Abstract:

Based on L-band radar and conventional observation data in Urumqi city from 2007 to 2017,the maximum daily boundary layer height was estimated using the principle of Holzworth dry adiabatic curve,and the corresponding average wind speed and ventilation volume of the boundary layer were calculated.Meanwhile,the air pollution index (AQI) from 2015 to 2017 was used to discuss the relationship between air quality and atmospheric boundary layer parameters.The results show that the average annual height of the maximum daily boundary layer is 1415 m,and demonstrates a downward trend,with an average decline rate of 5.9 m·a^-1.In time series,the daily maximum boundary layer height distribution shows obvious periodicity.The monthly data presents a "parabola",with the lowest average height in January (336 m) and the highest average height in June (2400 m).In winter,the average wind speed of the boundary layer is the smallest,with 2.6 m·s^-1,and the largest in spring and summer,with 5.6 m·s^-1.In a year,the average ventilation volume in January is the smallest,which is 977.0 m²·s^-1,and the average ventilation volume in May is the largest,which is 14835.9 m²·s^-1.From April to September,the average ventilation volume is 13282.3 m²·s^-1.The accumulation of atmospheric pollutants under the conditions of weak wind speed,low boundary layer height,and small ventilation volume is easy to cause moderate pollution.In winter,Urumqi is always located at the rear or bottom of Mongolia high pressure,which is one of the important causes for serious pollution in winter.

Key words: Dry adiabatic, Daily maximum boundary layer height, Average wind speed, Ventilation volume