80 km-radius 2007 area, above Hohhot, capital city of north China's Inner Mongolia Autonomous Region Hebei Province, 1990 - 2002; 100,000 km e.g. 180 days from Mar - Oct in 2002 Hubei Province, 1996 - 1999 2,500 km every year; e.g. target area Jun - Sep in 1999 10,000 km target area, Shaanxi Province