Reconstructed light extinction coefficients of fine particulate matter in rural Guangzhou, southern China

A one-year campaign was conducted to collected PM2.5samples 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 bextwas compared with the measured bextconverted from visibility. A good correlation was obtained between the two sets of bextwith a coefficient of determination (R2) of 0.61 and a slope of 0.99. The average reconstructed bextin the study was 253.7 ± 162.9 Mm–1. The seasonal reconstructed bextwas 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 bextand measured bextwas investigated under the influence of seasonality, visibility and PM2.5concentration. We found that bextcould be reconstructed using revised IMPROVE formula in high PM2.5days (threshold value of ~60 μg m–3). On other hand, the performance of formula was unsatisfactory for bextreconstruction of in low PM2.5days, when meteorological conditions could have significant impact on visibility.