Radiative Effects of Recent Changes in PM2.5 Pollution over China and Local and Remote Climate Impacts

Abstract

The large reduction in anthropogenic aerosol emissions across China in recent years has improved China’s air quality but also caused changes in radiative forcing. Some studies confirmed the reduction of aerosols over China cause a positive radiative forcing locally and play an important role in Arctic warming. However, few studies have differentiated and quantified the radiative forcing of different aerosol components including BC and sulphate. Here, we aim to understand the reduction of black carbon (BC) and SO2 emissions over China from 2008 to 2016 under a series of policies enacted by the Chinese government and to determine the change in radiative forcing both locally and remotely. We use the Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants (ECLIPSE) emission inventory to represent China's emissions of the two pollutants during this period and use the United Kingdom Earth System Model (UKESM) v-1 to calculate the individual radiative forcing due to changes in all anthropogenic aerosols, China BC only, and China SO2 only between 2008 and 2016. Finally, we use the temperature coefficients of individual pollutants at different latitude bands to calculate the temperature responses. Our results show the largest reduction of BC over China was from the residential and energy sectors, while the reduction in SO2 emissions from energy and industrial sources were significant. Compared with other inventories, ECLIPSE overestimates the reduction of emissions but shows the same trend. The aerosol radiative forcing over China locally due to the large Chinese emission reductions of BC and SO2 are -0.30±0.01Wm-2 and 1.03±0.07 Wm-2, respectively, which jointly accounts for more than 80% of the total aerosol radiative forcing calculated by the model from all anthropogenic aerosol emission sources. In addition, changes in BC and SO2 over China together contributed to a positive radiative forcing of 0.18 Wm-2 across the North Pacific. However, BC and sulphate are not major contributors to changes in Arctic radiative forcing. The temperature response due to BC (-0.008 ℃) and sulphate (0.060 ℃) is most pronounced locally in the mid-latitudes, while the temperature response in the low and high latitudes is small. This study bridges the gap on changes in radiative forcing due to anthropogenic emissions reductions in China and quantifies the contributions of BC and sulphate aerosols to better understand the impact of air pollution emission control policies on climate.