A STUDY OF OPTICAL, PHYSICAL AND CHEMICAL PROPERTIES OF AEROSOLS USING IN SITU MEASUREMENTS
Abstract
Using a simple sampling apparatus, aerosol particles were collected on a polycarbonate substrate in various locations around the world. The focus of this study was Xianghe, China, an industrial town 70 km southeast of Beijing. The Nuclepore filters were collected in two size ranges (coarse, 2.5μm < d < 10μm, and fine, d < 2.5μm) from January-December 2005, with a focus on the Intensive Observation Campaign (IOC) in March 2005.
The collected filters were analyzed for aerosol mass concentration and aerosol absorption efficiency; selected filters were analyzed for chemical composition. For fine mode aerosols measured during the Xianghe 2005 IOC, the average spectral absorption efficiency equates well to a &lamda;-1 model, while the coarse mode shows a much flatter spectral dependence, consistent with large particle models. The coarse mode absorption efficiency was compatible with that of the fine mode in the near-IR region, indicating the much stronger absorption of the coarse mode due to its composition and sizeable mass.
Ground-based measurements were compared to remote sensing instruments that measure similar parameters for the total column. A co-located lidar assisted in determination of vertical homogeneity. For cases of vertical homogeneity, the ground-based measurements were able to represent total column measurements well. For cases of vertical inhomogeneity, ground-based measurements did not equate well to total column measurements.
The layers of aerosols that form in the atmosphere have significant effects on the temperature profile. An instrument was developed to measure aerosol absorption and scattering, the Scattering and Absorption Sonde (SAS). This instrument was launched seven times at two locations in China in 2008. Vertical profiles of scattering coefficient were measured and several aerosol layers were identified.
The aerosol characterized at Xianghe, China was compared to aerosol characteristics from Kanpur, India and Mexico City, Mexico. The aerosol at Mexico City differs greatly from that at Xianghe, based on the measured mass concentration, aerosol size distribution from AERONET, and measured aerosol absorption efficiency. The aerosol at Kanpur resembles well the aerosol characterized at Xianghe in the fine mode, with a correlation of 0.998 for the aerosol absorption efficiency.