So, carbon monoxide will kill you, obviously. But like a lot of things that will kill you, in small quantities it apparently makes you feel really great! In a recent study, carbon monoxide exposure made people less stressed out about the negative effects of living in the city, including crowds, noise, and presumably carbon monoxide exposure.
We're talking really low levels here — one to 15 parts per million — so don't go blowing out your pilot light. But that's the concentration of carbon monoxide that the researchers found participants inhaled on the streets of Tel Aviv, where the study was conducted. So it's realistic that city dwellers would be breathing this amount of CO on a regular basis. And this small, preliminary study does indicate a mild "narcotic effect" from the gas.
The study also found that noise pollution is the biggest contributor to stress in city-dwellers. A CO high helps you feel less edgy about the noise levels, but overall, quieting cities down might have a bigger effect on residents' health than cleaning up their air.
Is urban air pollution actually a stress-busting narcotic?, SmartPlanet.