Abstract
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 (
λ∼540
nm), and the mean mass scattering and absorption efficiencies 4.2±1.0 and 0.78±0.19
m
2
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 (
ω
0,
λ∼540
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
ω
0 was not significantly higher. The mass absorption efficiency of EC
a was 7.7
m
2
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.