Heterogeneous Oxidation of SO2 in Sulfate Production during Nitrate Photolysis at 300 nm : Effect of pH, Relative Humidity, Irradiation Intensity, and the Presence of Organic Compounds

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalNot applicablepeer-review

2 Scopus Citations
View graph of relations

Author(s)

Related Research Unit(s)

Detail(s)

Original languageEnglish
Pages (from-to)8757-8766
Journal / PublicationEnvironmental Science and Technology
Volume53
Issue number15
Online published26 Jun 2019
Publication statusPublished - 6 Aug 2019

Abstract

Heterogeneous oxidation of SO2 is one of the promising mechanisms to account for high loading of sulfate during severe haze periods in China. Our earlier work reported on the SO2 oxidation by OH and NO2 produced during 250 nm nitrate photolysis (Environ. Sci. Technol. Lett. 2019, 6, 86-91). Here, we extend that work to examine sulfate production during nitrate photolysis at 300 nm irradiation, which can additionally generate NO2- or HNO2, N(III). Flow cell/in situ Raman experiments showed that the reactive uptake coefficient of SO2, γSO2, can be expressed as γSO2 = 1.64 × pNO3-, where pNO3- is the nitrate photolysis rate in the range of (1.0-8.0) × 10-5 M s-1. Our kinetic model with the pNO3- predicts that N(III) is the main contributor to the SO2 oxidation, followed by NO2 contribution. Furthermore, the addition of OH scavengers (e.g., glyoxal or oxalic acid) does not suppress the sulfate production because of the reduced N(III)-consuming reactions and the high particle pH sustained by their presence. Our calculations illustrate that under characteristic haze conditions, the nitrate photolysis mechanism can produce sulfate at ∼1 μg m-3 h-1 at pH 4-6 and pNO3- = 10-5 M s-1. The present study highlights the importance of in-particle nitrate photolysis in heterogeneous oxidation of SO2 by reactive nitrogen (NO2-/HNO2 and NO2) under atmospherically relevant actinic irradiation. However, the nitrate photolysis rate constant needs to be better constrained for ambient aerosols.

Citation Format(s)

Heterogeneous Oxidation of SO2 in Sulfate Production during Nitrate Photolysis at 300 nm : Effect of pH, Relative Humidity, Irradiation Intensity, and the Presence of Organic Compounds. / Gen, Masao; Zhang, Ruifeng; Huang, Dan Dan; Li, Yongjie; Chan, Chak K.

In: Environmental Science and Technology, Vol. 53, No. 15, 06.08.2019, p. 8757-8766.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalNot applicablepeer-review