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 Urumqi's meteorological data resulted in inter-annual and seasonal frequency distributions
of (a) (surface) inversion events, (b) heights of surface inversions, (c) stability
classes of Urumqi's boundary layer, and (d) the "Air Stagnation Index (ASI)". Urumqi's
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 Urumqi's strong diurnal wind
system, which might have particularly contributed to the stabilization of the nocturnal
boundary layer. Annual and seasonal variations of pollutant's concentrations are discussed
in the context of occurrences of inversions, boundary layer, stability classes, and
ASI. The trend of Urumqi's 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 Urumqi's fleet of motor vehicles and (b) to
the growing number of stable regimes of Urumqi's boundary layer climate during same
period. It is concluded that the (regional and) local administrative technical countermeasures
have efficiently lowered Urumqi's air pollution levels.