Day-Night Differences, Seasonal Variations and Source Apportionment of PM10-Bound PAHs over Xi’an, Northwest China

Xin Wang,Yali Lei,Junji Cao,Hongmei Xu,Zhenxing Shen,Fobang Liu,Yaling Zeng,Liu Yang,Qian Zhang

doi:10.3390/atmos9020062

Abstract

Day-night PM10-bound PAHs were studied at an urban site of Xi’an from 20 December 2006 to 28 October 2007. The annual mean concentration of nighttime PAHs (285.0 ng m−3) was higher than that in daytime (239.4 ng m−3). A significant difference of PAH concentrations between daytime and nighttime was found in autumn with a coefficient of divergence (CD) of 0.23 (significant level 0.2). However, no distinct difference was observed in other seasons (with CD values < 0.2), although the difference of PAHs partition capacity in PM10 between daytime and nighttime was significant in the four seasons. Remarkable seasonal variations were observed in the total PAH levels, with a highest mean concentration of 344.6 ng m−3 in winter and a lowest mean concentration of 177 ng m−3 in summer. Positive matrix factorization results revealed that residential emission for heating is the major contributor of the elevated PAH levels in winter, accounting for 49% of the total PAH levels. The coal combustion including industrial and residential usage, contributed over 40% of the PAH emissions in PM10 of Xi’an during the one-year sampling period. These results can provide guidance for taking measures in reducing PAHs levels in the air.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) are a group of ubiquitous air pollutants, primarily emitted from incomplete combustion of almost any fuels
PM10 -bound PAHs were investigated on their abundance, day–night differences, seasonal variations and potential emission sources in Xi’an, based on a year-round dataset
A significant difference of PAHs concentrations between daytime and nighttime was found in autumn, while the differences were insignificant in other seasons

Summary

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a group of ubiquitous air pollutants, primarily emitted from incomplete combustion of almost any fuels. They are of great concern mainly because of their carcinogenic and mutagenic properties. To reduce the potential health risk of PAHs, efforts on numerous modelling and field investigations have been made to elucidate the sources, spatiotemporal distributions as well as transformations and fate of PAHs in the atmosphere [4,5,6]. As semi-volatile organic compounds (SVOCs), PAHs may undergo gas-particle partitioning once emitted into the atmosphere, which is strongly influenced by ambient temperature [5,8,9]. The abundance and profiles of PAHs in ambient air are

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