TY - JOUR

T1 - Inter-annual variations of wet deposition in Beijing from 2014-2017

T2 - Implications of below-cloud scavenging of inorganic aerosols

AU - Ge, B.

AU - Xu, D.

AU - Wild, O.

AU - Yao, X.

AU - Wang, J.

AU - Chen, X.

AU - Tan, Q.

AU - Pan, X.

AU - Wang, Z.

PY - 2021/6/22

Y1 - 2021/6/22

N2 - Wet scavenging is an efficient pathway for the removal of particulate matter (PM) from the atmosphere. High levels of PM have been a major cause of air pollution in Beijing but have decreased sharply under the Air Pollution Prevention and Control Action Plan launched in 2013. In this study, 4 years of observations of wet deposition have been conducted using a sequential sampling technique to investigate the detailed variation in chemical components through each rainfall event. We find that the major ions, SO42-, Ca2+, NO3-, and NH4+, show significant decreases over the 2013-2017 period (decreasing by 39g%, 35g%, 12g%, and 25g%, respectively), revealing the impacts of the Action Plan. An improved method of estimating the below-cloud scavenging proportion based on sequential sampling is developed and implemented to estimate the contribution of below-cloud and in-cloud wet deposition over the four-year period. Overall, below-cloud scavenging plays a dominant role to the wet deposition of four major ions at the beginning of the Action Plan. The contribution of below-cloud scavenging for Ca2+, SO42-, and NH4+ decreases from above 50g% in 2014 to below 40g% in 2017. This suggests that the Action Plan has mitigated PM pollution in the surface layer and hence decreased scavenging due to the washout process. In contrast, we find little change in the annual volume weighted average concentration for NO3- where the contribution from below-cloud scavenging remains at g1/4g44g% over the 2015-2017 period. While highlighting the importance of different wet scavenging processes, this paper presents a unique new perspective on the effects of the Action Plan and clearly identifies oxidized nitrogen species as a major target for future air pollution controls.

AB - Wet scavenging is an efficient pathway for the removal of particulate matter (PM) from the atmosphere. High levels of PM have been a major cause of air pollution in Beijing but have decreased sharply under the Air Pollution Prevention and Control Action Plan launched in 2013. In this study, 4 years of observations of wet deposition have been conducted using a sequential sampling technique to investigate the detailed variation in chemical components through each rainfall event. We find that the major ions, SO42-, Ca2+, NO3-, and NH4+, show significant decreases over the 2013-2017 period (decreasing by 39g%, 35g%, 12g%, and 25g%, respectively), revealing the impacts of the Action Plan. An improved method of estimating the below-cloud scavenging proportion based on sequential sampling is developed and implemented to estimate the contribution of below-cloud and in-cloud wet deposition over the four-year period. Overall, below-cloud scavenging plays a dominant role to the wet deposition of four major ions at the beginning of the Action Plan. The contribution of below-cloud scavenging for Ca2+, SO42-, and NH4+ decreases from above 50g% in 2014 to below 40g% in 2017. This suggests that the Action Plan has mitigated PM pollution in the surface layer and hence decreased scavenging due to the washout process. In contrast, we find little change in the annual volume weighted average concentration for NO3- where the contribution from below-cloud scavenging remains at g1/4g44g% over the 2015-2017 period. While highlighting the importance of different wet scavenging processes, this paper presents a unique new perspective on the effects of the Action Plan and clearly identifies oxidized nitrogen species as a major target for future air pollution controls.

KW - action plan

KW - aerosol

KW - annual variation

KW - atmospheric pollution

KW - cloud

KW - concentration (composition)

KW - nitrate

KW - particulate matter

KW - wet deposition

KW - Beijing [China]

KW - China

U2 - 10.5194/acp-21-9441-2021

DO - 10.5194/acp-21-9441-2021

M3 - Review article

VL - 21

SP - 9441

EP - 9454

JO - Atmospheric Chemistry and Physics

JF - Atmospheric Chemistry and Physics

SN - 1680-7316

IS - 12

ER -