A suite of instruments was deployed to simultaneously measure nitrous acid (HONO), nitrogen oxides (NOx = NO + NO2), carbon monoxide (CO), ozone (O3), volatile organic compounds (VOCs – including formaldehyde, HCHO) and meteorological parameters near a typical industrial zone in Nanjing in the Yangtze River Delta (YRD) region of China from 1 to 31?December?2015. High levels of HONO were detected using a wet-chemistry-based method. HONO ranged from 0.03 to 7.04ppbv with an average of 1.32±0.92ppbv. Elevated daytime HONO was frequently observed with a minimum of several hundred parts per trillion by volume (pptv) on average, which cannot be explained by the homogeneous OH + NO reaction (POH+NO) and primary emissions (Pemission), especially during periods with high particulate matter (PM2.5) loadings. HONO chemistry and its impact on the atmospheric oxidation capacity in the study area were further investigated using a Master Chemical Mechanism (MCM) box model. The results show that the average hydroxyl radical (OH) production rate was dominated by the photolysis of HONO (7.13×106molec.cm?3s?1), followed by the ozonolysis of alkenes (3.94×106molec.cm?3s?1), the photolysis of O3 (2.46×106molec.cm?3s?1) and the photolysis of HCHO (1.60×106molec.cm?3s?1) during the campaign period, especially within plumes that originated from the industrial zone. Model simulations indicated that heterogeneous chemistry played an important role in HONO formation. The average nighttime NO2 to HONO conversion rate was determined to be ～0.8%h?1. A good correlation between nocturnal HONO∕NO2 and the product of particle surface area density (S∕V) and relative humidity (RH), S/V?RH, supports the heterogeneous NO2∕H2O reaction mechanism. The other HONO source, designated as Punknonwn, was about twice as high as POH+NO on average and displayed a diurnal profile with an evidently photo-enhanced feature, i.e., photosensitized reactions of NO2 may be an important daytime HONO source. Nevertheless, our results suggest that daytime HONO formation was mostly due to the light-induced conversion of NO2 on aerosol surfaces, whereas heterogeneous NO2 reactions on the ground surface dominated nocturnal HONO production. Our study indicated that an elevated PM2.5 level during haze events can promote the conversion of NO2 to HONO by providing more heterogeneous reaction sites, thereby increasing the atmospheric oxidation capacity, which may further promote the formation of secondary air pollutants. Highlights: High levels of HONO, with an average of 1.32±0.92ppbv, were observed near one of the largest industrial zones in the YRD region of China. HONO photolysis and alkene ozonolyses contributed the most to OH production and, hence, the atmospheric oxidation capacity. High loading of PM2.5 provided additional reaction surfaces for HONO formation. Heterogeneous formation mechanisms were the most important daytime HONO sources and were further enhanced by sunlight.
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机译：器械的套件被部署到同时测量亚硝酸（HONO），氮氧化物（NOx = NO + NO 2），一氧化碳（CO），臭氧（O3），挥发性有机化合物（VOC - 包括甲醛，HCHO）和气象参数在附近的南京从1到31？月？2015年一个典型的工业区在中国的长江三角洲（长三角）地区。使用基于湿化学法检测HONO的高水平。 HONO范围从0.03至7.04ppbv平均1.32±0.92ppbv的。升高的白天HONO频繁与由体积（PPTV）平均最小的每万亿几百份，它不能被均匀OH + NO反应（POH + NO）和初级排放（Pemission），尤其是在与周期地解释观察到的高颗粒物（PM2.5）的负载。亚硝酸化学及其对研究区大气氧化能力影响使用主化学机制（MCM）盒模型进行了进一步调查。结果表明，平均羟基自由基（OH）生产速率通过HONO的光解支配（7.13×106molec.cm？3S？1），其次是烯烃的臭氧分解（3.94×106molec.cm？3S？1）， O3的光解（2.46×106molec.cm？3S？1）和HCHO的光解（1.60×106molec.cm？3S？1）在活动期间，尤其是在源自工业区羽流。模型模拟表明，多相化学起到了亚硝酸形成的重要作用。平均夜间NO2到HONO转化率经测定为〜0.8％H 2 1。夜间HONO / NO 2和颗粒表面积密度（S / V）和相对湿度（RH）的产物之间的良好的相关性，S / V？RH，支持异构NO2 / H 2 O反应机理。其他HONO源，指定为Punknonwn，正要两倍高平均POH + NO和具有明显光增强特征，即，NO 2的光敏反应可能是一个重要的白天HONO源显示的昼夜曲线。然而，我们的研究结果表明，白天HONO形成主要是由于NO 2的气溶胶表面上的光诱导转化，而在地面上异质NO2反应为主的夜间HONO生产。我们的研究表明，在雾度事件的升高PM2.5低电平可以通过提供更多的异构反应位点，从而增加了大气氧化能力，这可以进一步促进二次空气污染物的形成促进NO2到HONO的转化。亮点：高浓度HONO的，平均为1.32±0.92ppbv，靠近中国的长三角地区最大的工业区之一，观察。 HONO光解和烯烃ozonolyses贡献最大的OH生产，因此，大气氧化能力。 PM2.5的高负载为HONO形成提供另外的反应表面。异质形成机制是最重要的白天HONO源和由阳光被进一步增强。
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