Optical properties and chemical composition of the atmospheric aerosol in urban Guangzhou, China

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• 作者：Meinrat O. Andreae ; Otmar Schmid ; Hong Yang ; Duli Ch ; Jian Zhen Yu ; Li-Min Zeng ; Yuan-Hang Zhang
• 关键词：Aerosol ; Light absorption ; China ; Pearl River Delta ; Chemical composition
• 刊名：Atmospheric Environment
• 出版年：2008
• 出版时间：August 2008
• 年：2008
• 卷：42
• 期：25
• 页码：6335-6350
• 全文大小：487 K

文摘

During the Pearl River Delta measurement campaign (Program of Regional Integrated Experiments of Air Quality over Pearl River Delta 2004, PRIDE-PRD2004, 4 October–5 November 2004), we measured aerosol light absorption and scattering (PM2.5) in urban Guangzhou, using a photoacoustic spectrometer and two integrating nephelometers (at ambient and dry humidity). In addition, 12-h averages of elemental carbon (EC_a), organic carbon (OC), and inorganic species concentrations were determined. Aerosol concentrations in urban Guangzhou were extremely high, with average PM2.5, OC, and EC_a concentrations of 103, 22.4, and 7.1 μg m⁻³, respectively. The chemical composition of the aerosol was dominated by particulate organic matter, EC_a, sulfate and ammonium. Elevated levels of potassium indicated significant contributions from biomass burning to the regional haze. The high average OC/EC_a ratio of 3.6±1.1 resulted from a mixture of regional haze with high OC content and local emissions with low OC/EC_a, mostly from vehicular sources. The average scattering and absorption coefficients for dry aerosol were 418 and 91 Mm⁻¹ (λ540 nm), and the mean mass scattering and absorption efficiencies 4.2±1.0 and 0.78±0.19 m² g⁻¹. During some episodes resulting from the trapping of local emissions in a nocturnal boundary layer, extreme values of aerosol absorption were reached (up to 490 Mm⁻¹). The average single scattering albedo (ω₀, λ540 nm) at dry conditions was about 0.83, representing a mixture of fresh, strongly absorbing, urban pollution, and a more scattering regional haze. Because of the prevailing low humidity, the ambient ω₀ was not significantly higher. The mass absorption efficiency of EC_a was 7.7 m² g⁻¹; an additional contribution to absorption was associated with OC, either as a result of light absorption by OC or the effects of internal mixing. The observed diurnal trends of the optical and chemical properties are consistent with aged regional haze dominating during mid-day, enhanced traffic activity in the morning and evening hours, and the build-up of a shallow nocturnal boundary layer during night.