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Key role of pH in the photochemical conversion of NO2 to HONO on humic acid
AbstractThe heterogeneous photochemical reactions of NO2 with humic acid (HA) were performed using a flow tube reactor coupled to a NOx analyzer. The effects of the pH on the uptake coefficient (γ) of NO2 and HONO and NO yields were investigated in detail. With increasing the pH in the range of 2–12, γ was almost constant with an average value of (4.21 ± 0.46) × 10−6, whereas the HONO yield and NO yield linearly decreased from (81.07 ± 4.07)% and (10.35 ± 3.86)% to (13.87 ± 9.15)% and (1.51 ± 0.94)%, respectively. According to the characterization of HA compositions and possible reaction paths, it can be concluded that the pH may influence the transfer of protons and the equilibrium of HONO with NO2− by varying the contents of carboxyl and phenol groups in HA, which should primarily contribute to the change in the HONO yield with the pH.
HighlightsThe γ of NO2 on HA almost remained unchanged with increasing the pH.There was a negatively linear dependence trend of the HONO yield on the pH.The contents of carboxyl and phenol in HA significantly decreased with the pH.Key role of pH in the HONO yield was related to its effects on the HA composition.
Key role of pH in the photochemical conversion of NO2 to HONO on humic acid
AbstractThe heterogeneous photochemical reactions of NO2 with humic acid (HA) were performed using a flow tube reactor coupled to a NOx analyzer. The effects of the pH on the uptake coefficient (γ) of NO2 and HONO and NO yields were investigated in detail. With increasing the pH in the range of 2–12, γ was almost constant with an average value of (4.21 ± 0.46) × 10−6, whereas the HONO yield and NO yield linearly decreased from (81.07 ± 4.07)% and (10.35 ± 3.86)% to (13.87 ± 9.15)% and (1.51 ± 0.94)%, respectively. According to the characterization of HA compositions and possible reaction paths, it can be concluded that the pH may influence the transfer of protons and the equilibrium of HONO with NO2− by varying the contents of carboxyl and phenol groups in HA, which should primarily contribute to the change in the HONO yield with the pH.
HighlightsThe γ of NO2 on HA almost remained unchanged with increasing the pH.There was a negatively linear dependence trend of the HONO yield on the pH.The contents of carboxyl and phenol in HA significantly decreased with the pH.Key role of pH in the HONO yield was related to its effects on the HA composition.
Key role of pH in the photochemical conversion of NO2 to HONO on humic acid
Han, Chong (author) / Yang, Wangjin (author) / Wu, Qianqian (author) / Yang, He (author) / Xue, Xiangxin (author)
Atmospheric Environment ; 142 ; 296-302
2016-07-27
7 pages
Article (Journal)
Electronic Resource
English
Photochemical aspects related to humic substances
| Online Contents | 1994
Photochemical aspects related to humic substances
| Elsevier | 1994