The Optical Properties And Chemical Composition Of Aerosols In Shanghai

Aerosols play an important role in the global climate system through modifications of the global radiation budget. And it also has a severe effect on air quality and human health as one of the important air pollutants of urban area. Thus, the study of aerosol optical properties and its vertical distribution is critical for air pollution control and better understanding of the aerosol radiative forcing. The vertical distributions, optical properties and chemical composition of aerosols over Shanghai were analyzed using data from both ground-based observation and space remote sensing.Based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation/Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO/CALIOP) retrieval, aerosol vertical extinction (σ) profile were classified into near-surface, mixed, multilayer transport and uplifted near-surface types. The results denote the effects of aerosols from local sources or/and transported from remote sources on aerosol loadings and discussed in consideration of temperature, relatively humidity and wind shears. All the three factors have different effect on σ profiles, and temperature is the most obviously one especially when inversion happens. According to the5-day backward trajectories, local pollution is the main source of type I and II profiles, while type III profiles represent the effect of both long-range transport of aerosols and local emissions. And the formation of type IV t profiles might be related to the insufficient mix of pollutants from both local emission and long-range transport. The frequency distribution of σ shows no significant seasonal variation, and the high values of σ appear within the altitude of2km. Aerosols with high altitude contribute less to the aerosol extinction in Shanghai.Measurements of spectral aerosol optical depth (AOD) were carried out at Shanghai using a hand-held multi-band sun photometer MICROTOPS II from November2009to October2010. AODs were almost in low level during the entire experiment with maximum0.69in November and minimum0.24in August. Both the AODs and Angstrom exponents(a) showed a clear pattern of seasonal variation, awere commonly exceeding1.30, indicating that fine particles mainly contributed to aerosol loading except springtime. Comparison of retrieved AODs derived from CALIPSO/CALIOP and sun photometer shows a general agreement with AODobservation=AODCALIPSO/CALIOP×0.97+0.08(R2=0.59), and CALIOP data appears to underestimate the values of AOD. The distribution of CALIPSO/CALIOP derived AODs for different heights in troposphere were analyzed. The result shows an obviously pattern of seasonal variation. The near-surface aerosol layer contributes the most to the columnar AOD.The study of the correlation between CALIPSO/CALIOP derived AODs and aerosol chemical composition shows the importance of the secondary aerosol. However, when the pollution characteristics are complex, the correlation coefficients of AODs and the concentrations of water-soluble ions in PM2.5/trace gases become very low, which means it only can obtain very limited information about the correlation between AODs and aerosol chemical composition by linear regression analvsis for this kind of situation.