Budget of nitrous acid (HONO) at an urban site in the fall season of Guangzhou, China

Abstract

Abstract. High concentrations of nitrous acid (HONO) have been observed in the Pearl River Delta (PRD) region of China in recent years, contributing to an elevated atmospheric oxidation capacity due to the production of OH through HONO photolysis. We investigated the budget of HONO at an urban site in Guangzhou from 27 September to 9 November 2018 using data from a comprehensive atmospheric observation campaign. During this period, measured concentrations of HONO were 0.02 to 4.43 ppbv, with an average of 0.74 ± 0.70 ppbv. An emission ratio (HONO/NOx) of 0.9 ± 0.4 % was derived from 11 fresh plumes. The primary emission rate of HONO at night was calculated to be between 0.04 ± 0.02 and 0.30 ± 0.15 ppbv h−1 based on a high-resolution NOx emission inventory. Heterogeneous conversion of NO2 on the ground surface (0.27 ± 0.13 ppbv h−1), primary emissions from vehicle exhaust (between 0.04 ± 0.02 and 0.30 ± 0.15 ppbv h−1, with a middle value of 0.16 ± 0.07 ppbv h−1), and the homogeneous reaction of NO + OH (0.14 ± 0.30 ppbv h−1) were found to be the three largest sources of HONO at night. Heterogeneous NO2 conversion on aerosol surfaces (0.03 ± 0.02 ppbv h−1) and soil emission (0.019 ± 0.009 ppbv h−1) were two other minor sources. Correlation analysis shows that NH3 and the relative humidity (RH) may have participated in the heterogeneous transformation of NO2 to HONO at night. Dry deposition (0.41 ± 0.31 ppbv h−1) was the main removal process of HONO at night, followed by dilution (0.18 ± 0.16 ppbv h−1), while HONO loss at aerosol surfaces was much slower (0.008 ± 0.006 ppbv h−1). In the daytime, the average primary emission Pemis was 0.12 ± 0.02 ppbv h−1, and the homogeneous reaction POH+NO was 0.79 ± 0.61 ppbv h−1, larger than the unknown source PUnknown (0.65 ± 0.46 ppbv h−1). Similar to previous studies, PUnknown appeared to be related to the photo-enhanced conversion of NO2. Our results show that primary emissions and the reaction of NO + OH can significantly affect HONO at a site with intensive emissions during both the daytime and nighttime. Uncertainty in parameter values assumed in the calculation of HONO sources can have a strong impact on the relative importance of HONO sources at night, and could be reduced by improving knowledge of key parameters such as the NO2 uptake coefficient. The uncertainty in the estimated direct emission can be reduced by using emission data with higher resolution and quality. Our study highlights the importance of better constraining both conventional and novel HONO sources by reducing uncertainties in their key parameters for advancing our knowledge of this important source of atmospheric OH.

Insights into characteristics and formation mechanisms of secondary organic aerosols in Guangzhou urban area

“…CC BY 4.0 License. variations of oxidation levels and other sources such as HONO photolysis (Yu et al, 2022) also 384 contribute to OH radicals and is a typical oxidant in daytime photochemistry. To investigate the 385 possible roles of aqueous reactions in SOA formation, the relationship between apparent SOA rates 386 and corresponding average ALWC were also investigated, and a positive but weak correlation was 387 found (r=0.33).…”

Observationally Constrained Modeling of Peroxy Radical During an Ozone Episode in the Pearl River Delta Region, China

“…Based on the differences in the types of inorganic compounds, organic compounds (further dividing OVOCs into dialdehydes and nondialdehydes) and radicals, 15 sensitivity tests (Table 3) were designed and performed with the box model to identify the changes in RO 2 * concentrations resulting from constraining and not constraining HONO, OVOC species and NO 3 radicals. The HONO data were measured at the same site with a custom‐built long‐path absorption photometer (Yu et al., 2022).…”

Pyrogenic HONO seen from space: insights from global IASI observations

“…Note that the method described here is specifically designed for the detection of pyrogenic HONO. Although elevated HONO concentrations are associated with anthropogenic activities (Spataro and Ianniello, 2014;VandenBoer et al, 2014;Kramer et al, 2020;Zheng et al, 2020;Yu et al, 2022;Zhang et al, 2023a), up to now no HRI enhancements have been observed with IASI in proximity to anthropogenic sources (e.g., megacities, industrial clusters).…”

“…While routine in situ measurements at the (near) surface provide valuable insights on HONO, particularly in polluted regions (VandenBoer et al, 2014;Kramer et al, 2020;Zheng et al, 2020;Yu et al, 2022;Zhang et al, 2023a), the atmospheric distribution of HONO is still poorly represented, especially in the free troposphere (Spataro and Ianniello, 2014), notably due to its high reactivity. For instance, HONO observations in biomass burning events were usually limited to local measurements from aircraft and ground-based campaigns (Yokelson et al, 2009;Roberts et al, 2010;Neuman et al, 2016;Peng et al, 2020Peng et al, , 2022Bourgeois et al, 2022).…”