Source Contributions to and Effects of Aerosol Acidity on the Composition of Atmospheric Aerosols

Description

Atmospheric aerosols are of huge concern to policymakers worldwide due to their adverse environmental and health effects. Formulating air quality policies to reduce aerosol pollution based on current atmospheric models is challenging due to knowledge gaps on how the mass concentration and composition of aerosols evolve in the atmosphere. Aerosol acidity, which is described by the pH of an aqueous aerosol distribution, is an important property that regulates many atmospheric processes that transform aerosol mass concentration and composition. However, the effect of aerosol pH on atmospheric processes remain poorly constrained, which limits the capability of atmospheric models to explicitly consider aerosol acidity and assess its influence on aerosol mass concentration and composition.The proposed research aims to provide new insights into the contributions of emission sources to ambient aerosol acidity, and into the influence of aerosol acidity on various processes that transform aerosol mass concentrations and composition. We will first determine the pH of ambient aerosols in Hong Kong, and investigate the contributions of emission sources and their seasonal variations to aerosol pH. Aerosols will be collected on filters at City University of Hong Kong (CityU) during different seasons in a yearlong study. Different analytical techniques will be used to identify and quantify major aerosol constituents. Ambient aerosol pH values will be determined using a thermodynamic model with the measured aerosol constituents and meteorological conditions as model inputs. Positive matrix factorization analysis will be performed on the measured aerosol constituents to identify and quantify the individual contributions of different sources. A comprehensive statistical analysis of these datasets will then be performed to quantify the contributions of different sources to ambient aerosol pH, and to determine how these source contributions to aerosol pH change with the season. We will also conduct additional ambient measurements at the same site and similar thermodynamic modeling studies to investigate the extent to which aerosol acidity promotes the water-solubility of different metals in ambient aerosols. Lastly, we will conduct laboratory aerosol oxidation experiments on collected ambient aerosol samples and laboratory-generated model aerosols to investigate the influence of aerosol acidity on the chemical transformation of aqueous organic aerosols through heterogeneous hydroxyl (OH) radical photooxidation. Overall, the successful implementation of this proposal will fill critical knowledge gaps on the role of aerosol acidity in atmospheric processes that transform aerosol mass concentration and composition, which is crucial for the improvement of atmospheric models used in air quality policy formulation.