Abstract
Abstract. Anthropogenic emissions in China play an important role in altering the global radiation budget. Over the past decade, the strong clean-air policies in China have resulted in substantial reductions of anthropogenic emissions of sulfur dioxide (SO2) and primary particulate matter, and air quality in China has consequently improved. However, the resultant aerosol radiative forcings have been poorly understood. In this study, we used an advanced global climate model integrated with the latest localized emission inventory to quantify the aerosol radiative forcings by the changes of anthropogenic emissions in China between 2008 and 2016. By comparing with multiple observation datasets, our simulations reproduced the considerable reductions of sulfate and black carbon (BC) mass loadings reasonably well over eastern China (the key region subject to stringent emission controls) during the period and accordingly showed a clear decline in both aerosol optical depth and absorption aerosol optical depth. The results revealed a regional annual mean positive direct radiative forcing (DRF) of +0.29 W m−2 at the top of the atmosphere (TOA) due to the reduction of SO2 emissions. This positive aerosol radiative forcing was comprised of diminished sulfate scattering (+0.58 W m−2), enhanced nitrate radiative effects (−0.29 W m−2), and could be completely offset by the concurrent reduction of BC emissions that induced a negative BC DRF of −0.33 W m−2. Despite the small net aerosol DRF (−0.05 W m−2) at the TOA, aerosol–radiation interactions could explain the surface brightening in China over the past decade. The overall reductions in aerosol burdens and associated optical effects mainly from BC and sulfate enhanced the regional annual mean downward solar radiation flux at the surface by +1.0 W m−2 between 2008 and 2016. The enhancement was in general agreement with a long-term observational record of surface energy fluxes in China. We also estimated that aerosol effects on cloud radiative forcings may have played a dominant role in the net aerosol radiative forcings at the TOA in China and over the northern Pacific Ocean during the study period. This study will facilitate more informed assessment of climate responses to projected emissions in the future as well as to sudden changes in human activities (e.g., the COVID-19 lockdown).
Highlights
Aerosols perturb the global energy balance through the scattering and absorption of sunlight (Charlson et al, 1992) and serve as cloud condensation nuclei (CCN) particles, which impact both the cloud albedo and cloud lifetime (Twomey, 1974; Andreae and Rosenfeld, 2008)
The uncertainties embedded in the radiative forcing (RF) of black carbon (BC) have been large because the treatment of BC atmospheric processes in climate models include the impacts of BC on liquid clouds (Koch and Del Genio, 2010; Chung and Seinfeld, 2002) and the role of BC acting as ice nuclei (Kulkarni et al, 2016) is impre
The sulfate concentrations simulated by the CAM5/ATRAS2 model generally agreed with available observations with respect to the magnitude and spatial patterns
Summary
Aerosols perturb the global energy balance through the scattering and absorption of sunlight (Charlson et al, 1992) and serve as cloud condensation nuclei (CCN) particles, which impact both the cloud albedo and cloud lifetime (Twomey, 1974; Andreae and Rosenfeld, 2008). The uncertainties embedded in the radiative forcing (RF) of BC have been large because the treatment of BC atmospheric processes in climate models include the impacts of BC on liquid clouds (Koch and Del Genio, 2010; Chung and Seinfeld, 2002) and the role of BC acting as ice nuclei (Kulkarni et al, 2016) is impre-. Sulfate aerosols are estimated to induce a global mean DRF of −0.32 W m−2 during the period from 1750–2010 (Myhre et al, 2013) and cause a remarkable radiative perturbation in the north mid-latitude region (20–40◦ N) because of the rapid increase of anthropogenic SO2 emissions in China over the past few decades. The tremendous anthropogenic emissions in China have resulted in severe air pollution and in a significant alteration of the global shortwave radiation budget (B. Li et al, 2016)
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