[Observation and analysis of air pollution in Zhangjiakou, Hebei].

Zhangjiakou is an important city in the north of Hebei province with rapidly developing industry in recent years, which has little precipitation and a very fragile ecological environment. The observation of atmospheric pollutants was done from December 2009 to November 2010 to illuminate the air pollution situation. The results showed that the annual mean concentration of PM10, the primary pollutant, reached (137 +/- 105) microg x m(-3), and those of NO, NO2, SO2 and O3 were (8 +/- 13), (30 +/- 15), (19 +/- 26) and (54 +/- 35) microg x m(-3), respectively; The seasonal mean concentrations of NOx and SO2 were highest in winter, with values of (51 +/- 35) microg x m(-3) and (42 +/- 29) microg x m(-3), respectively, and lowest in summer, only (28 +/- 8) and (4 +/- 3) microg x m(-3), respectively. For O3, the highest value was recorded in summer, with seasonal mean of (92 +/- 40) microg x m(-3) and the highest daily maximum hourly concentration of 271 microg x m(-3), whereas the lowest seasonal mean value of (34 +/- 20) microg x m(-3) was obtained in winter. The highest seasonal average PM10 was measured in spring, reaching (144 +/- 131) microg x m(-3), and lowest in winter, with a value of (130 +/- 129) microg x m(-3), indicating little seasonal variation of PM10. The rate that PM10 exceeded the National Ambient Air Quality Standard II was 28%. The diurnal variations of pollutants in four seasons showed that the average diurnal variations of NO, and PM10 were similar with peaking in early morning and evening, while the peak of SO2 and O3 appeared at noon and in the afternoon, respectively. The diurnal variation of air pollutants was significantly affected by the traffic, and the seasonal variation of gas pollutants was significantly affected by coal-fired heating in winter. In summer, the air masses from southeast regions could transport O3 and its precursors to Zhangjiakou. Dust carried by northwestern air masses and local dust with strong winds greatly affected PM10 in Zhangjiakou, and North China Plain was also affected in some degree.