Mexico City's notorious smog--for years blamed on automobile traffic and factories--is largely caused by millions of household fuel tanks for stoves and heaters that are leaking gases "on a massive scale," California scientists reported today.
Liquefied petroleum gas, Mexico's predominant fuel for cooking and heating, is "a large, previously unrecognized source" of the city's smog-causing fumes, according to UC Irvine's renowned atmospheric chemist F. Sherwood Rowland and senior research associate Donald Blake.
The leaking hydrocarbons mix with nitrogen oxides and react with sunlight to form ozone, the main pollutant that fouls the skies of Mexico City as well as the Los Angeles Basin.
Unburned gases such as butenes and propane that spew from the residential tanks "play a major (perhaps the dominant) role in ozone production in the valley of Mexico," the scientists reported in an article published today in the journal Science.
The researchers suspect that residential fuel might also be a key pollutant in other smoggy cities around the world, including Athens, Taipei, Taiwan; Santiago, Chile, and some U.S. cities. A notable exception is the Los Angeles Basin, where household fuel is a negligible source, and cars and trucks remain the major culprit.
In Mexico City, about 5 million households have rooftop canisters of liquefied petroleum gas, or LPG, and leaks are believed to be common during use and refilling, Rowland said.
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The findings could prompt Mexico to broaden its controversial strategy for battling smog in its capital city, where more than 15 million people are breathing severely polluted air that exceeds health standards on nearly a daily basis.
After meeting with the UC Irvine scientists, the Mexican government and petroleum industry recently began funding further research into the scope of pollution from LPG and ways to reduce it, Rowland said.
Mexico's environmental officials were not available for comment Thursday.
"Their procedures for trying to control smog have emphasized automobiles and industry, and that is clearly the right direction to go, but it should be expanded to include LPG," Rowland said in an interview Thursday. "They have a terrible smog problem, and I'm encouraged that they will try" to address the household pollution.
Mexico City's smog, which has grown dramatically over two decades, now mirrors the levels suffered in the Los Angeles area during the 1960s and 1970s.
