Remarkable nucleation and growth of ultrafine particles from vehicular exhaust

Abstract

High levels of ultrafine particles (UFPs; diameter of less than 50 nm) are frequently produced from new particle formation under urban conditions, with profound implications on human health, weather, and climate. However, the fundamental mechanisms of new particle formation remain elusive, and few experimental studies have realistically replicated the relevant atmospheric conditions. Previous experimental studies simulated oxidation of one compound or a mixture of a few compounds, and extrapolation of the laboratory results to chemically complex air was uncertain. Here, we show striking formation of UFPs in urban air from combining ambient and chamber measurements. By capturing the ambient conditions (i.e., temperature, relative humidity, sunlight, and the types and abundances of chemical species), we elucidate the roles of existing particles, photochemistry, and synergy of multipollutants in new particle formation. Aerosol nucleation in urban air is limited by existing particles but negligibly by nitrogen oxides. Photooxidation of vehicular exhaust yields abundant precursors, and organics, rather than sulfuric acid or base species, dominate formation of UFPs under urban conditions. Recognition of this source of UFPs is essential to assessing their impacts and developing mitigation policies. Our results imply that reduction of primary particles or removal of existing particles without simultaneously limiting organics from automobile emissions is ineffective and can even exacerbate this problem. new particle formation | nucleation | ultrafine particles | growth | organics

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

“…On the other hand, the correlation between Csulfate/CCO and -CHONO/CCO was much weaker (R=0.26), suggesting a weak connection between particle-phase sulfate and gas-phase H2SO4. This was also consistent with the previous understanding that heterogeneous reactions of SO2 were the dominating pathway for sulfate formation (Zheng et al, 2015a;He et al, 2018;Zhang et al, 2020). Overall, this work well supported the recent modeling results that HONO could obviously promote the aerosol production in winter (Zhang et al, 2019a;Zhang et al, 2019b;Xing et al, 2019;An et al, 2013) from the point of view of observation.…”

“…It was around 2 times compared to places such as Tokyo (Kanaya et al, 2007) and New York City (Ren et al, 2006). A very recent work has found that oxidation of VOCs from local traffic emission is still efficient even under pollution conditions (Guo et al, 2020). This implies that oxidation of atmospheric trace gases by OH may still be highly effective even in wintertime, thereby facilitating the vigorous formation of secondary pollutants in…”

“…Vehicle population in China is increasing very quickly (Liu et al, 2017b;Wang et al, 2011). Thus, the negative influences of the vehicle emission on air quality will increase especially in populous metropolitan areas (Yang et al, 2019;Guo et al, 2020), such as Beijing and Shanghai, if targeted pollution control technologies are not applied.…”

“…Secondary aerosol can contribute up to ~70 % to the aerosol mass concentration in polluted days (Huang et al, 2014). Several reaction pathways have been proposed in the atmospheric chemistry community, such as sulfate formation via heterogeneous oxidation of SO2 promoted by H2O2 and/or NO2 on mineral dust (Huang et al, 2015;He et al, 2014), aqueous oxidation of SO2 promoted by NO2 in the presence or absence of NH3 in particle-bound water film (He et al, 2014;Wang et al, 2016), catalytic conversion of SO2 to sulfate by black carbon (Zhang et al, 2020), nitrate formation via efficient hydrolysis of N2O5 on aerosol surfaces (Wang et al, 2017c;Kulmala, 2018;Li et al, 2017), and the haze formation initiated by new particle https://doi.org/10.5194/acp-2020-150 Preprint. Discussion started: 21 February 2020 c Author(s) 2020.…”

“…formation and growth (Guo et al, 2014;Guo et al, 2020). During the past years, strict control of coal combustion has successfully reduced the SO2 concentration, resulting in a reduction of sulfate (SO4 2-) component in PM2.5; in stark contrast, the contributions from organic and nitrate become increasingly more significant in China (Lang et al, 2017).…”