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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 sigma(ap), scattering coefficient sigma(sp), and single-scattering albedo omega 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 sigma(ap) and sigma(sp), 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 E-scat_2.5, one for aerosols dominated by desert dust (similar to1.0 m(2) g(-1)) and the other for aerosols composed primarily of local pollutants (similar to3.0 m(2) 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 mum) of 453 mug m(-3) and a peak sigma(sp) of 2510 Mm(-1) on 8 April. The mean PM2.5 mass concentration during the dust storm periods is approximately 169 mug m(-3), about 4 times greater than the mean value of 44 mug 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, similar to51% 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.