Chemical characteristics of fine particulate matters measured during severe winter haze events in Ulaanbaatar, Mongolia.

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 < or = 2.5 microm) samples were collected at an urban site in Ulaanbaatar Mongolia, from January 9 to February 17, 2008. On average, 12-hr PM2.5 mass concentration was 105.1 +/- 34.9 microg/m3. Low PM2.5 mass 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 microg/m3, with a mean of 54.9 +/- 25.4 microg/m3, whereas elemental carbon (EC) concentration ranged from 0.1 to 3.6 microgC/m3, with a mean of 1.5 +/- 0.8 microgC/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 microg/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. PM2.5 mass 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.