Gaseous Sulfuric\nAcid Contributions to Sulfate Formation\nin Urban Atmosphere

Sulfate aerosols are critical atmospheric constituents,\ninfluencing\nair quality and climate. Their complex formation processes have been\nstudied predominantly in the context of multiphase chemistry. However,\nthe substantial contribution of gas-phase condensation of sulfuric\nacid (SA<sub>cond</sub>) to sulfate aerosol formation has not been\nfully recognized, primarily due to the challenges associated with\nthe long-term measurement of gaseous sulfuric acid (H<sub>2</sub>SO<sub>4</sub>). Using the comprehensive data set from the SORPES station,\nwe elucidated the influence of gaseous H<sub>2</sub>SO<sub>4</sub> on sulfate aerosol generation across different meteorological and\npollution contexts. Our analysis indicates a marked increase in gaseous\nH<sub>2</sub>SO<sub>4</sub> concentrations enhances its role in sulfate\nformation, with cumulative five-day production accounting for up to\n50% of the total sulfate levels. Detailed analysis of stable meteorological\nconditions revealed that SA<sub>cond</sub> initially increases and\nthen stabilizes with higher levels of PM<sub>2.5</sub>, while its\nrelative influence on sulfate formation diminishes. This implies that\nin high-polluted environments, multiphase reactions primarily drive\nsulfate formation. Given the ongoing efforts to reduce PM<sub>2.5</sub> levels in China, the role of SA<sub>cond</sub> in shaping sulfate\naerosol profiles is anticipated to become increasingly significant.\nThis underscores the need for a renewed focus on gas-phase processes\nwithin the broader context of aerosol formation and atmospheric chemistry.