Aerosol microphysical properties during anticyclonic flow conditions over Europe

Aerosols play an important role in atmospheric physics. The airborne particles in diameters of a few nanometres to some micrometres affect the climate system by altering the energy balance of the atmosphere. However, the quantification of the climate effect is an open question until today. Large uncertainties exist in the knowledge of the global aerosol distribution and their properties. The present work assesses the spatial and temporal distribution and variability of aerosol particles and their properties above Europe during stable synoptic conditions. A data set of airborne measurements unique in its spatial dimensions over Europe was obtained within this work in May 2008. It covers microphysical aerosol properties throughout the whole tropospheric column above Central and Western Europe. The airborne aerosol measurements were performed aboard the DLR Falcon 20 within the EUCAARI-LONGREX field campaign. The aircraft operated from Oberpfaffenhofen, Germany. The influence of source contributions on the aerosol particles and ageing processes over a densely populated region were measured and analysed using a new developed trajectory analysis tool (FLYTUL). The trajectory analysis tool uses the EDGAR 3.2 Fast Track 2000 dataset to quantify the source contributions along each trajectory of a trajectory bundle for a qualitative classification of the air mass. Meteorological information along the air mass transport pathway is retrieved from the ECMWF. The prevailing anticyclonic conditions led to an increase of particulate matter in the continental boundary layer. Total aerosol number concentrations reached 22000 cm−3, number concentrations of accumulation mode particles 1600 cm−3. The volume fraction of secondary aerosol matter increased to 95% for submicron particles due to coagulation processes and condensation of the abundant aerosol precursor gases within the dry and stable meteorological conditions. A positive gradient of particulate matter was observed along the anticyclonic transport pathway from the Baltic Sea towards the Benelux States and Southern England. The vertical aerosol distribution featured clean conditions with respect to particles in the lower free troposphere and suggested a trapping of aerosol particles inside the boundary layer. Undisturbed transport of continental anthropogenic pollutants to remote regions was observed and a direct effect on the radiative properties of the aerosol population was found. 90% of the aerosol optical depth above the Atlantic southwest of Ireland was caused by the pollution layers, which originated from continental Europe. The analysis of air mass transport and ageing processes indicated that the main coagulation process of aerosol particles happens within the first 12–24 h. The saturation of the coagulation process occurred after two days.