impacts of five different emissions were investigated: Road traffic exhaust, split into Light Duty Vehicles (LDV) and Heavy Duty Vehicles(HDV), Sea Traffic, Power Plants and Residential Heating. The emissions from non-exhaust (mainly road wear due to use of studded tyres) were also treated, in addition to combustion sources.The uncertainties in the emission estimates for Residential Heating using biomass (wood) are very large but it seems that it is an important PM source in Stockholm. In this report two estimates of the emissions have been used. In the lowest estimate, which seems more realistic, the contribution to population exposure of directly emitted combustion particles from residential heating is of similar magnitude (37%) as the contribution from road traffic exaust (42%). For all sources, except Sea Traffic, the total population exposure to combustion PM is much larger within Stockholm than outside; for shipping the total exposure is about as large outside the city as within.For all sources, except residential heating, the secondary inorganic aerosol (SIA) exposure is higher than the combustion particle exposure. Non-exhaust particles dominate the total impact on PM10 exposure, contributing about 60-70% to the total exposure, due to all the studied sources in Stockholm. The calculated population exposure due to the wear particles is to a very large extent (87%) occurring within the Greater Stockholm area.

We have investigated the potential impact on organic aerosol formation from biotic stress-induced emissions (SIE) of organic molecules from forests in Europe (north of lat. 45 degrees N). Emission estimates for sesquiterpenes (SQT), methyl salicylate (MeSA) and unsaturated C-17 compounds, due to different stressors, are based on experiments in the Julich Plant Atmosphere Chamber (JPAC), combined with estimates of the fraction of stressed trees in Europe based on reported observed tree damage. SIE were introduced in the EMEP MSC-W chemical transport model and secondary organic aerosol (SOA) yields from the SIE were taken from the JPAC experiments. Based on estimates of current levels of infestation and the JPAC aerosol yields, the model results suggest that the contribution to SOA in large parts of Europe may be substantial. It is possible that SIE contributes as much, or more, to organic aerosol than the constitutive biogenic VOC emissions, at least during some periods. Based on the assumptions in this study, SIE-SOA are estimated to constitute between 50 and 70% of the total biogenic SOA (BSOA) in a current-situation scenario where the biotic stress in northern and central European forests causes large SIE of MeSA and SQT. An alternative current-situation scenario with lower SIE, consisting solely of SQT, leads to lower SIE-SOA, between 20 and 40% of the total BSOA. Hypothetical future scenarios with increased SIE, due to higher degrees of biotic stress, show that SOA formation due to SIE can become even larger. Unsaturated C17 BVOC (biogenic volatile organic compounds) emitted by spruce infested by the forest-honey generating bark louse, Cinara pilicornis, have a high SOA-forming potential. A model scenario investigating the effect of a regional, episodic infestation of Cinara pilicornis in Baden-Wurttemberg, corresponding to a year with high production of forest honey, shows that these types of events could lead to very large organic aerosol formation in the infested region. We have used the best available laboratory data on biotic SIE applicable to northern and central European forests. Using these data and associated assumptions, we have shown that SIE are potentially important for SOA formation but the magnitude of the impact is uncertain and needs to be constrained by further laboratory, field and modelling studies. As an example, the MeSA, which is released as a consequence of various types of biotic stress, is found to have a potentially large impact on SIE-SOA in Europe, but different assumptions regarding the nighttime chemistry of MeSA can change its SOA potential substantially. Thus, further investigations of the atmospheric chemistry of MeSA and observational field studies are needed to clarify the role of this compound in the atmosphere.

A new organic aerosol module has been implemented into the EMEP chemical transport model. Four different volatility basis set (VBS) schemes have been tested in long-term simulations for Europe, covering the six years 2002-2007. Different assumptions regarding partitioning of primary organic aerosol and aging of primary semi-volatile and intermediate volatility organic carbon (S/IVOC) species and secondary organic aerosol (SOA) have been explored. Model results are compared to filter measurements, aerosol mass spectrometry (AMS) data and source apportionment studies, as well as to other model studies. The present study indicates that many different sources contribute significantly to organic aerosol in Europe. Biogenic and anthropogenic SOA, residential wood combustion and vegetation fire emissions may all contribute more than 10% each over substantial parts of Europe. This study shows smaller contributions from biogenic SOA to organic aerosol in Europe than earlier work, but relatively greater anthropogenic SOA. Simple VBS based organic aerosol models can give reasonably good results for summer conditions but more observational studies are needed to constrain the VBS parameterisations and to help improve emission inventories. The volatility distribution of primary emissions is one important issue for further work. Emissions of volatile organic compounds from biogenic sources are also highly uncertain and need further validation. We can not reproduce winter levels of organic aerosol in Europe, and there are many indications that the present emission inventories substantially underestimate emissions from residential wood combustion in large parts of Europe.

