Measurement of aerosol chemical, physical and radiative properties in the Yangtze delta region of China


In order to understand the possible influence of aerosols on the environment in the agricultural Yangtze delta region of China, a one-month field sampling campaign was carried out during November 1999 in Linan, China. Measurements included the aerosol light scattering coefficient at 530 nm, σsp, measured at both dry relative humidity (RH < 40%) and under ambient conditions (sample RH = 63 ± 19%), and the absorption coefficient at 565 nm, σap, for aerosol particles having diameters < 2.5 μm (PM2.5). At the same time, daily filter samples of PM2.5 as well as aerosol particles having diameters < 10 μm (PM10) were collected and analyzed for mass, major ion, organic compound (OC), and elemental carbon (EC) concentrations in order to determine which anthropogenic chemical species were primarily responsible for aerosol light extinction. The aerosol loading in the rural Yangtze delta region was comparable to highly polluted urban areas, with mean and standard deviation (S.D.) values for σsp, σap and PM2.5 of 353 Mm-1 (202 Mm-1), 23 Mm-1 (14 Mm-1) and 90 μg m-3 (47 μg m-3), respectively. A clear diurnal pattern was observed in σsp and σap with minimum values occurring in the middle of the day, most likely associated with the maximum midday mixing height. The ratio of the change in light scattering coefficient at ambient RH to that at controlled RH (RH < 40%), Fσsp (RH), indicates that condensed water typically contributed ∼40% to the light scattering budget in this region. The mass scattering efficiency of the dry aerosol, Escat_2.5, and mass absorption efficiency of EC, Eabs_2.5, have mean and S.D. values of 4.0 m2 g-1 (0.4 m2 g-1) and 8.6 m2 g-1 (7.0 m2 g-1), respectively. PM2.5 concentrations in Linan and two other locations in the Yangtze delta, Sheshan and Changshu (which have monthly mean values ranging from ∼80 to 110 μg m-3), are all significantly higher than the proposed 24-h average US PM2.5 NAAQS of 65 μg m-3. Organic compounds are the dominant chemical species accounting for ∼50% of the PM2.5 mass at all three sites. The results indicate that aerosol loadings in the agricultural Yangtze delta region of China are relatively high, and suggest that aerosols have a significant impact on visibility, climate, crop production, and human health in this region. © 2002 Elsevier Science Ltd. All rights reserved.