Interdecadal Change in Frequency of Dust-Haze Episodes in North China Plain
京津冀平原地区灰霾天气的年代变化

The authors report on the first-time use of 1961-2006 hourly visibility data from 15 airports to investigate the interdecadal variation of dust-haze episodes in the North China Plain. The preliminary results show that (1) the evolution of the frequency of dust-haze weather showed interdecadal change characteristics from the 1990s until recent years, with dust-haze episodes evolving from local to regional scale. (2) Between the 1970s and 1990s the frequency of dust-haze episodes increased in the megacities (e.g. Beijing, Shijiazhuang), while decreasing in mid-size and small cities; this has important implication for dust-haze control strategies. (3) Before the 1970s the frequency of dust-haze episodes in the Beijing area (about 100 days per year) was almost the same as in the Shijiazhuang area; however, after 1975 the dust-haze episode frequency in the Shijiazhuang area increased rapidly and recent figures show that it is more than 100 d-higher than in the Beijing area. Considering the impact of urbanization on dust-haze conditions and the fact that the extent of urbanization in the Beijing area is much larger than that in the Shijiazhuang area, this interesting initial find deserves further investigation.