Volume 128, Issue 11 e2022JD038377
Research Article

Distinct Seasonality in Aerosol Responses to Emission Control Over Northern China

Yawen Liu

Yawen Liu

School of Atmospheric Sciences, Nanjing University, Nanjing, China

Joint International Research Laboratory of Atmospheric and Earth System Sciences & Institute for Climate and Global Change Research, Nanjing University, Nanjing, China

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Minghuai Wang

Corresponding Author

Minghuai Wang

School of Atmospheric Sciences, Nanjing University, Nanjing, China

Joint International Research Laboratory of Atmospheric and Earth System Sciences & Institute for Climate and Global Change Research, Nanjing University, Nanjing, China

Correspondence to:

M. Wang,

[email protected]

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Man Yue

Man Yue

Zhejiang Institute of Meteorological Sciences, Hangzhou, China

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Yun Qian

Yun Qian

Pacific Northwest National Laboratory, Richland, Washington, USA

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First published: 22 May 2023

Abstract

Despite intensive research exploring how aerosols respond to emission control over Northern China, efforts mostly focus on the environmental benefit, especially in winter. Here we found that unlike the most substantial PM2.5 concentration reduction in winter, aerosol optical depth (AOD) declines more than 2 times faster in summer, causing an increase in aerosol radiative effects of 1.2 (5.7)Wm−2 on all-sky (clear-sky) conditions over 2013–2019 and largely shaping the climate impact. Low-level aerosols are shown to be the prime contributor under the synergetic effects of aerosol composition and ambient relative humidity (RH). The dominance of the highly hygroscopic sulfate combined with high RH enables a strong extinction efficiency of the reduced summertime aerosols, while the insignificant AOD decline in wintertime result from the dominance of organic aerosols with weak hygroscopicity, and is further offset by the increased frequencies of extremely high RH. We show the environmental and climatic responses of aerosols to emission control exhibit distinctively different seasonality.

Key Points

  • Trends of aerosol concentrations and optical properties show different seasonality, with a larger decline in winter and summer separately

  • Changes in low-level aerosols below 1 km play a prime role under the synergetic effects of aerosol composition and relative humidity

  • Summertime aerosol changes cause an increase in aerosol radiative effects of 1.2 Wm−2 over 2013–2019, largely shaping the climate impact

Plain Language Summary

Although many efforts have been devoted to assessing the aerosol responses to emission reductions in Northern China, these efforts mostly focus on the environmental benefit, especially in winter. Here we examined the seasonal features of aerosol changes over 2013–2019 and found a distinct seasonality for trends of aerosol concentrations and optical properties. Unlike the most substantial PM2.5 concentration reduction in winter, aerosol optical depth (AOD) declines much faster in summer by a factor of 2–2.9 and causes an increase in aerosol radiative effects of 5.7 and 1.2  m−2 on clear and all-sky conditions. Low-level aerosols are shown to play the prime role. The highly hygroscopic sulfate, combined with the high ambient relative humidity (RH) leads to a strong extinction efficiency of the reduced summertime aerosols, which explains the remarkable AOD decline. Contrarily, changes in winter are dominated by organic aerosols (OA). Though the sharp reduction of primary OA emissions leads to a more prominent decline of PM2.5 concentrations in winter, the corresponding AOD decrease remains insignificant due to its weak hygroscopicity and is offset by the increasing frequency of extremely high RH conditions. Our work demonstrates the synergetic effects of aerosol composition and ambient RH on the distinctively different environmental and climatic responses of aerosols.

Data Availability Statement

All the data used in this study are archived in publicly accessible databases, and data sources are listed below. The GSOD visibility data is available at (https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00516; Smith et al., 2011). The TAP reanalysis data set can be found at http://tapdata.org.cn/?page_id=127&lang=en (Geng et al., 2021). MODIS AOD measurements can be obtained from https://search.earthdata.nasa.gov/search?q=MOD08&fl=3%2B-%2BGridded%2BObservations and https://search.earthdata.nasa.gov/search?q=MYD08&fl=3%2B-%2BGridded%2BObservations (Levy et al., 2013). The CERES radiative fluxes can be obtained from https://ceres.larc.nasa.gov/data/ (Loeb et al., 2018). MEIC emission data set is provided at http://meicmodel.org.cn/?page_id=2351&lang=en (Li et al., 2017). Figures were made with the NCAR Command Language version 6.6.2 (NCAR, 2019).