The atmospheric dispersion of NOx and PM10 was simulated with a second generation Gaussian model over a medium-size south-European city. Microscopic traffic models calibrated with GPS data were used to derive typical driving cycles for each road link, while instantaneous emissions were estimated applying a combined Vehicle Specific Power/Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (VSP/EMEP) methodology. Site-specific background concentrations were estimated using time series analysis and a low-pass filter applied to local observations. Air quality modelling results are compared against measurements at two locations for a 1 week period. 78% of the results are within a factor of two of the observations for 1-h average concentrations, increasing to 94% for daily averages. Correlation significantly improves when background is added, with an average of 0.89 for the 24 h record. The results highlight the potential of detailed traffic and instantaneous exhaust emissions estimates, together with filtered urban background, to provide accurate input data to Gaussian models applied at the urban scale. (C) 2016 Elsevier Ltd. All rights reserved.

The project was initiated by the Swedish Environmental Protection Agency in order to improve the basis for making standards for PM-10 concentrations in urban air. Model development has been made for Norrköping and Gothenburg. Modelling has been necessary of both long-range and local contributions.

The long-range dispersion has been simulated by the MATCH-Europe and MATCH-Sweden models, the former being a conventional dispersion model based on meteorology and emission data and the latter including also results from background air pollution measurements in Sweden and neighbouring countries.

For the local scale, both car exhaust panicles and resuspended particles from a traffic source inventory are dispersed in the city using meteorological data and a Gaussian dispersion mode! and, if needed, a street canyon dispersion submodel. For panicle resuspension, a new model has been developed. The parameters of the resuspension model have been adjusted to two streets/measuring periods in Norrköping.

At street level in Norrköping, the local model showed to contribute to a large part of the total concentration, especially in late winter and early spring due to resuspension. The MATCH mode! gives same underestimate due to the absence of organic compounds and simulation of PM-2.5 instead of PM-10. However, at some episodes in Norrköping and, in general, for a station at roof level in central Gothenburg and at the rural station Aspvreten, the model estimates of regional PM-2.5 concentrations constitute a larger part of the observed PM-10 concentrations. A good covariation in time with measured data occurs for both the MATCH model and the local model.

Linear particle depolarization ratio is presented for three case studies from the NASA Langley airborne High Spectral Resolution Lidar-2 (HSRL-2). Particle depolarization ratio from lidar is an indicator of non-spherical particles and is sensitive to the fraction of non-spherical particles and their size. The HSRL-2 instrument measures depolarization at three wavelengths: 355, 532, and 1064 nm. The three measurement cases presented here include two cases of dust-dominated aerosol and one case of smoke aerosol. These cases have partial analogs in earlier HSRL-1 depolarization measurements at 532 and 1064 nm and in literature, but the availability of three wavelengths gives additional insight into different scenarios for non-spherical particles in the atmosphere. A case of transported Saharan dust has a spectral dependence with a peak of 0.30 at 532 nm with smaller particle depolarization ratios of 0.27 and 0.25 at 1064 and 355 nm, respectively. A case of aerosol containing locally generated wind-blown North American dust has a maximum of 0.38 at 1064 nm, decreasing to 0.37 and 0.24 at 532 and 355 nm, respectively. The cause of the maximum at 1064 nm is inferred to be very large particles that have not settled out of the dust layer. The smoke layer has the opposite spectral dependence, with the peak of 0.24 at 355 nm, decreasing to 0.09 and 0.02 at 532 and 1064 nm, respectively. The depolarization in the smoke case may be explained by the presence of coated soot aggregates. We note that in these specific case studies, the linear particle depolarization ratio for smoke and dust-dominated aerosol are more similar at 355 nm than at 532 nm, having possible implications for using the particle depolarization ratio at a single wavelength for aerosol typing.

