Synergistic effect among Cl2, SO2 and NO2 in their heterogeneous reactions on gamma-alumina

- Cl2, NO2 and SO2 have synergistic effects when they react with the surface of γ-Al2O3.
- The presence of γ-Al2O3 seed aerosols greatly promotes the formation of secondary inorganic aerosols.
- Cl2 can promote the formation of secondary sulfate and nitrate aerosols on γ-Al2O3 surface.
- The possible heterogeneous reaction mechanism of Cl2, NO2 and SO2 on γ-Al2O3 surface are proposed.

Severe haze in China has been a global concern in recent years. Most studies about the mechanism of haze formation mare only focused on the heterogeneous reactions of SO2 and NO2 on mineral aerosols. However, little is known about the role of molecular chlorine (Cl2) in those reactions. Here, we investigated the heterogeneous uptake of Cl2, SO2 and NO2 on γ-Al2O3 particles under different conditions using a quartz-based flow reactor. We found that the existence of γ-Al2O3 seed aerosols significantly promotes the formation of secondary chloride, sulfate and nitrate aerosols, and Cl2, NO2 and SO2 have synergistic effects when they react on γ-Al2O3 surface under humid condition. The results also shows that Cl2 can promote the formation of secondary sulfate and nitrate aerosols on γ-Al2O3 surface. Moreover, Cl2 is much easier to react with the surface of γ-Al2O3 and form secondary Cl− aerosol when comparing with NO2 and SO2, suggesting that Cl2 is of great importance in atmospheric chemistry, it has the potential to alter the surface properties (e.g., chemical composition and fraction) of mineral aerosol, enhance the production of secondary inorganic aerosols in the troposphere, and thus cause adverse effects on the climate and human health.