Photochemical smog in China: scientific challenges and implications for air-quality policies

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Abstract. Severe wintertime haze events with exceedingly high levels of aerosols have occurred frequently in China in recent years, impacting human health, weather, and the climate. A better knowledge of the formation mechanism and aerosol properties during haze events is helpful for the development of effective mitigation policies. In this study, we present field measurements of aerosol properties at an urban site in Beijing during January and February 2015. A suite of aerosol instruments were deployed to measure a comprehensive set of aerosol chemical and physical properties. The evolution of haze events in winter, dependent on meteorological conditions, consistently involves new particle formation during the clean period and subsequently continuous growth from the nucleation mode particles to submicron particles over the course of multiple days. Particulate organic matter is primarily responsible for producing the nucleation mode particles, while secondary organic and inorganic components jointly contribute to the high aerosol mass observed during haze events. The average effective density and hygroscopic parameter (κ) of ambient particles are approximately 1.37 g cm−3 and 0.25 during the clean period and increase to 1.42 g cm−3 and 0.4 during the polluted period, indicating the formation of secondary inorganic species from the continuous growth of nucleation mode particles. Our results corroborate that the periodic cycles of severe haze formation in Beijing during winter are attributed to the efficient nucleation and secondary aerosol growth under high gaseous precursor concentrations and the stagnant air conditions, highlighting that reductions in emissions of aerosol precursor gases are critical for remedying secondary aerosol formation and thereby mitigating haze pollution.

Section: Aerosol Chemical Composition Hygroscopicity and Densitysupporting

confidence: 91%

Wintertime aerosol properties in Beijing

Zamora

Peng

et al. 2019

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“…Within the framework of a Sino-Sweden Joint Research Programme, "Photochemical Smog in China", a summer field campaign was conducted in Beijing to enhance our understanding of secondary chemistry via photochemical smog and heterogeneous reactions (Hallquist et al, 2016). The data presented here were collected at a regional site, PKU-CP (Peking University, Changping campus), from 23 May to 5 June 2016.…”

Section: The Sitementioning

confidence: 99%

“…The reactions of NO 3 + BVOCs are critical to the studies of aerosols on regional and global scales (Fry et al, 2009;Rollins et al, 2009;Pye et al, 2010;Ng et al, 2017). For example, ON had extensive percentages of fine particulate nitrate (pNO − 3 ) (34-44 %) in Europe (Kiendler-Scharr et al, 2016).…”

mentioning

confidence: 99%

Efficient N2O5 uptake and NO3 oxidation in the outflow of urban Beijing

Wang

Guo

et al. 2018

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Abstract. Nocturnal reactive nitrogen compounds play an important role in regional air pollution. Here we present the measurements of dinitrogen pentoxide (N2O5) associated with nitryl chloride (ClNO2) and particulate nitrate (pNO3-) at a suburban site of Beijing in the summer of 2016. High levels of N2O5 and ClNO2 were observed in the outflow of the urban Beijing air masses, with 1 min average maxima of 937 and 2900 pptv, respectively. The N2O5 uptake coefficients, γ, and ClNO2 yield, f, were experimentally determined from the observed parameters. The N2O5 uptake coefficient ranged from 0.012 to 0.055, with an average of 0.034 ± 0.018, which is in the upper range of previous field studies reported in North America and Europe but is a moderate value in the North China Plain (NCP), which reflects efficient N2O5 heterogeneous processes in Beijing. The ClNO2 yield exhibited high variability, with a range of 0.50 to unity and an average of 0.73 ± 0.25. The concentration of the nitrate radical (NO3) was calculated assuming that the thermal equilibrium between NO3 and N2O5 was maintained. In NOx-rich air masses, the oxidation of nocturnal biogenic volatile organic compounds (BVOCs) was dominated by NO3 rather than O3. The production rate of organic nitrate (ON) via NO3 + BVOCs was significant, with an average of 0.10 ± 0.07 ppbv h−1. We highlight the importance of NO3 oxidation of VOCs in the formation of ON and subsequent secondary organic aerosols in summer in Beijing.

“…Many prior chamber experiments revealed the precursors and formation mechanisms of OSs (Surratt et al, 2007(Surratt et al, , 2008(Surratt et al, , 2010Liggio and Li, 2006;Chan et al, 2011;Shalamzari et al, 2014Shalamzari et al, , 2016; however, the atmospheric relevance of these remain unclear. Various biogenic VOC (BVOC) precursors have been reported, including isoprene (Hatch et al, 2011;Surratt et al, 2010), monoterpenes (Surratt et al, 2008), sesquiterpenes (Chan et al, 2011), pinonaldehyde (Liggio and Li, 2006), unsaturated aldehydes (Shalamzari et al, 2014(Shalamzari et al, , 2016, and 2-methyl-3-buten-2-ol . OSs originating from isoprene are some of the most studied compounds and could be among the most abundant OA in some areas (Liao et al, 2015;Chan et al, 2010;Surratt et al, 2010;Lin et al, 2013a;Worton et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

The secondary formation of organosulfates under interactions between biogenic emissions and anthropogenic pollutants in summer in Beijing

Wang

Guo

et al. 2018

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Abstract. Organosulfates (OSs) with ambiguous formation mechanisms are a potential source of missing secondary organic aerosol (SOA) in current atmospheric models. In this study, we chemically characterized OSs and nitrooxy-OSs (NOSs) formed under the influence of biogenic emissions and anthropogenic pollutants (e.g., NOx, SO42−) in summer in Beijing. An ultrahigh-resolution mass spectrometer equipped with an electrospray ionization source was applied to examine the overall molecular composition of S-containing organics. The number and intensities of S-containing organics, the majority of which could be assigned as OSs and NOSs, increased significantly during pollution episodes, which indicated their importance for SOA accumulation. To further investigate the distribution and formation of OSs and NOSs, high-performance liquid chromatography coupled with mass spectrometry was employed to quantify 10 OSs and 3 NOS species. The total concentrations of quantified OSs and NOSs were 41.4 and 13.8 ng m−3, respectively. Glycolic acid sulfate was the most abundant species among all the quantified species, followed by monoterpene NOSs (C10H16NO7S−). The total concentration of three isoprene OSs was 14.8 ng m−3 and the isoprene OSs formed via the HO2 channel were higher than those formed via the NO ∕ NO2 channel. The OS concentration coincided with the increase in acidic sulfate aerosols, aerosol acidity, and liquid water content (LWC), indicating the acid-catalyzed aqueous-phase formation of OSs in the presence of acidic sulfate aerosols. When sulfate dominated the accumulation of secondary inorganic aerosols (SIAs; sulfate, nitrate, and ammonium; SO42− ∕ SIA > 0.5), OS formation would obviously be promoted as the increasing of acidic sulfate aerosols, aerosol LWC, and acidity (pH < 2.8). Otherwise, acid-catalyzed OS formation would be limited by lower aerosol acidity when nitrate dominated the SIA accumulation. The nighttime enhancement of monoterpene NOSs suggested their formation via the nighttime NO3-initiated oxidation of monoterpene under high-NOx conditions. However, isoprene NOSs are presumed to form via acid-catalyzed chemistry or reactive uptake of oxidation products of isoprene. This study provides direct observational evidence and highlights the secondary formation of OSs and NOSs via the interaction between biogenic precursors and anthropogenic pollutants (NOx, SO2, and SO42−). The results imply that future reduction in anthropogenic emissions can help to reduce the biogenic SOA burden in Beijing or other areas impacted by both biogenic emissions and anthropogenic pollutants.