: This study investigates the impacts of climate change scenario on summer heat waves’ (HWs) and winter cold spells’ (CSs) characteristics for 12 locations over the Iberian Peninsula (IP). These characteristics are duration, recovery factor and intensity. Two future time slices of the chosen scenario are studied, namely, the periods 2046–2065 and 2081–2100 which are compared with a reference climate for the recent-past (1986–2005). The RCP8.5 greenhouse gas emission scenario is considered. The minimum and maximum daily temperature were obtained for these periods through regional model simulations using the Weather and Research Forecast (WRF) model forced with the MPI-ESM-LR model. The model was validated against EOBS and SPAIN02 datasets. The model shows 90th/10th percentile temperature (i.e. thresholds to identify HW/CS) biases. Therefore, HW/CS numbers and properties were evaluated using the model’s respective thresholds. HW/CS numbers and characteristics were also compared between the model and EOBS derived data. Probability density functions (PDFs) of the duration, recovery factor and intensity show significant changes in the mean and variance for the summer HWs. Differences, between future and recent-past climate in the extremes are evaluated by the 95th percentile which show an increase in the duration and intensity of the HWs for the future time slices. Very few CSs were detectable in the mid-term future (2046–2065) and none in the long-term future (2080–2100), except for Barcelona. For most locations, the CS for the future are of smaller duration and intensity. The PDF of the recovery factor suggests smaller absolute differences between the minimum and maximum temperature during winter which is also confirmed by the percentile analysis. The increase in the duration and intensity of HWs is greater in the long-term future than in the mid-term future, pointing for a warmer IP with more and longer HWs towards the end of the XXI century

An intercomparison study involving eight long-range transport models for sulfur deposition in East Asia has been initiated, The participating models included Eulerian and Lagrangian frameworks, with a wide variety of vertical resolutions and numerical approaches. Results from this study, in which models used common data sets for emissions, meteorology, and dry, wet and chemical conversion rates, are reported and discussed. Model results for sulfur dioxide and sulfate concentrations, wet deposition amounts, for the period January and May 1993, are compared with observed quantities at 18 surface sites in East Asia. At many sites the ensemble of models is found to have high skill in predicting observed quantities. At other sites all models show poor predictive capabilities. Source-receptor relationships estimated by the models are also compared. The models show a high degree of consistency in identifying the main source-receptor relationships, as well as in the relative contributions of wet/dry pathways for removal. But at some locations estimated deposition amounts can vary by a factor or 5. The influence of model structure and parameters on model performance is discussed. The main factors determining the deposition fields are the emissions and underlying meteorological fields. Model structure in terms of vertical resolution is found to be more important than the parameterizations used for chemical conversion and removal, as these processes are highly coupled and often work in compensating directions. (C) 2002 Elsevier Science Ltd. All rights reserved.

To help improve the use of models in science & policy analysis in Asia it is necessary to have a better understanding of model performance and uncertainties. Towards this goal an intercomparison exercise has been initiated as a collaborative study of scientists interested in long-range transport in East Asia. An overview of this study is presented in this paper. The study consists of a set of prescribed test calculations with carefully controlled experiments. Models used the same domain, emission inventory, model parameters, meteorological conditions, etc. Two periods (January and May 1993) were selected to reflect long-range transport conditions under two distinct seasons. During these periods measurements of sulfur concentrations and deposition were made throughout the study region using identical sampling and analysis protocols. The intercomparison activity consists of four tasks (Blind Test, Fixed Parameter Test, Source Receptor test, and Tuning Test). All participants were asked to do Task A, and as many of the other tasks as possible. To date seven different models have participated in this study. Results and key findings are presented.

Results from the Model Intercomparison Study Asia Phase II (MICS-Asia II) are presented. Nine different regional modeling groups simulated chemistry and transport of ozone (O-3), secondary aerosol, acid deposition, and associated precursors, using common emissions and boundary conditions derived from a global model. Four-month-long periods, representing 2 years and three seasons (i.e., March, July, and December in 2001, and March in 2002), are analyzed. New observational data, obtained under the EANET (the Acid Deposition Monitoring Network in East Asia) monitoring program, were made available for this study, and these data provide a regional database to compare with model simulations. The analysis focused around seven subject areas: O-3 and related precursors, aerosols, acid deposition, global inflow of pollutants and precursor to Asia, model sensitivities to aerosol parameterization, analysis of emission fields, and detailed analyses of individual models, each of which is presented in a companion paper in this issue of Atmospheric Environment. This overview discusses the major findings of the study, as well as information on common emissions, meteorological conditions, and observations. (C) 2007 Elsevier Ltd. All rights reserved.

