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

摘要

In order to investigate the chemical characteristics of atmospheric aerosol measured during a severe winter haze event, 12-hr PM_(2.5) (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 PM_(2.5) mass concentration was 105.1 ± 34.9 μg/m~3. Low PM_(2.5) 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 μg/m~3, with a mean of 54.9 ± 25.4 μg/m~3, whereas elemental carbon (EC) concentration ranged from 0.1 to 3.6 μgC/m~3, with a mean of 1.5 ± 0.8 μgC/m~3. 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/m~3. 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. PM_(2.5) 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.