Vertical distribution of particle-phase dicarboxylic acids, oxoacids and α-dicarbonyls in the urban boundary layer based on the 325 m tower in Beijing

Abstract

Abstract. Vertical distributions of dicarboxylic acids, oxoacids, α-dicarbonyls and other organic tracer compounds in fine aerosols (PM2.5) were investigated at three heights (8, 120 and 260 m) based on a 325 m meteorological tower in urban Beijing in the summer of 2015. Results showed that the concentrations of oxalic acid (C2), the predominant diacid, were more abundant at 120 m (210±154 ng m−3) and 260 m (220±140 ng m−3) than those at the ground surface (160±90 ng m−3). Concentrations of phthalic acid (Ph) decreased with the increase in height, indicating that local vehicular exhausts were the main contributor. Positive correlations were noteworthy for C2 ∕ total diacids with mass ratios of C2 to main oxoacids (Pyr and ωC2) and α-dicarbonyls (Gly and MeGly) in polluted days (0.42≤r2≤0.65), especially at the ground level. In clean days, the ratios of carbon content in oxalic acid to water-soluble organic carbon (C2−C ∕ WSOC) showed larger values at 120 and 260 m than those at the ground surface. However, in polluted days, the C2−C ∕ WSOC ratio mainly reached its maximum at ground level. These phenomena may indicate the enhanced contribution of aqueous-phase oxidation to oxalic acid in polluted days. Combined with the influence of wind field, total diacids, oxoacids and α-dicarbonyls decreased by 22 %–58 % under the control on anthropogenic activities during the 2015 Victory Parade period. Furthermore, the positive matrix factorisation (PMF) results showed that the secondary formation routes (secondary sulfate formation and secondary nitrate formation) were the dominant contributors (37 %–44 %) to organic acids, followed by biomass burning (25 %–30 %) and motor vehicles (18 %–24 %). In this study, the organic acids at ground level were largely associated with local traffic emissions, while the long-range atmospheric transport followed by photochemical ageing contributed more to diacids and related compounds in the urban boundary layer than the ground surface in Beijing.

Measurement report: Vertical distribution of biogenic and anthropogenic secondary organic aerosols in the urban boundary layer over Beijing during late summer

“…Similar to the air mass footprints (Fig. S2), these results suggest that the air masses from the southern region significantly contributed to the haze pollution in Beijing (Zheng et al, 2015;Tian et al, 2019).…”

“…In the last decade, severe air pollution in China has attracted worldwide attention (An et al, 2019;Huang et al, 2020a). The haze episodes in China are suggested to result from a complex interplay of anthropogenic emissions, atmospheric processes, regional transport, meteorological conditions, and climatic conditions (An et al, 2019;Zheng et al, 2015;Sun et al, 2016;Du et al, 2021;Huang et al, 2020b). The high contribution of secondary aerosols to the PM pollution during haze events in China highlights the urgent need to understand the compositions and processes of SOA formation in the atmosphere (An et al, 2019;.…”

“…The high contribution of secondary aerosols to the PM pollution during haze events in China highlights the urgent need to understand the compositions and processes of SOA formation in the atmosphere (An et al, 2019;. Previous studies have reported the chemical characteristics of OA in many regions in China (Simoneit et al, 1991;Wang et al, 2006;Xie et al, 2020;Li et al, 2018). However, studies characterizing the vertical properties of SOA in the urban boundary layer are lacking, which constrains research on the interactions of aerosols and regional transport, local emissions, atmospheric processes, and meteorological conditions in urban areas.…”

“…Daily PM 2.5 samples were synchronously collected at three heights (8, 120, and 260 m a.g.l., respectively) based on a 325 m meteorological tower in urban Beijing during the period 15 August to 10 September 2015. Observations at 8 m are more subject to local emissions, whereas those at 120 and 260 m are more representative of mixing and/or regional-scale influences (Sun et al, 2015;Zhao et al, 2020). BSOA and ASOA tracers in PM 2.5 were quantified by gas chromatography and mass spectrometry (GC/MS); organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) in PM 2.5 were also determined.…”

Comment on acp-2021-136

“…Daily PM2.5 samples were synchronously collected at three heights (8 m, 120 m and 260 m, above ground level, respectively) based on a 325-m meteorological tower in urban Beijing during the period 15 th August to 10 th September 2015. Observations at 8 m are more subject to local emissions whereas those at 120 m and 260 m are more representative mixing and/or regional scale influences Zhao et al, 2020). BSOA and ASOA tracers in PM2.5 were quantified by gas chromatograph/mass spectrometry (GC/MS); organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) in PM2.5 were also determined.…”