It's Calming You Softly...with Its Smog
Noise is the biggest urban stressor, found a study at the Tel Aviv University. But one very weird thing appears to offset it: carbon monoxide from car exhaust. Even extremely low levels (approximately 1 to 15 parts per million every half-hour) of the odorless gas had a calming effect on volunteers, who were equipped with heart-rate and pollution monitors and kept track of their stress as they roamed the cityscape. In the loud zones, they felt more Zen when the pollution was higher than average. There were no lasting effects, bad or good. Obviously, this is no reason to sniff tailpipes. While a tiny amount may, strangely, relax us, carbon monoxide is a killer, resulting in about 500 accidental deaths a year.