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Reconstructed Light Extinction Coefficients of Fine Particulate Matter in Rural Guangzhou, Southern China

Category: Optical/Radiative Properties and Remote Sensing

Volume: 16 | Issue: 8 | Pages: 1981-1990
DOI: 10.4209/aaqr.2016.02.0064
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Xiaojia Chen1, Senchao Lai 1,4, Yuan Gao2, Yingyi Zhang 1, Yan Zhao1, Duohong Chen3, Junyu Zheng1, Liuju Zhong3, Shun-Cheng Lee2, Bing Chen1

  • 1 School of Environment and Energy, South China University of Technology, Guangzhou, China
  • 2 Department of Civil and Environmental Engineering, Research Center for Environmental Technology and Management, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China
  • 3 Guangdong Provincial Environmental Monitoring Center, Guangzhou, China
  • 4 Department of Multiphase Chemistry, Max Planck Institute for Chemistry, Mainz, Germany

Highlights

bext of PM2.5 is estimated using the revised IMPROVE formula in rural Guangzhou.
Significant correlation between measured bext and estimated bext was observed.
bext could be reconstructed using revised IMPROVE formula in high PM2.5 days.


Abstract

A one-year campaign was conducted to collected PM2.5 samples in the rural area of Guangzhou, the largest megacity in South China, from March 2012 to February 2013. Mass concentration of PM2.5, carbonaceous fractions (i.e., organic carbon (OC) and elemental carbon (EC)) and 6 water-soluble ions were analyzed. Light extinction coefficient (bext) of fine particulate matter was reconstructed using the revised IMPROVE formula at the site. The reconstructed bext was compared with the measured bext converted from visibility. A good correlation was obtained between the two sets of bext with a coefficient of determination (R2) of 0.61 and a slope of 0.99. The average reconstructed bext in the study was 253.7 ± 162.9 Mm–1. The seasonal reconstructed bext was in the order of autumn (319.4 ± 207.2 Mm–1) > winter (269.6 ± 175.5 Mm–1) > summer (219.0 ± 129.3 Mm–1) > spring (193.3 ± 94.9 Mm–1). (NH4)2SO4 (AS) made a dominant contribution to the light extinction budget, accounting for 61.3% (155.6 ± 108.5 Mm–1) annually, with highest in autumn (68.0%) and lowest in winter (55.2%). Organic matter (OM) was the second largest contributor accounting for 20.5% (52.2 ± 42.7 Mm–1) with highest in winter (23.4%) and lowest in spring (18.0%). The relationship between reconstructed bext and measured bext was investigated under the influence of seasonality, visibility and PM2.5 concentration. We found that bext could be reconstructed using revised IMPROVE formula in high PM2.5 days (threshold value of ~60 µg m–3). On other hand, the performance of formula was unsatisfactory for bext reconstruction of in low PM2.5 days, when meteorological conditions could have significant impact on visibility.

Keywords

PM2.5 Chemical composition Reconstructed light extinction coefficient Revised IMPROVE formula Visibility


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