I föreliggande rapport redovisas resultat från 1997, 1998 och 1999 års mätningar av luftens och nederbördens sammansättning i bakgrundsmiljö i Sverige. Rapporten redovisar mätresultat från de båda nationella övervakningsnäten EMEP och Luft- och nederbördskemiska nätet. I rapporten redovisas även de spridningsoch depositionsberäkningar som gjorts med Sverigemodellen för 1997 och 1998. Samtliga mätningar drivs av IVL medan modellberäkningarna med Sverigemodellen utförs av SMHI. Verksamheten finansieras av Miljöövervakningsenheten vid Naturvårdsverket.

Measurements of the composition of air and precipitation in background areas in Sweden during 1997, 1998 and 1999 are presented in the report. Results from two national networks, EMEP and the Swedish Precipitation Chemistry Network, both run by IVL Swedish Environmental Research Institute, are compiled and evaluated. Included in the presentation are also model calculations of dispersion and deposition of sulphur- and nitrogen compounds over Sweden. The modelling is based on monitoring results from 1997 and the calculations have been made using the MATCH-Sweden modelling system developed by SMHI, Swedish Meteorological and Hydrological Institute. The Swedish Environmental Protection Agency finances the activities. The monitoring programmes during the three years have included daily sampling of sulphur dioxide, nitrogen dioxide and particle bound sulphate in air at six stations 1997 and five stations 1998 and 1999. Daily measurements of soot, total-nitrate and total-ammonium have been performed at four stations. Monthly sampling of sulphur dioxide and nitrogen dioxide has been made at 12 stations 1997 and 1998 and at 13 stations 1999. Ozone concentrations in ground-level air have been monitored at six stations. Measurements of mercury in air have been performed at two stations regarding total gaseous mercury (TGM) and particle bound mercury. The measurements of sulphur and nitrogen compounds in air displayed a decreasing gradient from south to north. Generally, the higher concentrations of sulphur dioxide, sulphate, soot and nitrogen dioxide are found during winter, while high levels of ozone are registered during spring or early summer. The remaining compounds show a more uniform concentration during the seasons. The annual averages were comparable to, or lower, than previous years. The highest annual average air concentration of ground-level ozone was, as previous years, registered in Esrange. Ozone levels above 180 μg/m3 were not registered during the period. AOT40 values were on a comparable level with previous years, except for southern Sweden 1998 where AOT40 values were unusually low. Daily sampling of precipitation using a wet-only sampler has been made at one station and weekly sampling at three stations. At nearly 30 stations, monthly sampling using bulk-samplers was carried out. The precipitation samples were analysed with respect to pH, sulphate, nitrate, ammonium, chloride, calcium, magnesium, sodium and potassium. At four stations sampling of precipitation for analysis of heavy metals, total-mercury and methyl-mercury was made. The components in precipitation generally showed a decreasing gradient from south to north. The concentration of sulphate has decreased somewhat compared to previous years. The annual averages of pH showed higher values in northern Sweden than in the south. The pH values were slightly higher throughout the country than in earlier years. The concentrations in precipitation and the deposition of heavy metals and mercury generally showed lower values in northern and higher values in southern Sweden. The MATCH-Sweden model is a three-dimensional Eulerian atmospheric dispersion model, which is used for calculation of dispersion and deposition of air pollutants over Sweden. This model system also includes a method for data assimilation of measured concentrations in air and precipitation. In this report only some few examples of calculated annual mean concentrations and annual deposition maps for 1997 and 1998 are presented for sulphur, oxidised and reduced nitrogen. The MATCH-Sweden model has also been used to estimate air pollution budgets for Sweden for the years 1997 and 1998. The Swedish net import of air pollutants is substantial for sulphur and NHx-nitrogen. The Swedish contribution to deposition over Sweden is about 7 % for sulphur, 11 % for NOx-nitrogen and 20 % for NHxnitrogen. MATCH-Sweden results show somewhat larger deposition values than the EMEP model over Sweden for sulphur and NOx-nitrogen. For NHx-nitrogen the values are much larger, especially in Northern Sweden where the MATCH-Sweden values are 2-3 times larger than the EMEP model.