Aerosol immission maps and trends over Germany with hourly data at four rural background stations from 2009 to 2018

Abstract

Abstract. Ten years of hourly aerosol and gas data at four rural German stations have been combined with hourly back trajectories to the stations and inventories of the European EDGAR emission database yielding immission maps over Germany of PM10, particle number concentrations, and equivalent black carbon (eBC). The maps reflect aerosol emissions modified with atmospheric processes during transport between sources and receptor sites. Compared to emission maps strong Western European emission centers do not necessarily dominate the downwind concentrations because their emissions are reduced by atmospheric processes on the way to the receptor area. PM10, eBC, and to some extent also particle number concentrations are rather controlled by emissions from Southeastern Europe from which pollution transport often occurs under dryer conditions. Newly formed particles are found in air masses from a broad sector reaching from Southern Germany to Western Europe which we explain with gaseous particle precursors coming with little wet scavenging from this region. Annual emissions for 2009 of PM10, BC, SO2, and NOx were accumulated along each trajectory and compared with the corresponding measured time series. The agreement of each pair of time series was optimized by varying monthly factors and annual factors on the 2009 emissions. This approach yielded broader summer emission minima than published values that were partly displaced from the midsummer positions. For BC, SO2, and NOx stronger emission-reductions were determined than what GEA and EEA reported. These findings are emphasized with 2017 as endpoint of the trend from which on our study shows emission increases. Comparing calculated trends with emission trends in neighboring countries as published by EEA supports the explanation that the observed trends are to some extent due to changes in imported air masses. Most strongly this holds for SO2, the trend of which follows that of Romanian emissions rather well.