These days we hear a lot about how air pollution is changing temperatures on the earth. New evidence from a mountaintop in China now suggests that pollution can also change the amount of rain and snow that falls in some places. Usually, more rain falls in mountainous places than in flat areas upwind from the mountains. That's because air can hold a lot of water. When wind blows wet air up a mountainside, the air gets colder. This temperature change often forces water to fall as rain or snow. In recent years, however, many mountainous areas in the western United States have been getting less rain than normal. Mountains that are downwind from cities have experienced the biggest drops. Some scientists have theorized that pollution drifts  from the cities into the mountains, affecting rainfall, but proving this link has been difficult. Searching for answers, a team led by a scientist from the Hebrew University went to s mountain in China called Mount Hua, which is 2,060 meters tall and lies about 120 kilometers east of the Chinese city Xi'an. Since 1954, scientists have been collecting details about rainfall, humidity , and visibility in the area. Using this data, the scientists compared rainfall on Mount Hua to rainfall in the nearest city, Huayin, on days with different levels of visibility. When the air was clear and people could see as far as 20 km, the scientists found that 65% more rain fell on the mountain than in the city. But when the air was smoggy, allowing only 8 km of visibility through the mist, the mountain received just 20% more rain than the city. The new data supports the theory that pollution affects rainfall. Some scientists believe that there are other explanations for the numbers. It's possible, for example, that natural particles in the air, rather than particles produced by pollution, are affecting visibility. You can most probably read the passage in   _  .
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