Recent Atmospheric NO_2 Concentration Dynamics of Lhasa City

The variability of NO_2 mass concentration in the air of Lhasa city was analyzed based on the automatically monitoring data from July 2000 to June 2004.It was shown that the NO_2 mass concentration in the air of Lhasa city remained below the first degree according to the Standard of Ambient Air Quality(GB3095-1996),but was increasing in recent years.The seasonal variation of NO_2 mass concentration in the air was that it was higher in the winter(October to January) than in the other months,the highest NO_2 mass concentration emerged in December,and the monthly average of NO_2 mass concentration from October to the next January exceeded the year's mean.The monthly average NO_2 mass concentration showed a typical U shape.And daily variation showed two peaks of NO_2 mass concentration in the time period of from 8:00 to 12:00 and from 20:00 to 24:00.The car emission and fuel burning in daily life were the main sources of NO_2 around the Lhasa city at present in terms of human devotion,and the special weather condition in the aerosphere was another factor that affected the variability of NO_2 mass concentration in the city.