Schmücke hill cap cloud and valley stations aerosol characterisation during FEBUKO (I): Particle size distribution, mass, and main components

Abstract

Hill cap cloud field experiments were performed during autumn 2001 and 2002 in the Thüringer Wald (Germany). Gas phase trace compounds were determined at an upwind, summit, and downwind sites and major particulate components at an upwind and downwind site. Cloud water and total cloud components (drop residuals and interstitial particles) were determined at a summit site. Three events were fulfilling the criteria for the best conditions defined by during a connected flow upwind–summit–downwind sites and further detailed analysis was performed on these events. Cloud water components were compared with particle concentration at upwind and downwind site. The concentrations of non-volatile components in cloud water were found to be in good agreement with corresponding particle phase concentrations at the upwind site. Downwind site particulate component concentrations of non-volatile compounds were lower than in cloud water indicating loss processes during transport such as deposition. The concentrations of volatile components were found to be higher in cloud water than in the particle phase concentrations at up- and downwind site samples probably due to a loss from impactor sampling technique as well as a transport loss. Indications for changes of aerosol composition by cloud processes were found from a limited number of cases. Elevated sulphate and ammonium concentrations from upwind to downwind site in the smallest particle size range (PM0.05–0.14) were found during event I (20% and 17%) and event III (70% and 150%), respectively. In the particle size range of PM0.14–0.42 an increase of OC by about 20% for event I was observed. Considering the relative contributions of components to the single size range mass (avoiding physical sink processes), comparatively higher increases for sulphate, nitrate, ammonium, OC, and EC could be observed. Indications of an increase of aerosol mass can be derived in some cases from the aerosol number and volume size distributions. Results from a complex multiphase model (SPACCIM) are consistent showing an increase in concentrations of some compounds for some cases.