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 PM2.5 and the structure of the atmospheric boundary layer (ABL) during the 2010 heating season. The concentration of PM2.5 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 PM2.5 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 PM2.5 in winter.
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机译：蒙古首都乌兰巴托在冬季受到大气污染的严重影响，这严重影响了裸露人群的健康。利用激光雷达和地面气象观测，我们研究了2010年加热季节期间PM2.5的时间变化和大气边界层（ABL）的结构。在10月8-10日和21-25日发生两次冷浪期间，气温急剧下降之后，PM2.5的浓度增加。由于10月10日开始的寒潮，地表空气温度首次降至0°C以下，这促使ger（蒙古传统民居）地区的家庭开始燃烧煤炭供暖，导致PM2.5浓度升高。同时，当天气受西伯利亚高压影响时，从夏季到冬季，最大ABL高度连续下降，并在第二次冷浪之后降至800 m以下。冬季稳定的大气条件和地表反转层导致低风速（<2 m s？1），尤其是在夜间。因此，由于气象和地形条件，空气污染物仍停留在城市地表水平，导致冬季PM2.5浓度很高。
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