Air pollution from vehicles, industry and the burning of plant material can choke off the formation of precipitation in some semi-arid mountainous areas, threatening critical water sources, a new study finds. Aerosols, or tiny particles suspended in the air, could potentially affect the climate by reflecting light back to space and therefore cooling the surface below or altering the formation process of clouds and precipitation. Because aerosol measurements have only been collected reliably more recently, scientists have been unable to conclusively demonstrate the effects of aerosols on precipitation, but this new study did just that using meteorological data extending back to the 1950s and collected on a mountain in central China. How it works Clouds form over mountains when air is pushed upward against one side of the mountain and subsequently cools, causing the water vapor in it to condense. As the air descends on the other side of the mountain, it warms and the clouds evaporate. Water vapor forms cloud droplets by condensing onto aerosols. These droplets collide until they form large droplets and eventually become heavy enough to fall as rain. Because there is only a certain amount of water vapor in the […]