Inter-annual variations of wet deposition in Beijing from 2014–2017: implications of below-cloud scavenging of inorganic aerosols

Abstract. Wet scavenging is an efficient pathway for the removal of particulate matter (PM) from atmosphere. High levels PM have been a major cause air pollution in Beijing but decreased sharply under Air Pollution Prevention and Control Action Plan launched 2013. In this study, 4 years observations wet deposition conducted using sequential sampling technique to investigate detailed variation chemical components through each rainfall event. We find that ions, SO42-, Ca2+, NO3-, NH4+, show significant decreases over 2013–2017 period (decreasing by 39 %, 35 12 25 respectively), revealing impacts Plan. An improved method estimating below-cloud proportion based on developed implemented estimate contribution in-cloud four-year period. Overall, plays dominant role four ions at beginning The NH4+ above 50 % 2014 below 40 2017. This suggests has mitigated surface layer hence due washout process. contrast, we little change annual volume weighted average concentration NO3- where remains ? 44 2015–2017 While highlighting importance different processes, paper presents unique new perspective effects clearly identifies oxidized nitrogen species as target future controls.