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

Abstract

<p><strong>Abstract.</strong> 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 NO<sub>x</sub> were derived from 55 fresh plumes (NO / NO<sub>x</sub> > 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 NO<sub>x</sub> indicate that NO<sub>x</sub> is the critical precursor of HONO. During the nighttime, the chemistry of HONO was found to depend on RH, and heterogeneous reaction of NO<sub>2</sub> on aerosol surface was presumably responsible for HONO production. The average nighttime NO<sub>2</sub>-to-HONO conversion frequency (CHONO) was determined to be 0.0055 ± 0.0032 h<sup>−1</sup> 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<sup>−1</sup>, 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.</p>

Atmospheric nitrous acid (HONO) at a rural coastal site in North China: Seasonal variations and effects of biomass burning

“…C HONO presented a strong correlation with ambient temperature (r ¼ 0.76) and a moderate relationship with RH (r ¼ 0.57), which was consistent with the study of Wen et al (2019) in a marine boundary layer. The average C HONO at our site was within the range of 0.43-3.36% h À 1 that determined from other studies around the world (Liu et al, 2019;Xu et al, 2015). Seasonal variation of C HONO has also been found by Liu et al (2019) at a suburban site in Nanjing in the subtropical zone with four distinct seasons.…”

“…The average C HONO at our site was within the range of 0.43-3.36% h À 1 that determined from other studies around the world (Liu et al, 2019;Xu et al, 2015). Seasonal variation of C HONO has also been found by Liu et al (2019) at a suburban site in Nanjing in the subtropical zone with four distinct seasons.…”

“…To investigate the strength of the daytime HONO sources and their seasonal variations, we performed a budget analysis based on the description by equation (E3) (Liu et al, 2019;Su et al, 2008b). The HONO sources include direct emission from anthropogenic combustions (P emis ), the well-accepted homogeneous formation from reaction R3 (P OHþNO ), and the remaining other sources (P other ).…”

The role of HONO in O<sub>3</sub> formation and insight into its formation mechanism during the KORUS-AQ Campaign

“…However, the conversion ratio decreased when RH was over 80 %, like the HONO concentration. This phenomenon already reported, and Wojtal et al, suggested that it was caused by the surface loss or particle loss in marine boundary layers, which is in accordance with what we found in the present study discussed in section 3.1 (Liu et al, 2019b;Wojtal et al, 2011).Therefore, the observed HONO is likely to be formed through heterogeneous conversion which is mainly controlled by factors like NOx, RH, and surface area.…”

The promotion effect of nitrous acid on aerosol formation in wintertime Beijing: possible contribution of traffic-related emission

“…2A). Owing to the high HONO concentration accumulated throughout the night, the maximal POH-HONO in winter was as about 2-6 times of that was observed in the wintertime of Colorado, USA (~0.59 ppb h -1 ) (Kim et al, 2014), New York, USA (~0.40 ppb h -1 ) (Kanaya et al, 2007) and Nanjing, China (0.900.27 ppb h -1 ) (Liu et al, 2019b). In the period from April to June, the daily maxima of POH-HONO and POH-O3 were 2.481.42 × 10 7 molecules cm -3 s -1 (3.481.99 ppb h -1 ) and 6.514.17 × 10 7 molecules cm -3 s -1 (9.155.86 ppb h -1 ), respectively.…”