Atmospheric measurements at Mt. Tai – Part I: HONO formation and its role in the oxidizing capacity of the upper boundary layer

Abstract

Abstract. A comprehensive field campaign, with measurements of HONO and related parameters, was conducted in summer 2018 at the foot (150 m a.s.l.) and the summit (1534 m a.s.l.) of Mt. Tai (Shandong province, China). At the summit station, high HONO mixing ratios were observed (mean ± 1σ: 133 ± 106 pptv, maximum: 880 pptv), with a diurnal noontime peak (mean ± 1σ: 133 ± 72 pptv at 12:30 local time). Constraints on the kinetics of aerosol-derived HONO sources (NO2 uptake on the aerosol surface and particulate nitrate photolysis) were performed and discussed, which enables a better understanding of the interaction of HONO and aerosols, especially in the polluted North China Plain. Various evidence of air mass transport from the ground to the summit level was provided. Furthermore, daytime HONO formation from different paths and its role in radical production were quantified and discussed. We found that the homogeneous reaction NO + OH could only explain 8.0 % of the daytime HONO formation, resulting in strong unknown sources (Pun). Campaigned-averaged Pun was about 290 ± 280 pptv h−1, with a maximum of about 1800 pptv h−1. Aerosol-derived HONO formation mechanisms were not the major sources of Pun at the summit station. Their contributions to daytime HONO formation varied from negligible to moderate (similar to NO + OH), depending on the chemical kinetic parameters used. Coupled with sensitivity tests on the kinetic parameters used, the NO2 uptake on the aerosol surface and particulate nitrate photolysis contributed 1.5 %–19 % and 0.6 %–9.6 % of the observed Pun, respectively. Based on synchronous measurements at the foot and the summit station, an amount of field evidence was proposed to support the finding that the remaining majority (70 %–98 %) of Pun was dominated by the rapid vertical transport from the ground to the summit level and heterogeneous formation on the mountain surfaces during transport. HONO photolysis at the summit level initialized daytime photochemistry and still represented an essential OH source in the daytime, with a contribution of about one-quarter of O3. We provided evidence that ground-derived HONO played a significant role in the oxidizing capacity of the upper boundary layer through the enhanced vertical air mass exchange driven by mountain winds. The follow-up impacts should be considered in regional chemistry transport models.

Unveiling the underestimated direct emissions of nitrous acid (HONO)

“…3 D ). The contribution of overall direct HONO emissions (39 ~ 45%) in the three seasons was remarkably higher than previous studies that considered only combustion-related emissions (10 ~ 28%) ( 15 , 119 , 120 ), highlighting the significance of direct HONO emissions, particularly from the livestock sector. Remarkably, the seasonal variation of contributions from direct emission sources at the Wangdu site is consistent with the isotopic changes of atmospheric HONO at the rural site in the Jiaodong, east of the NCP ( Fig.…”

Soil Emissions of Reactive Nitrogen Accelerate Summertime Surface Ozone Increases in the North China Plain

“…Figure presents the N r emissions from anthropogenic fuel combustion and soil emissions in June–July. We note that we do not include traffic HONO emissions due to the lack of available emission inventory, and also because the traffic HONO emissions are much smaller than those from soil and contribute negligibly to the daytime HONO except for central urban areas. ,, For June–July 2019, the anthropogenic fuel combustion NO x emissions, soil NO x emissions, and soil HONO emissions over China are 1.12, 0.24, and 0.15 Tg N, respectively. Specifically for the NCP region, the corresponding emissions are 0.21, 0.08, and 0.04 Tg N. We find that the soil N r emissions account for 24% of total (soil plus fuel combustion) N r emissions in the NCP in 2013, but this ratio substantially increases since 2013 to an exceptionally high value of 35% in 2019, with the rapid decrease in combustion sources and increase in soil NO x emission driven by increasing soil temperature (Figure S7).…”

Nitrous Acid Budgets in Coastal Atmosphere: Insights into the Absence of a Daytime Marine Source

“…Prior research indicates that direct emissions contribute significantly to HONO concentration in urban settings (Zhang et al, 2019;Kramer et al, 2020). However, in rural and background areas, the vehicular contribution is comparatively insignificant (Liu et al, 2019b;Xue et al, 2022). Consequently, the contribution of vehicle emissions to HONO is not constant and varies based on the environment and traffic density.…”

“…(c) Heterogeneous reactions of NO2 on various surfaces, such as mineral dust (Underwood et al, 2001), soil (Kebede et al, 2016), and aqueous surfaces (Wojtal et al, 2011). The uptake coefficient of NO2, γ(NO2), on these surfaces remains uncertain and is subject to varying factors, sparking debates regarding the importance of the heterogeneous conversion of NO2 (Xue et al, 2022;Broske et al, 2003). (d) Photolysis of adsorbed nitric acid (HNO3) and particulate nitrate (pNO3 -), crucial contributors to daytime HONO formation (Gen et al, 2022;Ye et al, 2017), particularly in clean environments (Zhou et al, 2011;Ye et al, 2016a).…”

“…Conversely, in remote areas, nitrate photolysis or soil emissions are perceived as significant contributors to daytime HONO sources (Cui et al, 2019;Ye et al, 2016a;Su et al, 2011). In polluted mountainous areas, the vertical transport of air masses may also contribute to observed daytime HONO concentrations (Jiang et al, 2020;Xue et al, 2022). During dust storms, the particle surface area increases sharply, potentially enhancing the heterogeneous reaction of NO2, yet the evaluations of dust impacts on daytime HONO are scarce (Wang, 2003).…”