To the list of air pollution's health effects, add another one: loss of sense of smell. Mexico City residents can't detect subtle smells as well as residents of neighboring Tlaxcala, researchers at Mexico's National University (UNAM) have reported, though the regions are quite similar in both culture and climate. The primary difference: Mexico City has much higher levels of air pollution.

EMBARQ, the WRI Center for Sustainable Transport, recently traveled to Mexico City to report on this phenomenon.

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Globally, the two air pollutants that present the biggest health problems are ozone and particulate matter such as dust, smoke, or haze. Well-studied health effects of both include respiratory irritation, difficulty breathing, and reduced lung function.

But this new research demonstrates that there are some effects of air pollution still unknown to us, only revealed as pollution reaches ever higher levels. 'We're only picking up these problems in recent years,' says Robyn Hudson, a biomedical researcher at UNAM. So the long-term effects of this quantity of pollution will likely be more serious than any we've yet seen.