Ozone air pollution is identified as one of the main threats bearing upon human health and ecosystems, with 25 000 deaths in 2005 attributed to surface ozone in Europe (IIASA 2013 TSAP Report #10). In addition, there is a concern that climate change could negate ozone pollution mitigation strategies, making them insufficient over the long run and jeopardising chances to meet the long term objective set by the European Union Directive of 2008 (Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008) (60 ppbv, daily maximum). This effect has been termed the ozone climate penalty. One way of assessing this climate penalty is by driving chemistry-transport models with future climate projections while holding the ozone precursor emissions constant (although the climate penalty may also be influenced by changes in emission of precursors). Here we present an analysis of the robustness of the climate penalty in Europe across time periods and scenarios by analysing the databases underlying 11 articles published on the topic since 2007, i.e. a total of 25 model projections. This substantial body of literature has never been explored to assess the uncertainty and robustness of the climate ozone penalty because of the use of different scenarios, time periods and ozone metrics. Despite the variability of model design and setup in this database of 25 model projection, the present meta-analysis demonstrates the significance and robustness of the impact of climate change on European surface ozone with a latitudinal gradient from a penalty bearing upon large parts of continental Europe and a benefit over the North Atlantic region of the domain. Future climate scenarios present a penalty for summertime (JJA) surface ozone by the end of the century (2071-2100) of at most 5 ppbv. Over European land surfaces, the 95% confidence interval of JJA ozone change is [0.44; 0.64] and [0.99; 1.50] ppbv for the 2041-2070 and 2071-2100 time windows, respectively.

This paper presents the aerosol budget over Europe in 2006 calculated with the global transport model TM5 coupled to the size-resolved aerosol module M7. Comparison with ground observations indicates that the model reproduces the observed concentrations quite well with an expected slight underestimation of PM10 due to missing emissions (e.g. resuspension). We model that a little less than half of the anthropogenic aerosols emitted in Europe are exported and the rest is removed by deposition. The anthropogenic aerosols are removed mostly by rain (95%) and only 5% is removed by dry deposition. For the larger natural aerosols, especially sea salt, a larger fraction is removed by dry processes (sea salt: 70%, mineral dust: 35%). We model transport of aerosols in the jet stream in the higher atmosphere and an import of Sahara dust from the south at high altitudes. Comparison with optical measurements shows that the model reproduces the Angstrom parameter very well, which indicates a correct simulation of the aerosol size distribution. However, we underestimate the aerosol optical depth. Because the surface concentrations are close to the observations, the shortage of aerosol in the model is probably at higher altitudes. We show that the discrepancies are mainly caused by an overestimation of wet-removal rates. To match the observations, the wet-removal rates have to be scaled down by a factor of about 5. In that case the modelled ground-level concentrations of sulphate and sea salt increase by 50% (which deteriorates the match), while other components stay roughly the same. Finally, it is shown that in particular events, improved fire emission estimates may significantly improve the ability of the model to simulate the aerosol optical depth. We stress that discrepancies in aerosol models can be adequately analysed if all models would provide (regional) aerosol budgets, as presented in the current study.

Non-exhaust traffic induced emissions are a major source of airborne particulate matter in most European countries. This is particularly important in Nordic and Alpine countries where winter time road traction maintenance occurs, e.g. salting and sanding, and where studded tyres are used. Though the total mass generated by wear sources is a key factor in non-exhaust emissions, these emissions are also strongly controlled by surface moisture conditions. In this paper, Part 2, the road surface moisture submodel of a coupled road dust and surface moisture model (NORTRIP) is described. We present a description of the road surface moisture part of the model and apply the coupled model to seven sites in Stockholm, Oslo, Helsinki and Copenhagen over 18 separate periods, ranging from 3.5 to 24 months. At two sites surface moisture measurements are available and the moisture sub-model is compared directly to these observations. The model predicts the frequency of wet roads well at both sites, with an average fractional bias of -2.6%. The model is found to correctly predict the hourly surface state, wet or dry, 85% of the time. From the 18 periods modelled using the coupled model an average absolute fractional bias of 15% for PM10 concentrations was found. Similarly the model predicts the 90'th daily mean percentiles of PMio with an average absolute bias of 19% and an average correlation (R-2) of 0.49. When surface moisture is not included in the modelling then this average correlation is reduced to 0.16, demonstrating the importance of the surface moisture conditions. Tests have been carried out to assess the sensitivity of the model to model parameters and input data. The model provides a useful tool for air quality management and for improving our understanding of non-exhaust traffic emissions. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

