Sulfate Formation Apportionment during Winter Haze Events in North China

Abstract

There is a large gap between the simulated and observed sulfate concentrations during winter haze events in North China. Although multiphase sulfate formation mechanisms have been proposed, they have not been evaluated using chemical transport models. In this study, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) was used to apportion sulfate formation. It was found that Mncatalyzed oxidation on aerosol surfaces was the dominant sulfate formation pathway, accounting for 92.3 ± 3.5% of the sulfate formation during haze events. Gas-phase oxidation contributed 3.1 ± 0.5% to the sulfate formation due to the low OH levels. The H 2 O 2 oxidation in aerosol water accounted for 4.2 ± 3.6% of the sulfate formation, caused by the rapid consumption of H 2 O 2 . The contributions of O 3 , NO 2 oxidation, and transition metal ion-catalyzed reactions in aerosol water could be negligible owing to the low aerosol water content, low pH, and high ionic strength. The contributions from in-cloud reactions were negligible due to the barrier provided by stable stratification during winter haze events.

Role of Dust and Iron Solubility in Sulfate Formation during the Long-Range Transport in East Asia Evidenced by 17O-Excess Signatures

“…This interpretation is consistent with previous studies, which proposed these mechanisms as missing processes in Chinese haze. 17 , 18 , 24 − 26 It is worthy to conclude that AQ(H 2 O 2 ) does not explain this missing SO 4 2– formation during February.…”

“…For example, while the importance of NO 2 for SO within the aerosol surface was proposed, 17 follow-up studies have cast doubt on the impact of its reaction. 25,26 Thus, these proposed reactions have been highly controversial arguments. These pollution and haze events over China and their impact on the downstream region should be mitigated, mainly via the reduction of anthropogenic SO 2 emissions.…”

“…For example, while the importance of NO 2 for SO 4 2– formation within the aerosol surface was proposed, 17 follow-up studies have cast doubt on the impact of its reaction. 25 , 26 Thus, these proposed reactions have been highly controversial arguments.…”

“…However, typical CTMs often underestimate the burden of atmospheric SO 4 2– , particularly in China, , suggesting that some SO 4 2– formation in the atmosphere is missing. To date, heterogeneous SO 4 2– production mechanisms particularly for aerosol surfaces − have been proposed to explain this missing formation such as the enhanced role of the oxidation by reactive nitrogen, − H 2 O 2 , TMI-catalyzed O 2 , − and Mn-catalyzed oxidation. , Nonetheless, the observational evidence has not yet identified a specific mechanism. For example, while the importance of NO 2 for SO 4 2– formation within the aerosol surface was proposed, follow-up studies have cast doubt on the impact of its reaction. , Thus, these proposed reactions have been highly controversial arguments.…”

“…To date, heterogeneous SO 4 2– production mechanisms particularly for aerosol surfaces − have been proposed to explain this missing formation such as the enhanced role of the oxidation by reactive nitrogen, − H 2 O 2 , TMI-catalyzed O 2 , − and Mn-catalyzed oxidation. , Nonetheless, the observational evidence has not yet identified a specific mechanism. For example, while the importance of NO 2 for SO 4 2– formation within the aerosol surface was proposed, follow-up studies have cast doubt on the impact of its reaction. , Thus, these proposed reactions have been highly controversial arguments.…”