In 2011, using Chinese statistics, the World Health Organization reported that Lanzhou had the worst air quality (annual mean PM10 ug/m3 of 150) among eleven western Chinese cities, and was worse than Beijing with its reading of 121.
2011 年，根据中国数据，世界卫生组织报告，兰州在中国西部城市中空气质量最差（年平均 PM10 为 150 ug/m3），比北京（数值为 121）还差。