Non-exhaust traffic induced emissions are a major source of particle mass in most European countries. This is particularly important in Nordic and Alpine countries where winter time road traction maintenance occurs, e.g. salting and sanding, and where studded tyres are used. In this paper, Part 1, the road dust sub-model of a coupled road dust and surface moisture model (NORTRIP) is described. The model provides a generalised process based formulation of the non-exhaust emissions, with emphasis on the contribution of road wear, suspension, surface dust loading and the effect of road surface moisture (retention of wear particles and suspended emissions). The model is intended for use as a tool for air quality managers to help study the impact of mitigation measures and policies. We present a description of the road dust sub-model and apply the model to two sites in Stockholm and Copenhagen where seven years of data with surface moisture measurements are available. For the site in Stockholm, where studded tyres are in use, the model predicts the PM10 concentrations very well with correlations (R-2) in the range of R-2 = 0.76-0.91 for daily mean PM10. The model also reproduces well the impact of a reduction in studded tyres at this site. For the site in Copenhagen the correlation is lower, in the range 0.44-0.51. The addition of salt is described in the model and at both sites this leads to improved correlations due to additional salt emissions. For future use of the model a number of model parameters, e.g. wear factors and suspension rates, still need to be refined. The effect of sanding on PM10 emissions is also presented but more information will be required before this can be confidently applied for management applications. (C) 2013 Elsevier Ltd. All rights reserved.

Simulating the radiative impacts of aerosols located above liquid water clouds presents a significant challenge. In particular, absorbing aerosols, such as smoke, may have significant impact in such situations and even change the sign of net radiative forcing. It is not possible to reliably obtain information on such overlap events from existing passive satellite sensors. However, the CALIOP instrument onboard NASA's CALIPSO satellite allows us to examine these events with unprecedented accuracy. Using four years of collocated CALIPSO 5 km Aerosol and Cloud Layer Version 3 Products (June 2006 May 2010), we quantify, for the first time, the characteristics of overlapping aerosol and water cloud layers globally. We investigate seasonal variability in these characteristics over six latitude bands to understand the hemispheric differences when all aerosol types are included in the analysis (the AAO case). We also investigate frequency of smoke aerosol-cloud overlap (the SAO case). Globally, the frequency is highest during the JJA months in the AAO case, while for the SAO case, it is highest in the SON months. The seasonal mean overlap frequency can regionally exceed 20% in the AAO case and 10% in the SAO case. In about 5-10% cases the vertical distance between aerosol and cloud layers is less than 100 m, while about in 45-60% cases it less than a kilometer in the annual means for different latitudinal bands. In about 70-80% cases, aerosol layers are less than a kilometer thick, while in about 18-22% cases they are 1-2 km thick. The frequency of aerosol layers 2-3 km thick is about 4-5% in the tropical belts during overlap events. Over the regions where high aerosol loadings are present, the overlap frequency can be up to 50% higher when quality criteria on aerosol/cloud feature detection are relaxed. Over the polar regions, more than 50% of the overlapping aerosol layers have optical thickness less than 0.02, but the contribution from the relatively optically thicker aerosol layers increases towards the equatorial regions in both hemispheres. The results suggest that the frequency of occurrence of overlap events is far from being negligible globally.

Temperature inversions influence the local air quality at smaller scales and the pollution transport at larger spatio-temporal scales and are one of the most commonly observed meteorological phenomena over Scandinavia (54 degrees N-70 degrees N, 0-30 degrees E) during winter. Here, apart from presenting key statistics on temperature inversions, a large-scale co-variation of inversion strength and carbon monoxide (CO), an ideal pollution tracer, is further quantified at six vertical levels in the free troposphere during three distinct meteorological regimes that are identified based on inversion strength. Collocated temperature and CO profiles from Atmospheric Infrared Sounder (AIRS) are used for this purpose. Higher values of CO (up to 15%) are observed over Scandinavia during weakly stable regimes at all vertical levels studied, whereas lower CO values (up to 10%) are observed when inversions become stronger and elevated. The observed systematic co-variation between CO and inversion strength in three meteorological regimes is most likely explained by the efficacy of long-range transport to influence tropospheric composition over Scandinavia. We argue that this large-scale co-variation of temperature inversions and CO would be a robust metric to test coupling of large-scale meteorology and chemistry in transport models. (C) 2012 Elsevier Ltd. All rights reserved.

