TY - JOUR
T1 - O2-Mediated Synergistic Oxidation of Aqueous Bisulfite and Nitrite
T2 - A Key Pathway for Sulfate and Nitrate Formation in Atmospheric Sulfur-Nitrogen Cycles
AU - Zhang, Chunyan
AU - Liu, Jiarong
AU - Cao, Qing
AU - Chen, Tianzeng
AU - Wang, Yonghong
AU - Zhang, Peng
AU - Li, Hao
AU - Chu, Biwu
AU - Zhang, Xiuhui
AU - Ma, Qingxin
AU - He, Hong
N1 - Publisher Copyright:
© 2026 American Chemical Society
PY - 2026/4/14
Y1 - 2026/4/14
N2 - The coupled chemical transformation of NOx and SO2 plays a pivotal role in the atmospheric sulfur and nitrogen cycles. While these pollutants show negligible gas-phase interrelationship, they exhibit strong synergistic interactions in multiphase aerosol chemistry, yet their underlying reaction mechanisms remain elusive. We demonstrate that O2 serves as the key mediator enabling efficient coupling between aqueous-phase bisulfite (S(IV)) and nitrite (N(III)) through a previously overlooked reaction pathway at environmentally relevant pH (3.0–6.0). Under isolated conditions at pH 4.4, S(IV) undergoes sluggish O2-driven oxidation (4% sulfate yield), whereas N(III) remains oxidation-resistant. In the absence of O2, S(IV)-N(III) redox reactions yield limited sulfate (4%) and N2O, which is consistent with traditional mechanism cognition. Strikingly, the presence of O2 dramatically enhances co-oxidation, simultaneously producing sulfate (43%) and nitrate (36%). Theoretical calculations identify •HSO3 radicals (from HSO3-[jls-end-space/]/O2 interaction) as key intermediates that combine with O2/NO2- to form transient complexes ([•SO5···ONOH]− and [SO3-NO2···•HO2]−), which ultimately decompose into sulfate and nitrate. Observations in Beijing highlight the dominant role of the S(IV)-N(III) synergistic oxidation mechanism in sulfate formation, surpassing the conventional NO2- and O3-driven pathways. This breakthrough enhances our knowledge of atmospheric chemistry, particularly in the coupled cycling of sulfur and nitrogen, including sulfate/nitrate generation and HONO removal dynamics.
AB - The coupled chemical transformation of NOx and SO2 plays a pivotal role in the atmospheric sulfur and nitrogen cycles. While these pollutants show negligible gas-phase interrelationship, they exhibit strong synergistic interactions in multiphase aerosol chemistry, yet their underlying reaction mechanisms remain elusive. We demonstrate that O2 serves as the key mediator enabling efficient coupling between aqueous-phase bisulfite (S(IV)) and nitrite (N(III)) through a previously overlooked reaction pathway at environmentally relevant pH (3.0–6.0). Under isolated conditions at pH 4.4, S(IV) undergoes sluggish O2-driven oxidation (4% sulfate yield), whereas N(III) remains oxidation-resistant. In the absence of O2, S(IV)-N(III) redox reactions yield limited sulfate (4%) and N2O, which is consistent with traditional mechanism cognition. Strikingly, the presence of O2 dramatically enhances co-oxidation, simultaneously producing sulfate (43%) and nitrate (36%). Theoretical calculations identify •HSO3 radicals (from HSO3-[jls-end-space/]/O2 interaction) as key intermediates that combine with O2/NO2- to form transient complexes ([•SO5···ONOH]− and [SO3-NO2···•HO2]−), which ultimately decompose into sulfate and nitrate. Observations in Beijing highlight the dominant role of the S(IV)-N(III) synergistic oxidation mechanism in sulfate formation, surpassing the conventional NO2- and O3-driven pathways. This breakthrough enhances our knowledge of atmospheric chemistry, particularly in the coupled cycling of sulfur and nitrogen, including sulfate/nitrate generation and HONO removal dynamics.
KW - atmospheric oxidizing capacity
KW - haze chemistry
KW - secondary aerosol
KW - synergistic oxidation
UR - https://www.scopus.com/pages/publications/105035680989
U2 - 10.1021/acs.est.5c18609
DO - 10.1021/acs.est.5c18609
M3 - Article
C2 - 41914620
AN - SCOPUS:105035680989
SN - 0013-936X
VL - 60
SP - 10950
EP - 10960
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 14
ER -