Chen Dongyang, Zhou Li, Liu Song, Lian Chaofan, Wang Weigang, Liu Hefan, Li Chunyuan, Liu Yuelin, Luo Lan, Xiao Kuang, Chen Yong, Qiu Yang, Tan Qinwen, Ge Maofa, Yang Fumo
College of Architecture and Environment, Sichuan University, Chengdu 610065, China; College of Carbon Neutrality Future Technology, Sichuan University, Chengdu 610065, China; Sichuan University Yibin Park, Yibin Institute of Industrial Technology, Yibin 644600, China.
College of Architecture and Environment, Sichuan University, Chengdu 610065, China; College of Carbon Neutrality Future Technology, Sichuan University, Chengdu 610065, China; Sichuan University Yibin Park, Yibin Institute of Industrial Technology, Yibin 644600, China.
Sci Total Environ. 2023 Dec 10;903:166605. doi: 10.1016/j.scitotenv.2023.166605. Epub 2023 Aug 26.
Nitrous acid (HONO) is an established precursor of hydroxyl (OH) radical and has significant impacts on the formation of PM and O. Despite extensive research on HONO observation in recent years, knowledge regarding its sources and sinks in urban areas remains inadequate. In this study, we monitored the atmospheric concentrations of HONO and related pollutants, including gaseous nitric acid and particulate nitrate, simultaneously at a supersite in downtown Chengdu, a megacity in southwestern China during spring, when was chosen due to its tolerance for both PM and O pollution. Furthermore, we employed the random forest model to fill the missing data of HONO, which exhibited good predictive performance (R = 0.96, RMSE = 0.36 ppbv). During this campaign, the average mixing ratio of HONO was measured to be 1.0 ± 0.7 ppbv. Notably, during periods of high O and PM concentrations, the mixing ratio of HONO was >50 % higher compared to the clean period. We developed a comprehensive parameterization scheme for the HONO budget, and it performed well in simulating diurnal variations of HONO. Based on the HONO budget analysis, we identified different mechanisms that dominate HONO formation at different times of the day. Vehicle emissions and NO heterogeneous conversions were found to be the primary sources of HONO during nighttime (21.0 %, 30.2 %, respectively, from 18:00 to 7:00 the next day). In the morning (7:00-12:00), NO heterogeneous conversions and the reaction of NO with OH became the main sources (35.0 %, 32.2 %, respectively). However, in the afternoon (12:00-18:00), the heterogeneous photolysis of HNO on PM was identified as the most substantial source of HONO (contributing 52.5 %). This study highlights the significant variations in primary HONO sources throughout the day.
亚硝酸（HONO）是一种公认的羟基（OH）自由基前体，对颗粒物（PM）和臭氧（O₃）的形成有重大影响。尽管近年来对HONO观测进行了广泛研究，但关于其在城市地区的来源和汇的认识仍然不足。在本研究中，我们在中国西南部大城市成都市区的一个超级站点，于春季同时监测了HONO及相关污染物（包括气态硝酸和颗粒态硝酸盐）的大气浓度，选择春季是因为该季节对PM和O₃污染都具有耐受性。此外，我们采用随机森林模型来填补HONO的缺失数据，该模型表现出良好的预测性能（R = 0.96，均方根误差RMSE = 0.36 ppbv）。在此次监测期间，测得HONO的平均混合比为1.0 ± 0.7 ppbv。值得注意的是，在O₃和PM浓度较高的时期，HONO的混合比相比清洁时期高出50%以上。我们制定了一个全面的HONO收支参数化方案，该方案在模拟HONO的日变化方面表现良好。基于HONO收支分析，我们确定了在一天中不同时间主导HONO形成的不同机制。发现车辆排放和NO非均相转化是夜间（从18:00至次日7:00）HONO的主要来源（分别占21.0%、30.2%）。在早晨（7:00 - 12:00），NO非均相转化和NO与OH的反应成为主要来源（分别占35.0%、32.2%）。然而，在下午（12:00 - 18:00），HNO₃在颗粒物上的非均相光解被确定为HONO的最主要来源（贡献52.5%）。本研究突出了一天中HONO主要来源的显著变化。
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