Seasonal variations of transport pathways and potential sources of PM_2.5 in Chengdu, China (2012–2013)

Highlights

PM_2.5 in Chengdu showed clear seasonal and diurnal variation.

5, 5, 5 and 3 mean clusters are generated in spring, summer, autumn, and winter.

Short-distance air masses are important pathways in Chengdu.

Emissions within the Sichuan Basin contribute significantly to PM_2.5 pollution.

Long-range transport from Southern Xinjiang is a dust invasion path to Chengdu.

Abstract

Seasonal pattern of transport pathways and potential sources of PM_2.5 in Chengdu during 2012–2013 were investigated based on hourly PM_2.5 data, backward trajectories, clustering analysis, potential source contribution function (PSCF), and concentration-weighted trajectory (CWT) method. The annual hourly mean PM_2.5 concentration in Chengdu was 97.4 mg·m^–3. 5, 5, 5 and 3 mean clusters were generated in four seasons, respectively. Short-distance air masses, which travelled within the Sichuan Basin with no specific source direction and relatively high PM_2.5 loadings (>80 mg·m^–3) appeared as important pathways in all seasons. These short pathways indicated that emissions from both local and surrounding regions of Chengdu contributed significantly to PM_2.5 pollution. The cities in southern Chengdu were major potential sources with PSCF>0.6 and CWT>90 mg·m^–3. The northeastern pathway prevailed throughout the year with higher frequency in autumn and winter and lower frequency in spring and summer. In spring, long-range transport from southern Xinjiang was a representative dust invasion path to Chengdu, and the CWT values along the path were 30-60 mg·m^–3. Long-range transport was also observed in autumn from southeastern Xinjiang along a northwesterly pathway, and in winter from the Tibetan Plateau along a westerly pathway. In summer, the potential source regions of Chengdu were smaller than those in other seasons, and no long-range transport pathway was observed. Results of PSCF and CWT indicated that regions in Qinghai and Tibet contributed to PM_2.5 pollution in Chengdu as well, and their CWT values increased to above 30 mg·m^-3 in winter.

Graphical abstract

Keywords

Transport pathway / Backward trajectory / Clustering analysis / Potential source / Chengdu

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Acknowledgements

This study was funded by the public grant from the Ministry of Environmental Protection of China (Characteristics and Controlling Measures of Atmospheric Haze in the Cheng-Yu Region, No. 201009001), the funds for young talents from Beijing Municipal Government (No. 2014000020124G119), and the Funds for Excellent Teachers from Capital University of Economics and Business (2016). We would like to thank Sichuan Provincial Environmental Monitoring Center for providing the on-line PM_2.5 data.

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