Air pollution and meteorological processes in the growing dryland city of Urumqi (Xinjiang, China) Original Research Article

Seven years (2000–2006) of monthly PM10 (particulate matter, d ≤ 10 μm), SO2, and NO2 concentrations are reported for Urumqi, the capital of Xinjiang in NW China. Considerably high mean annual concentrations have been observed, which ranged between 150 and 240 μg m− 3 (PM10), 31 and 50 μg m− 3 (NO2), and 49 and 160 μg m− 3 (SO2). The shapes of seasonal variation of all pollutants were remarkably similar; however, winter/summer ratios of concentrations were quite different for PM10 (2–3) and NO2 (≈ 4) compared to SO2 (up to 30). Very high consumption rates of fossil fuels for energy generation and domestic heating are mainly responsible for high annual pollution levels, as well as the (very) high winter/summer ratios. Detailed analysis of the 2000–2006 records of Urumqiʹs meteorological data resulted in inter-annual and seasonal frequency distributions of (a) (surface) inversion events, (b) heights of surface inversions, (c) stability classes of Urumqiʹs boundary layer, and (d) the “Air Stagnation Index (ASI)”. Urumqiʹs boundary layer is shown to be characterized by high mean annual and seasonal frequencies of (surface) inversions and by the dominance of stable dispersion classes. A further outcome of the meteorological analysis is the proof of Urumqiʹs strong diurnal wind system, which might have particularly contributed to the stabilization of the nocturnal boundary layer. Annual and seasonal variations of pollutantʹs concentrations are discussed in the context of occurrences of inversions, boundary layer, stability classes, and ASI. The trend of Urumqiʹs air pollution indicates a strong increase of mean annual concentrations 2000–2003, followed by a slight increase during 2003–2006. These are in strong contrast to (a) the growth of Urumqiʹs fleet of motor vehicles and (b) to the growing number of stable regimes of Urumqiʹs boundary layer climate during same period. It is concluded that the (regional and) local administrative technical countermeasures have efficiently lowered Urumqiʹs air pollution levels.