Contribution of Atmospheric Oxygenated Organic Compounds to Particle Growth in an Urban Environment

Abstract

Gas-phase oxygenated organic molecules (OOMs) can contribute substantially to the growth of newly formed particles. However, the characteristics of OOMs and their contributions to particle growth rate are not well understood in urban area, which has complex anthropogenic emissions and atmospheric conditions. We performed long-term measurement of gas-phase OOMs in urban Beijing during 2018-2019 using nitrate-based chemical ionization mass spectrometry. OOM concentrations showed clear seasonal variations, with the highest in summer and the lowest in winter. Correspondingly, calculated particle growth rates due to OOM condensation were highest in summer, followed by spring, autumn, and winter. One prominent feature of OOMs in this urban environment was a high fraction (~75%) of nitrogen-containing OOMs. These nitrogen-containing OOMs contributed only 50%-60% of the total growth rate led by OOM condensation, owing to their slightly higher volatility than non-nitrate OOMs. By comparing the calculated condensation growth rates and the observed particle growth rates, we showed that sulfuric acid and its clusters are the main contributors to the growth of sub-3 nm particles, with OOMs significantly promoting the growth of 3-25 nm particles. In winter Beijing, there are missing contributors to the growth of particles above 3 nm, which remain to be further investigated.

The effect of COVID-19 restrictions on atmospheric new particle formation in Beijing

“…However, the reduction of PM2.5 was considerably weaker than those of the primary pollutants, and in some cities such as Beijing, the PM2.5 concentrations even increased after the lockdown policy was imposed (Huang et al, 2021). This persistent particulate pollution has been attributed to both unfavorable meteorology, such as stagnant meteorological conditions and high relative humidity (RH) (Le et al, 2020;Wang et al, 2020b) and to enhanced atmospheric oxidative capacity caused by increased O3 and NO3 radical formation (Huang et al, 2021;Le et al, 2020). To date, few studies have focused on either atmospheric new particle formation or the overall particle number size distribution (Shen et al, 2021a;Shen et al, 2021b) during the lockdown period, although NPF has been shown to enhance haze formation (Guo et al, 2014;, and the particle number size distribution is known to influence the health effect of particles (Harrison et al, 2010).…”

“…The reductions of primary emissions mitigated particulate pollution and improved air quality in many countries around the globe (Sicard et al, 2020;Krecl et al, 2020;Agarwal et al, 2020;Ciarelli et al, 2021), including many Chinese cities (Wang et al, 2020b;Huang et al, 2021;Le et al, 2020). However, the reduction of PM2.5 was considerably weaker than those of the primary pollutants, and in some cities such as Beijing, the PM2.5 concentrations even increased after the lockdown policy was imposed (Huang et al, 2021).…”

“…The reductions of primary emissions mitigated particulate pollution and improved air quality in many countries around the globe (Sicard et al, 2020;Krecl et al, 2020;Agarwal et al, 2020;Ciarelli et al, 2021), including many Chinese cities (Wang et al, 2020b;Huang et al, 2021;Le et al, 2020). However, the reduction of PM2.5 was considerably weaker than those of the primary pollutants, and in some cities such as Beijing, the PM2.5 concentrations even increased after the lockdown policy was imposed (Huang et al, 2021). This persistent particulate pollution has been attributed to both unfavorable meteorology, such as stagnant meteorological conditions and high relative humidity (RH) (Le et al, 2020;Wang et al, 2020b) and to enhanced atmospheric oxidative capacity caused by increased O3 and NO3 radical formation (Huang et al, 2021;Le et al, 2020).…”

“…The contrast between the enhanced NPF and reduced traffic load during the lockdown period seems to support the former mechanism, but a detailed investigation of how molecular clustering responded to those emission reductions remains lacking. For the growth phase, oxygenated organic molecules (OOMs) have been shown to dominate in some cases Qiao et al, 2021). Further, a high fraction of nitrogen containing OOMs suggests that RO2+NOx reactions prevail in OOM formation (Qiao et al, 2021).…”

“…For the growth phase, oxygenated organic molecules (OOMs) have been shown to dominate in some cases Qiao et al, 2021). Further, a high fraction of nitrogen containing OOMs suggests that RO2+NOx reactions prevail in OOM formation (Qiao et al, 2021). For monoterpene-derived OOMs, which is characteristic of a remote atmosphere, high NOx levels can suppress particle growth by altering a fraction of products to organic nitrates with higher volatilities .…”