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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Apr 2019

Submitted as: research article | 25 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Contributions of different sources to nitrous acid (HONO) at the SORPES station in eastern China: results from one-year continuous observation

Yuliang Liu1,2, Wei Nie1,2, Zheng Xu1,2, Tianyi Wang1,2, Ruoxian Wang1,2, Yuanyuan Li1,2, Lei Wang1,2, Xuguang Chi1,2, and Aijun Ding1,2 Yuliang Liu et al.
  • 1Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing, Jiangsu Province, China
  • 2Collaborative Innovation Center of Climate Change, Jiangsu Province, China

Abstract. Nitrous acid (HONO), a reservoir of the hydroxyl radical (OH), has been long-standing recognized to be of significant importance to atmospheric chemistry, but its sources are still debate. In this study, we conducted continuous measurement of HONO from November 2017 to November 2018 at SORPES station in Nanjing of eastern China. The yearly average mixing ratio of observed HONO was 0.69 ± 0.58 ppb, showing a larger contribution to OH relative to ozone with a mean OH production rate of 0.90 ± 0.27 ppb/h. To estimate the effect of combustion emissions of HONO, the emitted ratios of HONO and NOx were derived from 55 fresh plumes (NO / NOx > 0.85), with a mean value of 0.79 %. The well-defined seasonal and diurnal patterns with clear wintertime and early morning concentration peaks of both HONO and NOx indicate that NOx is the critical precursor of HONO. During the nighttime, the chemistry of HONO was found to depend on RH, and heterogeneous reaction of NO2 on aerosol surface was presumably responsible for HONO production. The average nighttime NO2-to-HONO conversion frequency (CHONO) was determined to be 0.0055 ± 0.0032 h−1 from 137 HONO formation cases. The missing source of HONO around noontime seemed to be photo-induced with an average Punknown of 1.13 ± 0.95 ppb h−1, based on a semiquantitative HONO budget analysis. An over-determined system of equations was applied to obtain the monthly variations in nocturnal HONO sources. Except for burning-emitted HONO (approximately 23 % of total measured HONO), the contribution of heterogeneous formation on ground surfaces was an approximately constant proportion of 36 % throughout the year. The soil emission revealed clear seasonal variation, and contributed up to 40 % of observed HONO in July and August. A higher propensity for generating HONO on aerosol surface occurred in heavily polluted period (about 40 % of HONO in January). Our results highlight ever-changing contributions of HONO sources, and encourage more long-term observations to evaluate the contribution from varied sources.

Yuliang Liu et al.
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Yuliang Liu et al.
Yuliang Liu et al.
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Short summary
We conducted one-year continuous measurement of HONO at SORPES station. We obtained seasonal and diurnal variations of HONO, and evaluated the contribution of HONO photolysis to OH radical and the missing daytime source of HONO. We separated the sources of nocturnal HONO into four parts: combustion emissions, soil emission, formation on ground and formation on aerosol, and estimate their contribution semi-quantitatively. The results highlighted ever-changing contributions of HONO sources.
We conducted one-year continuous measurement of HONO at SORPES station. We obtained seasonal and...