PNNL

Abstract

Since China implemented the air pollution prevention and control action in 2013, the emissions of aerosols and precursors in East Asia have been greatly reduced, while emissions in South Asia have continued to increase, which form a dipole pattern of aerosol emissions between South Asia and East Asia. Here, the East Asian summer monsoon (EASM) responses to the dipole changes in aerosol emissions during 2013–2017 are investigated using the Community Earth System Model version 2 (CESM2). Decreases in East Asian emissions lead to a positive aerosol effective radiative forcing (ERF) anomaly of 1.59 W m-2 over central-eastern China (25°–40°N, 105°–122.5°), along with a 0.09? warming in summer during 2013–2017, which intensified the land-sea thermal contrast and caused the increase in rainfall by 0.32 mm day-1 over central-eastern China. When considering both the emission reductions in East Asia and increases in South Asia, the ERF anomaly is increased to 3.39 W m-2, along with an enhanced warming of 0.20? over central-eastern China. This is found to be the result of westward shift of the strengthened Western Pacific subtropical high (WPSH), linked to the increase in black carbon aerosol in South Asia. Based on multiple EASM indices, the reductions in aerosol emissions from East Asia alone during 2013–2017 increased the EASM strength by less than 5%, while the dipole changes in emissions together increased the EASM by 5–15% during 2013–2017, revealing an important role of South Asian aerosols in changing the East Asian climate.