Clean (and Dirty) Air Cities

There was a question recently about how to find a "clean air" city. With the world's population being over 50% urban, it's an important question. My quick answer is that it's difficult because even if you can afford to live away from coal plants, industry, oil refineries and fast food restaurants (they put out VOCs that cause pollution) and even highways, cars are just about everywhere and they are emitting pollutants into the air.

A study just came out in Environmental Science, however, on greenhouse gas emissions by city. This does and doesn't correlate to clean air, which is also dependent on a host of other factors (non ghg pollutants, air movement, etc.) but it is still enlightening.

The study looked at ten cities; Bangkok, Barcelona, Capetown, Denver, Geneva, London, Los Angeles, New York, Prague and Toronto. The amount of GHG emissions from a city has a lot to do with population density, energy sourcing, industry and transportation, but public and political will is most certainly also a factor.

Denver emitted far more emissions than any other city due in large part to emissions from ground transportation and electricity use. Los Angeles came in second, followed closely by Cape Town and Toronto. Then comes Bangkok and New York followed by Prague and London.

The city with the least GHG emissions? Barcelona by a long shot. The second lowest is Geneva (so Denver can't use cold weather as its excuse).  

So while there are lots of factors in finding a "clean air" city, emissions profiles are certainly one of them.