EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Heterogeneous formation of HONO and its impacts on haze formation in the YRD region of China

Jun Zheng, Xiaowen Shi, and Yan Ma
Jun Zheng et al.
  • Nanjing University of Information Science & Technology, Nanjing, China (

A suite of instruments were 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 of the Yangtze River Delta region, China. High levels of HONO were detected using a wet chemistry-based method. HONO ranged from 0.03-7.04 ppbv with an average of 1.32 ±0.92 ppbv. Elevated daytime HONO was frequently observed with a minimum of several hundreds of pptv on average, which cannot be explained by the homogeneous OH + NO reaction (POH+NO) alone, especially during periods with high loadings of particulate matters (PM2.5). The HONO chemistry and its impact on atmospheric oxidation capacity in the study area were further investigated using a MCM-box model. The results show that the average hydroxyl radical (OH) production rate was dominated by the photolysis of HONO (7.13×106molecules cm-3 s-1), followed by ozonolysis of alkenes (3.94×106molecules cm-3 s-1), photolysis of O3(2.46×106molecules cm-3 s-1) and photolysis of HCHO (1.60×106molecules cm-3 s-1), especially within the plumes originated from the industrial zone. The observed similarity between HONO/NO2and HONO in diurnal profiles strongly suggests that HONO in the study area was likely originated from NO2heterogeneous reactions. The averagenighttimeNO2to HONO conversion ratewas determined to be ~0.9% hr-1. Good correlation between nocturnal HONO/NO2and the products 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 much as POH+NO on average and displayed a diurnal profile with an evidently photo-enhanced feature, i.e., photosensitized reactions of NO2may be an important daytime HONO source. Nevertheless, our results suggest that daytime HONO formation was mostly due to the light-induced conversion of NO2on aerosol surfaces but heterogeneous NO2reactions on ground surface dominated nocturnal HONO production. Concurred elevated HONO and PM2.5levels strongly indicate that high HONO may increase the atmospheric oxidation capacity and further promote the formation of secondary aerosols, which may in turn synergistically boost NO2/HONO conversion by providing more heterogeneous reaction sites.

How to cite: Zheng, J., Shi, X., and Ma, Y.: Heterogeneous formation of HONO and its impacts on haze formation in the YRD region of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3202,, 2020