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In order to investigate the chemical characteristics of atmospheric aerosol measured during a severe winter haze event, 12-hr PM2.5(particulate matter with an aerodynamic diameter ≤2.5 μm) samples were collected at an urban site in Ulaanbaatar, Mongolia, from January 9 to February 17, 2008. On average, 12-hr PM2.5mass concentration was 105.1 ± 34.9 μg/m3. Low PM2.5mass concentrations were measured when low pressure developed over central Mongolia. The 12-hr average organic mass by carbon (OMC) varied from 6.4 to 132.3 μg/m3, with a mean of 54.9 ± 25.4 μg/m3, whereas elemental carbon (EC) concentration ranged from 0.1 to 3.6 μgC/m3, with a mean of 1.5 ± 0.8 μgC/m3. Ammonium sulfate was found to be the most abundant water-soluble ionic component in Ulaanbaatar during the sampling period, with an average concentration of 11.3 ± 5.0 μg/m3. In order to characterize the effect of air mass pathway on fine particulate matter characteristics, 5-day back-trajectory analysis was conducted, using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The haze level was classified into three categories, based on the 5-day air mass back trajectories, as Stagnant (ST), Continental (CT), and Low Pressure (LP) cases. PM2.5mass concentration during the Stagnant condition was approximately 2.5 times higher than that during the Low Pressure condition, mainly due to increased pollutant concentration of OMC and secondary ammonium sulfate. [ABSTRACT FROM AUTHOR]

Abstract: The hygroscopic properties of the water-soluble matter extracts of atmospheric aerosols collected at an urban site (47.92° N, 106.90° E, ∼1300m above sea level) in Ulaanbaatar, Mongolia during the cold winter of 2007 were investigated using a hygroscopicity tandem differential mobility analyzer (H-TDMA). Dynamic shape correction factor (χ), the ratio of the actual drag force on a non-spherical aerosol particle to that on a sphere of equivalent volume, of the laboratory generated water-soluble matter (WSM) was found to be 1.09–1.38 (avg. 1.23±0.10), implying that particles generated from the WSM are highly non-spherical. The reduction in the mobility diameter can cause ∼11% underestimation in a hygroscopic growth factor at 85% RH. The hygroscopic growth factors at 85% RH (g(85%)), defined as the ratio of the particle diameter at 85% RH to that at RH<10% (initial dry diameter), of the WSM (initial dry particle diameter=100nm) were 1.32–1.50 (avg. 1.40±0.06). The g(RH) of the water-soluble organic matter (WSOM) was retrieved from the measured g(RH) of the WSM and using the ZSR (Zdanovskii–Stokes–Robinson) approach and the thermodynamic aerosol inorganic model (AIM). We found that the g(85%) of the WSOM were in the range of 1.11–1.35 (avg. 1.22±0.08), which are comparable to those of the biomass burning aerosols. [Copyright &y& Elsevier]