Dust pollution substantially weakens the impact of ammonia emission reduction on particulate nitrate formation

Abstract

Dust emissions significantly influence air quality and contribute to nitrate aerosol pollution by altering aerosol acidity. Understanding how dust interacts with ammonia emission controls is crucial for managing particulate nitrate pollution, especially in urban environments. In this study, we conducted field measurements of aerosol chemical components and gases across three cities in eastern China during the spring of 2023. By combining an aerosol thermodynamic model with machine learning, we assessed the relative contribution of dust to aerosol pH and its impact on nitrate formation. Our results show that changes in ammonia, in both the gas and particle phases, were the main factors affecting aerosol pH, with dust particles contributing to about 7 % of the total pH variation. During dust events, high concentrations of non-volatile ions increased aerosol pH, leading to higher nitrate levels in the particle phase. Machine learning analysis revealed that extreme dust storms caused a significant change in aerosol pH, enhancing nitrate partitioning. Further simulations indicated that while reducing ammonia emissions is effective in lowering nitrate levels under normal conditions, this effect is significantly reduced in dust-affected environments. Dust particles act as a buffer, reducing the sensitivity of nitrate formation to ammonia emission reductions. These findings emphasize the need to consider dust pollution when designing strategies for controlling particulate nitrate levels and highlight the complex interactions between dust and anthropogenic emissions.