Photometric measurements of spring aerosol optical properties in dust and non-dust periods in China

Aerosol observational data spanning three years (2005–2007) from the Chinese Sun Hazemeter Network (CSHN) were analyzed to characterize the optical properties of spring aerosol particles in dust and non-dust weather conditions. The measurements were segregated and the dates of dust period were chosen by ground-based observations and the National Sand-dust Weather Almanac. Observational data obtained under suitable weather conditions and averaged over 15 sites in the CSHN. The data indicated that the mean spring aerosol optical depth (AOD) increased by 33% in dust weather than in nondust weather over the three years under study. Further, the angstrom exponent (a) decreased by 24% in dust weather compared to in non-dust weather. At dust-source sites, AOD increased by 31% and a decrease by 20%. The atmosphere of dust-source sites is relatively clean, and is generally only contaminated with small quantities of dust particles. Atmospheric aerosols of this region were primarily in the form of coarse mode. Aside from being influenced by dust storms, the atmosphere of both near-source and distant sites displayed a large proportion of man-made aerosols, resulting in a large increase in the AOD and a values. Due to the contribution of sand-dust, the AOD of near-source and distant sites increased by 53% and 23%, respectively, while the value of a was reduced by 22% and 25%, respectively. Due to the content differences of man-made aerosols, and the fact that some observational data cannot be obtained under heavy dust storm weather conditions, the mean AOD and a were highest at distant sites (0.69 and 0.91), intermediate at nearsource sites (0.51 and 0.86), and lowest at the dust-source sites (0.36 and 0.48). In addition, if we take into account the impact of strong dust storms in which AOD can’t be observed by sunphotometer, the AOD probably become greater the farther form the dust-source region in non-dust periods, and while it is opposite in dust periods. Data were also obtained for both urban and ecology background sites. AOD and a values were both significantly higher at urban sites than at neighboring natural ecology background sites during both dust and non-dust periods, but the occurrence of dust process made the multiplier slightly larger. 2008 Elsevier Ltd. All rights reserved.