Ambient air quality and deposition trends at rural stations in the Czech Republic during 1993-2001

The paper presents the trends in ambient SO2, NOx and O-3 concentrations, 4- and NO3 concentrations in precipitation and S/SO42- and N/NO3- wet-only atmospheric deposition over the period 1993-2001. The trends are presented for selected rural sites operated by the Czech Hydrometeorological Institute. The results show that the remarkable decrease of SO2 emissions during the 1990s was followed by a statistically significant downward trend in SO2 ambient levels, SO42- concentration in precipitation and S/SO42- wet-only deposition. SO42- wet-only deposition decreased by ca. 30% while ambient SO2 concentrations decreased by ca. 80%, in line with total Czech SO2 emissions over the period 1993-2001. In contrast, the ambient NOx concentrations show a significantly downward trend at only five out of 14 stations, while other stations do not have any trend. N/NO3- wet deposition does not show any trend between 1993 and 2001. This corresponds to a less pronounced decrease in NO, emissions. N/NO3- wet deposition decreased at some stations by ca. 10% (the trend is not statistically significant), while at some stations it had not decreased at all. Ambient NOx concentrations decreased by approximately 35%, NO, emissions decreased by ca. 30%. The SO2 limit value of 20 mug m(-3) for vegetation protection, though vastly exceeded in the past, has not been exceeded since 1999, while the NO, limit value of 30 mug m(-3) for vegetation protection has never been exceeded at the 14 stations analysed. Elevated O-3 concentrations and, consequently, AOT40 limit exceedances were recorded at most of the stations under review. (C) 2003 Elsevier Ltd. All rights reserved.