Aerosol chemical, physical, and radiative characteristics near a desert source region of northwest China during ACE‐Asia

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The Gobi desert in northwest China is an important source of mineral aerosols over both eastern Asia and the northern Pacific Ocean. In order to determine the chemical, physical, and radiative properties of aerosols originating from the Gobi desert source region, field measurements were performed in Yulin, China, in April 2001 as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) campaign. The means and standard deviations of the measured aerosol light absorption coefficient σap, scattering coefficient σsp, and single‐scattering albedo ω are 6 Mm−1 (11 Mm−1), 158 Mm−1 (193 Mm−1), and 0.95 (0.05), respectively. A clear diurnal pattern is observed in both σap and σsp, resulting from diurnal changes in the mixing height as well as from local combustion sources in the morning and dust sources in the afternoon. Two distinct populations of aerosol mass scattering efficiencies Escat_2.5, one for aerosols dominated by desert dust (∼1.0 m2 g−1) and the other for aerosols composed primarily of local pollutants (∼3.0 m2 g−1), are observed. During the field study there were three significant dust events that occurred for, on average, several days at a time. The most significant dust storm resulted in a 24‐hour‐average PM2.5 concentration (mass concentration of particles having aerodynamic diameters less than 2.5 μm) of 453 μg m−3 and a peak σsp of 2510 Mm−1 on 8 April. The mean PM2.5 mass concentration during the dust storm periods is approximately 169 μg m−3, about 4 times greater than the mean value of 44 μg m−3 observed during local pollution periods. When local pollution is the dominant source of fine particulate mass, organic matter (OM) is the major chemical component, contributing 41% to the PM2.5 mass, followed by crustal material (29%), sulfate (17%), and elemental carbon (EC) (13%). During sand storm periods, ∼51% of PM2.5 mass is crustal material, followed by CO32− (11%) and OM (9.5%). The element enrichment factors indicate that coal combustion, biomass burning, and mobile source emissions are important local pollution sources. Overall, our results indicate that in addition to dust, local pollution also has a significant influence on aerosol properties in the region.