Non-polar organic compounds in autumn and winter aerosols in a typical city of eastern China: size distribution and impact of gas–particle partitioning on PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; source apportionment

Deming Han,Jian Zhen Yu,Pengfei Cheng,Yong Zhou,Qingyan Fu,Hao Xu,Yingge Ma,Shan Liang,Jinping Cheng,Xiaojia Chen,Li Li,Song Gao,Liping Qiao

doi:10.5194/acp-18-9375-2018

Abstract

Abstract. Aerosol-associated non-polar organic compounds (NPOCs), including 15 polycyclic aromatic hydrocarbons (PAHs), 30 n-alkanes, 2 iso-alkanes, 5 hopanes and 5 steranes, were identified and quantified in PM2.5 samples using the thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS) method. The samples were mainly collected in autumn and winter in a typical city of eastern China. The total concentrations of NPOCs were 31.7–388.7 ng m−3, and n-alkanes were the most abundant species (67.2 %). The heavy-molecular-weight PAHs (four- and five-ring) contributed 67.9 % of the total PAHs, and the middle-chain-length n-alkanes (C25–C34) were the most abundant (72.3 %) in n-alkanes. PAHs and n-alkanes were mainly distributed in the 0.56–1.00 µm fraction, while ∑ (hopanes + steranes) were associated with the 0.32–1.00 µm fraction, suggesting condensation of combustion products was their important origin. The ratio–ratio plots indicated that NPOCs in the local area were affected by photochemical degradation. To reduce the uncertainty caused by only particle NPOC data for source apportionment, the particle and predicted gaseous-phase NPOCs, incorporated with other PM2.5 compound were used as input data for the positive matrix factorization (PMF) model. Eight factors were extracted for both cases: secondary aerosol formation, vehicle exhaust, industrial emission, coal combustion, biomass burning, ship emission, and dust and light NPOCs. These findings highlight the emissions from different aerosol-associated NPOC origins, which caused different size-specific distributions, photodegradation and gas–particle partitioning, which further affect PM2.5 source apportionment. Considering these effects on organic tracers will help us accurately identify the potential sources of aerosols and then asses the contributions from each source.

Highlights

In recent years, severe atmospheric pollution characterized by haze episodes has been a recurring problem in developing countries, affecting visibility, optical radiation and human health (Yadav et al, 2013; Wang et al, 2015; Shen et al, 2015; Sulong et al, 2017)
This study finds generally higher PM2.5associated non-polar organic compounds (NPOCs) concentrations measured in Jiujiang compared to other measurements, which may be due to this study being mainly conducted in the cold season when severe atmospheric pollution episodes frequently occurred
A total of 57 NPOCs were identified in this study (Table 2), including 30 n-alkanes, 2 iso-alkanes, 15 polycyclic aromatic hydrocarbons (PAHs), 5 hopanes and 5 steranes

Summary

Introduction

Severe atmospheric pollution characterized by haze episodes has been a recurring problem in developing countries, affecting visibility, optical radiation and human health (Yadav et al, 2013; Wang et al, 2015; Shen et al, 2015; Sulong et al, 2017). A haze episode is caused by the distribution of particulate matter with different sizes in atmosphere, leading to a decrease in visibility (Xie et al, 2017). Carbonaceous aerosols contain a large amount of particulate matter, accounting for 30–50 % of PM2.5 mass concentrations (Yadav et al, 2013; Wang et al, 2016; Ma et al, 2018). Han et al.: Size distribution and impact of gas–particle partitioning on PM2.5 source apportionment ence on environmental and physical processes, including dry and wet deposition, cloud condensation nucleation and heterogeneous reactions (Feng et al, 2006; Li et al, 2017)

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Conclusion