Observed coupling between air mass history, secondary growth of nucleation mode particles and aerosol pollution levels in Beijing.

S Hakala,L Dada,K R Dällenbach,J Kujansuu,J Kangasluoma,P Paasonen,Y Liu,L Wang,M Kulmala,V Vakkari,C Yan,Y Fu,T Petäjä,J Jiang,F Bianchi,C Deng

doi:10.1039/d1ea00089f

Abstract

Atmospheric aerosols have significant effects on the climate and on human health. New particle formation (NPF) is globally an important source of aerosols but its relevance especially towards aerosol mass loadings in highly polluted regions is still controversial. In addition, uncertainties remain regarding the processes leading to severe pollution episodes, concerning e.g. the role of atmospheric transport. In this study, we utilize air mass history analysis in combination with different fields related to the intensity of anthropogenic emissions in order to calculate air mass exposure to anthropogenic emissions (AME) prior to their arrival at Beijing, China. The AME is used as a semi-quantitative metric for describing the effect of air mass history on the potential for aerosol formation. We show that NPF events occur in clean air masses, described by low AME. However, increasing AME seems to be required for substantial growth of nucleation mode (diameter < 30 nm) particles, originating either from NPF or direct emissions, into larger mass-relevant sizes. This finding assists in establishing and understanding the connection between small nucleation mode particles, secondary aerosol formation and the development of pollution episodes. We further use the AME, in combination with basic meteorological variables, for developing a simple and easy-to-apply regression model to predict aerosol volume and mass concentrations. Since the model directly only accounts for changes in meteorological conditions, it can also be used to estimate the influence of emission changes on pollution levels. We apply the developed model to briefly investigate the effects of the COVID-19 lockdown on PM2.5 concentrations in Beijing. While no clear influence directly attributable to the lockdown measures is found, the results are in line with other studies utilizing more widely applied approaches.

Highlights

Despite ongoing pollution control measures, serious haze episodes with adverse health effects remain problematic in Beijing, China.1–3 The haze episodes are periods with elevated concentrations of aerosol particles in the accumulation mode size range, which are large enough to affect visibility by scattering and absorbing solar aAerosol and Haze Laboratory, Beijing Advanced Innovation Center for So Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China bInstitute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland
In this study, we investigate the evolution of aerosol number size distribution, aerosol volume concentration and PM2.5 as a function of air mass exposure to anthropogenic emissions (AME) in Beijing during the years 2018–2020
Our results point towards important roles of the nucleation mode particles, formed in NPF events or emitted from primary sources, and secondary aerosol formation in the development of pollution episodes

Summary

Introduction

Despite ongoing pollution control measures, serious haze episodes with adverse health effects remain problematic in Beijing, China. The haze episodes are periods with elevated concentrations of aerosol particles in the accumulation mode size range (particle diameter 100 nm–1 mm), which are large enough to affect visibility by scattering and absorbing solar aAerosol and Haze Laboratory, Beijing Advanced Innovation Center for So Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China bInstitute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland. CFinnish Meteorological Institute, Erik Palmenin Aukio 1, Helsinki, Finland dAtmospheric Chemistry Research Group, Chemical Resource Bene ciation, NorthWest University, Potchefstroom, South Africa eExtreme Environments Research Laboratory, Ecole Polytechnique Federale de Lausanne (EPFL) Valais, Sion, 1951, Switzerland fLaboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland gState Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China hJoint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing, China iState Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China † Electronic supplementary information (ESI) available.

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