Intensive measurements were conducted in Xi'an,China before and during a COVID-19 lockdown period to investigate how changes in anthropogenic emissions affected the optical properties and radiative effects of brown carbon(BrC)aerosol.The contribution of BrC to total aerosol light absorption during the lockdown(13％-49％)was higher compared with the normal period(4％-29％).Mass absorption cross-sections(MACs)of specific organic aerosol(OA)factors were calculated from a ridge regression model.Of the primary OA(POA),coal combustion OA(CCOA)had the largest MACs at all tested wave-lengths during both periods due to high molecular-weight BrC chromophores;that was followed by bio-mass burning OA(BBOA)and hydrocarbon-like OA(HOA).For secondary OA(SOA),the MACs of the less-oxidized oxygenated OA(OOA)species(LO-OOA)at A,=370-590 nm were higher than those of more-oxidized OOA(MO-OOA)during both periods,presumably due to chromophore bleaching.The largest contributor to BrC absorption at the short wavelengths was CCOA during both periods,but BrC absorption by LO-OOA and MO-OOA became dominant at longer wavelengths during the lockdown.The estimated radiation forcing efficiency of BrC over 370-600 nm increased from 37.5 W-g-1 during the normal period to 50.2 W-g-1 during the lockdown,and that enhancement was mainly caused by higher MACs for both LO-OOA and MO-OOA.This study provides insights into the optical properties and radiative effects of source-specific BrC aerosol when pollution emissions are reduced.

Yong Zhang;Qiyuan Wang;Jie Tian;Yu Li;Huikun Liu;Weikang Ran;Yongming Han;André S.H.Prév?t;Junji Cao

State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710061,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Quaternary Science and Global Change,Xi'an 710061,China;Guanzhong Plain Ecological Environment Change and Comprehensive Treatment National Observation and Research Station,Xi'an 710061,China;Xi'an Institute for Innovative Earth Environment Research,Xi'an 710061,China;Laboratory of Atmospheric Chemistry,Paul Scherrer Institute(PSI),Villigen 5232,Switzerland

地学前缘（英文版）

[1]Yong Zhang;Qiyuan Wang;Jie Tian;Yu Li;Huikun Liu;Weikang Ran;Yongming Han;André S.H.Prév?t;Junji Cao-.Impact of COVID-19 lockdown on the optical properties and radiative effects of urban brown carbon aerosol)[J].地学前缘（英文版）,2022(06):291-301

MACs,CCOA,chromophore

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