Air Particulate Pollution in Ulaanbaatar, Mongolia: Variation in Atmospheric Conditions from Autumn to Winter

Abstract

Ulaanbaatar, the capital city of Mongolia, is subject to high levels of atmospheric pollution during the winter, which severely effects the health of the exposed population. Using lidar and ground level meteorological observations, we studied the temporal variation of the PM_2.5 and the structure of the atmospheric boundary layer (ABL) during the 2010 heating season. The concentration of PM_2.5 increased after the air temperatures sharply decreased during two cold waves occurring 8-10 and 21-25 October. The surface air temperatures first dropped below 0°C because of the cold wave beginning on 10 October, which prompted the households in the ger (traditional Mongolian dwelling) districts to start combusting coal for heating, resulting in increased PM_2.5 concentrations. Meanwhile, the maximum ABL height continuously decreased from summer to winter and dropped below 800 m after the second cold wave, when the weather was influenced by a Siberian high. The stable atmospheric conditions and surface inversion layer in winter resulted in low wind velocities (< 2 m s⁻¹), especially at night. Consequently, because of both the meteorological and topographical conditions, air pollutants remained at the urban surface level, which resulted in high concentrations of PM_2.5 in winter.