Linked Response of Aerosol Water Content and Acidity to Future Anthropogenic Emission Control over the North China Plain

Abstract

China’s air quality improvement and carbon neutrality goals will substantially reshape atmospheric gas and aerosol compositions through reduced emissions of acidic and alkaline precursors. However, the impacts of these goals on aerosol physicochemical properties, specifically the coupled responses of aerosol water content (AWC) and acidity (pH), remain poorly constrained. The North China Plain (NCP), with globally high AWC and pH and pivotal for implementing anthropogenic emission controls, was selected as the study area. Here, we simulated the long-term winter trends in AWC and aerosol pH across representative emission scenarios by utilizing the goddard earth observing system (GEOS)-Chem chemical transport model coupled with the ISORROPIA-II thermodynamic model. Results show that the aerosol mass growth factor remains relatively stable, with AWC decline mainly driven by reduced inorganic aerosol mass concentrations. Aerosol pH exhibits nonlinear spatiotemporal patterns across scenarios, reflecting a dynamic balance between two opposing mechanisms: (1) a trend toward increased acidity driven by the linked decrease in AWC and (2) a countervailing trend toward alkalinity due to rising alkali-to-acid ratios. Aqueous phase nonideality emerges as a critical but under-valued driver of long-term pH trajectories. This study establishes a mechanistic framework for disentangling the drivers of aerosol hygroscopicity and acidity, providing insights into atmospheric multiphase chemistry and emission mitigation strategies.