Analysis of exceedances in the daily PM 10 mass concentration (50 μg m −3) at a roadside station in Leipzig, Germany
Five years of PM 10 and PM 2.5 ambient air measurements at a roadside, an urban, and a regional background site in Leipzig (Germany) were analyzed for violations of the legal PM 10 limit value (EC, 1999). The annual mean PM 10 concentrations at the three sites were well below the legal threshold of 40 μg m −3 (32.6, 22.0 and 21.7 μg m −3, respectively). At roadside, the daily maximum value of 50 μg m −3 was exceeded on 232 days (13% of all days) in 2005–2009, which led to a violation of the EC directive in three out of five years. We analysed the meteorological factors and local source contributions that eventually led to the exceedances of the daily limit value. As noted in other urban environments before, most exceedance days were observed in the cold season. Exceedance days were most probable under synoptic situations characterised by stagnant winds, low temperatures and strong temperature inversions in winter time. However, these extreme situations accounted for only less than half of the exeedance days. We also noticed a significant number of exceedance days that occurred in the cold season under south-westerly winds, and in the warm season in the presence of easterly winds. Our analysis suggests that local as well as regional sources of PM are equally responsible for exceedances days at the roadside site. The conclusion is that a combined effort of local, national and international reduction measures appears most likely to avoid systematic exceedances of the daily limit value in the future.