Characteristics of Air Pollution Index in Urumqi From 2002 to 2011
Based on the daily data of air pollution index(API) and the ground meteorological variables of corresponding period from 2002 to 2011, this paper has researched change characteristics of API and the correlations between API and meteo-rological variables in Urumqi. The conclusions are as follows: During the period of 2002 and 2011, the air pollution conditions have been improved gradually. The annual coefficient of API variation of-3.2. The proportion of air quality excellent varied between 59.1% to 77.4%, and the air quality in summer is the best and in winter is the worst among four seasons. The number of days in Class Ⅰ accounted for 9.34% ~34.82% of total number of days in the spring, summer and autumn. The number of days in Class Ⅲ and above is very much in winter, which reaching 82.97% of total number of days. The monthly average API has a positive correlation with air pressure and relative humidily while it has a negative correlation with wind speed, air temperature, average vapor pressure and sunshine hours. Under seasonally average size, the correlation coefficient between API and meteorological vaiables are consistent with monthly average API, and the correlation coefficient has increased significantly. The correlation coefficient between API and meteorological vaiables have larger change in the different levels of pollution. According to an analysis of the distribution of pollution days for different wind directions, Urumqi is mainly influenced by extreme wind speed and maximum wind speed from north-northwest and north in non-pollution days while from north-northeast and east in pollution days.