Formation of aqueous-phase sulfate during the haze period in China: Kinetics and atmospheric implications

Sulfate is one of the most important components in the aerosol due to its key role in air pollution and global climate change. Recent work has suggested that reactive nitrogen chemistry in aqueous water can explain the missing source of sulfate in the aqueous water. Herein, we have mapped out the energy profile of the oxidization process of SO₂ leading from NO₂ and two feasible three-step mechanisms have been proposed. For the oxidation of HOSO₂⁻ and HSO₃⁻ by the dissolved NO₂ in weakly acidic and neutral aerosol (pH ≤ 7), the main contribution to the missing sulfate production comes from the oxidation of HOSO₂⁻. The whole process is a self-sustaining process. For the oxidation of SO₃²⁻ in alkaline aerosol (pH > 7), the third step - decomposition step of H₂O or hydrolysis of SO₃ step which are two parallel processes are the rate-limiting steps. The present results are of avail to better understand the missing source of sulfate in the aerosol and hence may lead to better science-based solutions for resolving the severe haze problems in China.