Air pollution is turning China dry
June 20, 2006
BELCHING chimneys and cars in China are making the skies dry up. Smoke particles are changing the behaviour of the atmosphere and preventing raindrops from forming.
Chunsheng Zhao from Peking University in Beijing and his colleagues studied 40 years' worth of rainfall records along with six years' satellite measurements of aerosol particles. Between 1961 and 2000 they saw a decrease in rainfall of up to 0.4 per cent per year over eastern central China. The six years for which there is satellite data show a strong correlation between the lower rainfall and an increase in aerosol particles (Geophysical Research Letters, DOI: 10.1029/2006GL025959).
The increase in pollution affects rainfall in two ways. First, extra particles increase the number of tiny cloud droplets, but these repel each other, discouraging the formation of the heavy droplets needed for rain. Second, black sooty particles absorb sunlight, raising the temperature in the upper atmosphere. This reduces the amount of mixing with the lower atmosphere, which decreases the likelihood of clouds forming.
Already the region has been feeling the impact of reduced rainfall, and the situation for agriculture looks set to get worse. "Clean air action is urgently needed," Zhao says.
