AI Article Synopsis
- HONO is a key reactive nitrogen component and its sources and removal mechanisms are still not well understood, prompting a study in Xi'an and Xianyang from May 18-31, 2018.
- HONO mixing ratios were found to be similar in both cities, with notable differences in daytime and nighttime levels, revealing that heterogeneous processes significantly contribute to HONO formation, especially in Xianyang.
- The study highlights unknown daytime HONO formation processes and emphasizes the importance of local emissions and transport effects on air pollution in the Guanzhong area.
Article Abstract
HONO is an important component of reactive nitrogen (N) and precursors of OH radical. However, the source and removal of HONO are not clear. Here, measurements of HONO (May 18-31, 2018) were conducted in Xi'an and Xianyang simultaneously for the first time. The relationship between HONO and other N (such as NO and NO) in two cities was analyzed. The mixing ratio of HONO in Xi'an was 1.2 ± 0.8 ppbv, and that in Xianyang was 1.2 ± 1.1 ppbv. The nighttime HONO mixing ratio was higher in Xianyang, while the daytime HONO was higher in Xi'an. Compared with the contribution from heterogeneous process of NO, direct emissions and homogeneous processes (NO + OH) were less important for nocturnal HONO formation in these two cities. The relative contribution of heterogeneous process in Xianyang was more important than that in Xi'an. The reaction of NO upon aerosols surface was identified as an important source of HONO for two sites. The conversion of NO on the other surfaces might attend the heterogeneous formation of HONO in Xianyang site. Daytime HONO budget analysis indicated that there was an additional unknown formation process of HONO at two sites. The net OH production rate from HONO (from 08:00 to 17:00) was 1.6 × 10 and 1.3 × 10 molecule/(cm s) for Xian and Xianyang, 5.2 and 3.5 times higher than from O photolysis. Besides, a dust storm appeared during this observation period, and the impact of local emission and transport processes was separately analyzed. The sources, characteristics, and effects of HONO identified in this study laid a foundation for further research on HONO and air pollution in the Guanzhong area.
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| http://dx.doi.org/10.1016/j.envpol.2021.117679 | DOI Listing |
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