Vertical distribution of particle-phase dicarboxylic acids, oxoacids and &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-dicarbonyls in the urban boundary layer based on the 325 m tower in Beijing

Wanyu Zhao,Lianfang Wei,Xin Zeng,Zifa Wang,Qiaorong Xie,Shaofei Kong,Huiyun Du,Pingqing Fu,Siyao Yue,Kimitaka Kawamura,Hong Ren,Yele Sun,Xueshun Chen,Ping Li

doi:10.5194/acp-20-10331-2020

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.

Highlights

Organic aerosols typically make up 20 %–50 % of the mass concentrations of atmospheric fine aerosols (PM2.5) at continental mid-latitudes
This study investigates, for the first time, the vertical distributions of Low molecular weight (LMW) dicarboxylic acids, oxoacids and αdicarbonyls in PM2.5 collected at Beijing during August to September 2015, along with analyses of ions, watersoluble organic carbon (WSOC), organic carbon (OC), elemental carbon (EC), and tracer compounds like levoglucosan and isoprene-oxidation products
Previous studies found that relatively large OC / EC ratio is associated with biomass burning (7.3), whereas a lower value is linked to vehicular exhausts (1.1) (Sandradewi et al, 2008)

Summary

Introduction

Organic aerosols typically make up 20 %–50 % of the mass concentrations of atmospheric fine aerosols (PM2.5) at continental mid-latitudes. A large portion of organic aerosol is water soluble, contributing 20 %–75 % to the carbon mass of aerosols emitted from uncompleted combustion sources (Falkovich et al, 2005; Pathak et al, 2011; Graham et al, 2002). W. Zhao et al.: Vertical distribution of particle-phase dicarboxylic acids, oxoacids and α-dicarbonyls related compounds are water soluble and are found abundantly in urban (Wang et al, 2012; Zhao et al, 2018), mountainous (Kawamura et al, 2013; Cong et al, 2015), remote marine Zhao et al.: Vertical distribution of particle-phase dicarboxylic acids, oxoacids and α-dicarbonyls related compounds are water soluble and are found abundantly in urban (Wang et al, 2012; Zhao et al, 2018), mountainous (Kawamura et al, 2013; Cong et al, 2015), remote marine (Mochida et al, 2007; H. Wang et al, 2006; Fu et al, 2013a; Yang et al, 2020), and Arctic (Kawamura et al, 2010, 1996) aerosols and in snow, rain, and fog waters (Sempére and Kawamura, 1994; Kawamura et al, 2001; Zhao et al, 2019a, b)

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Results

Conclusion