Gaseous Sulfuric Acid Contributions to Sulfate Formation in Urban Atmosphere

Sulfate aerosols are critical atmospheric constituents, influencing air quality and climate. Their complex formation processes have been studied predominantly in the context of multiphase chemistry. However, the substantial contribution of gas-phase condensation of sulfuric acid (SAcond) to sulfate aerosol formation has not been fully recognized, primarily due to the challenges associated with the long-term measurement of gaseous sulfuric acid (H2SO4). Using the comprehensive data set from the SORPES station, we elucidated the influence of gaseous H2SO4 on sulfate aerosol generation across different meteorological and pollution contexts. Our analysis indicates a marked increase in gaseous H2SO4 concentrations enhances its role in sulfate formation, with cumulative five-day production accounting for up to 50% of the total sulfate levels. Detailed analysis of stable meteorological conditions revealed that SAcond initially increases and then stabilizes with higher levels of PM2.5, while its relative influence on sulfate formation diminishes. This implies that in high-polluted environments, multiphase reactions primarily drive sulfate formation. Given the ongoing efforts to reduce PM2.5 levels in China, the role of SAcond in shaping sulfate aerosol profiles is anticipated to become increasingly significant. This underscores the need for a renewed focus on gas-phase processes within the broader context of aerosol formation and atmospheric chemistry.