Anthropogenic emissions are a dominant contributor to air pollution.
Consequently, mitigation policies have attempted to reduce anthropogenic
pollution emissions in Europe since the 1990s. To evaluate the
effectiveness of these mitigation policies, the German Ultrafine Aerosol
Network (GUAN) was established in 2008, focusing on black carbon and
sub-micrometer aerosol particles, especially ultrafine particles. In
this investigation, trends of the size-resolved particle number
concentrations (PNC) and the equivalent black carbon (eBC) mass
concentration over a 10-year period (2009–2018) were evaluated for 16
observational sites for different environments among GUAN. The trend
analysis was done for both, the full-length time series and on subsets
of the time series in order to test the reliability of the results. The
results show generally decreasing trends of both, the PNCs for all size
ranges as well as eBC mass concentrations in all environments, except
PNC in 10–30 nm at regional background and mountain sites. The annual
slope of the eBC mass concentration varies between −7.7 % and −1.8 % per
year. The slopes of the PNCs varies from −6.3 % to 2.7 %, −7.0 % to
−2.0 %, and −9.5 % to −1.5 % per year (only significant trends) for
10–30 nm, 30–200 nm, and 200–800 nm particle diameter, respectively. The
regional Mann-Kendall test yielded regional-scale trends of eBC mass
concentration, N[30–200] and N[200–800]
of −3.8 %, −2.0 % and −2.4 %, respectively, indicating an overall
decreasing trend for eBC mass concentration and sub-micrometer PNC
(except N[10–30]) all over Germany. The most
significant decrease was observed on working days and during daytime in
urban areas, which implies a strong evidence of reduced anthropogenic
emissions. For the seasonal trends, stronger reductions were observed in
winter. Possible reasons for this reduction can be the increased
average ambient temperatures and wind speed in winter, which resulted in
less domestic heating and stronger dilution. In addition, decreased
precipitation in summer also diminishes the decrease of the PNCs and eBC
mass concentration. For the period of interest, there were no
significant changes in long-range transport patterns. The most likely
factors for the observed decreasing trends are declining anthropogenic
emissions due to emission mitigation policies of the European Union.