Atmospheric HONO formation during and after the Spring Festival holidays in a coastal city of China
Jun Zhao , Xue Ni , Cuizhi Sun , Yongyun Zhang , Baoling Liang , Shengzhen Zhou , Guangdong Lan
DOI:10.1016/j.jes.2022.05.043
Received February 21, 2022,Revised , Accepted May 23, 2022, Available online June 03, 2022
Volume 35,2023,Pages 251-263
Nitrous acid (HONO) is an important source of hydrogen oxides (HOx), which affects air quality, the atmospheric oxidation capacity, and human health. Here, we present ambient measurements of the HONO concentrations in Zhuhai, a coastal city in Southern China, from February 7 to March 15, 2021. The campaign was classified into two periods during (P1) and after (P2) the Spring Festival holidays. The average HONO mixing ratio during P2 (1.19 ± 0.85 ppbv) was much higher than that during P1 (0.24 ± 0.18 ppbv), likely due to the contribution of homogeneous HONO formation. During nighttime, the heterogeneous conversion rate during P2 (0.0089/hr) was considerably higher than that during P1 (0.0057/hr), suggesting a higher heterogeneous NO2 conversion potential. However, the heterogeneous NO2 conversion was the dominant way during P1 with a high percentage of 88%, while comparable ratios of heterogeneous and homogeneous formation were found (54% vs. 46%) during P2, indicating that the homogeneous formation was also important during P2. During daytime, homogeneous reaction was the major known pathway, with a contribution of 16% during P1 and 27% during P2, leaving large unknown HONO sources which reasonably correlated with the photo-enhanced NO2 conversion. Two case scenarios were additionally explored, showing that there might be a primary emission source during one scenario (February 17-18) and vehicle emissions might be the major unknown HONO source for another scenario (March 3–5). The results suggest that large unknown daytime sources still exist which need more future ambient and laboratory studies.
