Influences of Atmospheric Pollution on the Contributions of Major Oxidation Pathways to PM_2.5 Nitrate Formation in Beijing

Abstract

Nitrate (NO3−), which is mainly oxidized from NO2 by the OH radical (OH·) and O3 in the atmosphere, is a major component of inorganic aerosols. However, the contributions of the OH· and O3 pathways to NO3− in urban aerosols and the influence of air pollution to both pathways remain unclear. Oxygen isotopes of NO3− were measured for PM2.5 in Beijing in 2014. The Δ17O‐NO3− values (17.0–32.8‰) were significantly higher in winter (27.2 ± 3.6‰) than in summer (24.2 ± 1.3‰). By estimating contributions of O3 to the NOx cycle, the Δ17O values of NO3− endmembers produced via the NO2 + OH· (P1), NO3· + DMS/HC (P2), and N2O5 hydrolysis (P3) pathways were calculated for each observation. The contributions of the three pathways (P1: 32 ± 10%, P2: 34 ± 10%, and P3: 34 ± 20% annually) were calculated using the Stable Isotope Analysis in R model. We found that NO3− formation was dominated by the O3 oxidation pathways (P2 + P3; 68 ± 23% annually, 73 ± 21% in spring, 59 ± 23% in summer, 75 ± 20% in autumn, and 69 ± 22% in winter). Moreover, PM2.5, NO2, and NO3− pollution decreased the importance of the OH· pathway relative to the O3 pathways for NO3− production. However, O3 pollution increased the importance of the OH· pathway relative to the O3 pathways for NO3− production. These results provided a comprehensive analysis on the oxygen isotope records in particulate NO3− for understanding the relative importance of major oxidation pathways of NO2. Atmospheric pollution substantially influenced the pathways of NO2 oxidation to NO3− in city environments.

Differentiation Between Nitrate Aerosol Formation Pathways in a Southeast Chinese City by Dual Isotope and Modeling Studies

“…And then we can calculate the source apportionment (Zong et al, 2017 Previous studies suggested that the oxidation pathway of NO 3 + HC/DMS (DMS is a major in coastal environments) to form HNO 3 (3) is also very important (Alexander et al, 2009;He et al, 2018;Walters & Michalski, 2016;Wang et al, 2019). However, few studies have quantitatively calculated its contribution (Alexander et al, 2009(Alexander et al, , 2020Wang et al, 2019). In our second model, we used a δ 15 N and δ 18 O array of NO 3 − in PM 2.5 to determine the contributions of all three major oxidation pathways using the MixSIAR model.…”

“…Atmospheric reactive nitrogen (e.g., gaseous nitrogen oxides and ammonia and anion nitrate) causes serious environmental problems worldwide (Duce et al, 2008;Galloway et al, 2004;He et al, 2018;Xiao et al, 2015). Nitrate (NO 3 − ) is an important component of PM 2.5 (aerodynamic diameters <2.5 μm) in many Chinese urban atmospheres (Guo et al, 2020;Huang et al, 2014;Luo et al, 2019;Wang et al, 2019). As a precursor of NO 3 − , NO x (NO and NO 2 ) is a major component of reactive nitrogen in the atmosphere, mainly derived from anthropogenic activities, such as combustion of fossil fuels (Alexander et al, 2009(Alexander et al, , 2020Galloway et al, 2008;Xiao et al, 2015).…”

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

“…Several reaction pathways have been proposed, such as sulfate formation via the heterogeneous oxidation of SO 2 promoted by H 2 O 2 and/or NO 2 on mineral dust (Huang et al, 2015;He et al, 2014), the aqueous oxidation of SO 2 promoted by NO 2 in the presence or absence of NH 3 in the particle-bound water film (He et al, 2014;Wang et al, 2016), the catalytic conversion of SO 2 to sulfate by black carbon (Zhang et al, 2020), nitrate formation via the efficient hydrolysis of N 2 O 5 on aerosol surfaces (Z. Wang et al, 2019;Kulmala, 2018;, and haze formation initiated by new particle formation and growth (Guo et al, 2014(Guo et al, , 2020. In recent years, the strict control of coal combustion has successfully reduced the SO 2 concentration, resulting in a reduction of the sulfate (SO 2− 4 ) component of the PM 2.5 .…”

Chemical Characteristics of Major Inorganic Ions in PM2.5 Based on Year-Long Observations in Guiyang, Southwest China—Implications for Formation Pathways and the Influences of Regional Transport

“…As •OH production decreases on hazy days, the oxidization of NO 2 via the O 3 pathway might increase with increasing NO 2 emissions; this could result in a higher NOR and would have a positive impact on the concentration of PM2.5 [55]. Thus, in our study, NO 3 − formation may be dominated by the O 3 oxidation pathway during hazy days [53]. On the other hand, as discussed above, there were inverse relationships between temperature and both the NO 3 − and PM2.5 concentrations and more NO 2 was oxidized to NO 3 − in winter resulting in an increased PM2.5 concentration.…”

“…Furthermore, the NOR was highest in winter (>0.1), which indicates that more NO 2 was oxidized to NO 3 − . The Meng et al [48] has reported that the heterogeneous reactions main occur in winter and the availability of HO• for NO 2 oxidization become lower with increasing NO 2 concentrations [53]. Meanwhile, relatively higher proportions of NO 2 would be oxidized by the O 3 , even though the O 3 concentrations were lower in winter.…”