TY - JOUR
T1 - Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics
AU - Wang, Yalin
AU - Huang, Dan Dan
AU - Huang, Wanyi
AU - Liu, Ben
AU - Chen, Qi
AU - Huang, Rujin
AU - Gen, Masao
AU - Mabato, Beatrix Rosette Go
AU - Chan, Chak K.
AU - Li, Xue
AU - Hao, Tianwei
AU - Tan, Yunkai
AU - Hoi, Ka In
AU - Mok, Kai Meng
AU - Li, Yong Jie
N1 - Generated from Scopus record by KAUST IRTS on 2023-07-06
PY - 2021/12/7
Y1 - 2021/12/7
N2 - A prominent source of hydroxyl radicals (•OH), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO2-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol,n-butanol, or formate as•OH scavengers, the average intrinsic quantum yield of nitrite [Φ(NO2-)] was 0.75 ± 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Φ(NO2-) was strongly pH-dependent, reaching 8.0 ± 2.1% at a pH of 8 and 1.5 ± 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO2for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments.
AB - A prominent source of hydroxyl radicals (•OH), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO2-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol,n-butanol, or formate as•OH scavengers, the average intrinsic quantum yield of nitrite [Φ(NO2-)] was 0.75 ± 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Φ(NO2-) was strongly pH-dependent, reaching 8.0 ± 2.1% at a pH of 8 and 1.5 ± 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO2for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments.
UR - https://pubs.acs.org/doi/10.1021/acs.est.1c04642
UR - http://www.scopus.com/inward/record.url?scp=85119951478&partnerID=8YFLogxK
U2 - 10.1021/acs.est.1c04642
DO - 10.1021/acs.est.1c04642
M3 - Article
SN - 1520-5851
VL - 55
SP - 15694
EP - 15704
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 23
ER -