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 O3 concentrations, SO42− 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. S/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 NOx 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%, NOx emissions decreased by ca. 30%. The SO2 limit value of 20 μg m−3 for vegetation protection, though vastly exceeded in the past, has not been exceeded since 1999, while the NOx limit value of 30 μg m−3 for vegetation protection has never been exceeded at the 14 stations analysed. Elevated O3 concentrations and, consequently, AOT40 limit exceedances were recorded at most of the stations under review.