Modeling the Global\nImpact of Chlorine Chemistry on\nSecondary Organic Aerosols

Simulation of secondary organic aerosol (SOA) in models\nhas been\nan uncertain component in determining the impacts of atmospheric aerosols\non air quality and climate. Recent studies have shown that reactive\nchlorine can rapidly oxidize volatile organic compounds (VOCs), trigger\nSOA formation, and alter other oxidants, thus having a potentially\nsignificant effect on SOA, which has not been thoroughly investigated\nat the global scale. Here, we developed a chlorine-SOA simulation\nwithin a global chemical transport model along with updated anthropogenic\ncontinental chlorine emissions. Our simulations demonstrate that chlorine\nchemistry increases the annual mean boundary layer SOA by 5–12%\nover most continents while decreasing SOA by 5–11% over northern\nAtlantic and Pacific oceans, which are in the right direction to narrow\nexisting discrepancies between models and observations. Notably, sensitivity\nsimulations in China with observed high chlorine levels capture the\ntemporal variations of both observed fine Cl<sup>–</sup> and\norganic aerosol, showing an increase in SOA by more than 100%. Our\nstudy also reveals that polluted regions, which have ample emissions\nof both chlorine species and VOCs, exhibit potential chlorinated SOA,\nwhich are commonly toxic, contributing up to 15% to total SOA.