The main purpose of this study is to underline the sensitivity of cloud liquid water content (LWC) estimates purely to 1) the shape of computationally simplified temperature-dependent thermodynamic phase and 2) the range of subzero temperatures covered to partition total cloud condensate into liquid and ice fractions. Linear, quadratic, or sigmoid-shaped functions for subfreezing temperatures (down to -20 degrees or -40 degrees C) are often used in climate models and reanalysis datasets for partitioning total condensate. The global vertical profiles of clouds obtained from CloudSat for the 4-yr period June 2006-May 2010 are used for sensitivity analysis and the quantitative estimates of sensitivities based on these realistic cloud profiles are provided. It is found that three cloud regimes in particular-convective clouds in the tropics, low-level clouds in the northern high latitudes, and middle-level clouds over the midlatitudes and Southern Ocean-are most sensitive to assumptions on thermodynamic phase. In these clouds, the LWC estimates based purely on quadratic or sigmoid-shaped functions with a temperature range down to -20 degrees C can differ by up to 20%-40% over the tropics (in seasonal means). 10%-30% over the midlatitudes, and up to 50% over high latitudes compared to a linear assumption. When the temperature range is extended down to -40 degrees C. LWC estimates in the sigmoid case can be much higher than the above values over high-latitude regions compared to the commonly used case with quadratic dependency down to -20 C. This sensitivity study emphasizes the need to critically investigate radiative impacts of cloud thermodynamic phase assumptions in simplified climate models and reanalysis datasets.

The main purpose of this study is to investigate the influence of the Arctic Oscillation (AO), the dominant mode of natural variability over the northerly high latitudes, on the spatial (horizontal and vertical) distribution of clouds in the Arctic. To that end, we use a suite of sensors on-board NASA's A-Train satellites that provide accurate observations of the distribution of clouds along with information on atmospheric thermodynamics. Data from three independent sensors are used (AQUA-AIRS, CALIOP-CALIPSO and CPR-CloudSat) covering two time periods (winter half years, November through March, of 2002-2011 and 2006-2011, respectively) along with data from the ERA-Interim reanalysis. We show that the zonal vertical distribution of cloud fraction anomalies averaged over 67-82 degrees N to a first approximation follows a dipole structure (referred to as "Greenland cloud dipole anomaly", GCDA), such that during the positive phase of the AO, positive and negative cloud anomalies are observed eastwards and westward of Greenland respectively, while the opposite is true for the negative phase of AO. By investigating the concurrent meteorological conditions (temperature, humidity and winds), we show that differences in the meridional energy and moisture transport during the positive and negative phases of the AO and the associated thermodynamics are responsible for the conditions that are conducive for the formation of this dipole structure. All three satellite sensors broadly observe this large-scale GCDA despite differences in their sensitivities, spatio-temporal and vertical resolutions, and the available lengths of data records, indicating the robustness of the results. The present study also provides a compelling case to carry out process-based evaluation of global and regional climate models.

Clouds play a crucial role in the Arctic climate system. Therefore, it is essential to accurately and reliably quantify and understand cloud properties over the Arctic. It is also important to monitor and attribute changes in Arctic clouds. Here, we exploit the capability of the CALIPSO-CALIOP instrument and provide comprehensive statistics of tropospheric thin clouds, otherwise extremely difficult to monitor from passive satellite sensors. We use 4 yr of data (June 2006-May 2010) over the circumpolar Arctic, here defined as 67-82 degrees N, and characterize probability density functions of cloud base and top heights, geometrical thickness and zonal distribution of such cloud layers, separately for water and ice phases, and discuss seasonal variability of these properties. When computed for the entire study area, probability density functions of cloud base and top heights and geometrical thickness peak at 200-400, 1000-2000 and 400-800 m, respectively, for thin water clouds, while for ice clouds they peak at 6-8, 7-9 and 400-1000 m, respectively. In general, liquid clouds were often identified below 2 km during all seasons, whereas ice clouds were sensed throughout the majority of the upper troposphere and also, but to a smaller extent, below 2 km for all seasons.