Intra-event evolution of elemental and ionic concentrations in wet deposition in an urban environment

Abstract. Wet deposition is a crucial process that affects the lifetime of atmospheric particles by allowing them to be deposited by two different mechanisms, namely below the cloud and in the cloud. In order to estimate the mechanisms implied in the wet deposition, a measurement campaign was carried out in the Paris region to monitor the evolution of the chemical composition of wet deposition during rainfall events. Eight rain events have been sampled. The latter had different meteorological conditions, atmospheric dynamics and aerosol particles concentrations. Concomitant measurements of the chemical composition of aerosol particles and wet deposition allows calculating washout ratios from measurements taken at the beginning of the rainfall events, before the dilution effect occurred, and showed an increasing trend with increasing rainfall rates. The intra-event evolution of the chemical composition of wet deposition revealed the predominant role of meteorological parameters and local sources in the observed mass concentration variability. The contributions of in-cloud and below-cloud scavenging mechanisms were estimated for some rainfall events and found to vary depending on the specific sources, atmospheric dynamics and meteorological conditions. Overall, this study highlights the variability of wet deposition and its chemical composition, and the need to consider the specificities of each event to fully understand the underlying mechanisms.