Urban Air Pollution: Stay on the Windy Side of the Street

Thinking of an urban stroll to clear the head, move those bones, and take in a breath of fresh air? Be careful that noxious car exhaust doesn’t put a dent in your healthy walk. A new study helps point the way.

We’ve made a lot of progress cleaning up the air in our cities, but we have a long way to go.

A case in point, the Environmental Protection Agency just released its latest list of non-attainment areas for fine particle pollution: 120 areas in 31 different counties of 18 states do not meet safety standards for this pollution that's so tiny (some ten times smaller than the width of a human hair) that it can pass through the body’s protective cells into the heart and lungs and can lead to serious health problems such as an asthma attack, the development of chronic bronchitis, and possibly even a heart attack.

Cars and Trucks Belch Toxic Pollutants

Not surprisingly, a number of major metropolitan areas are on EPA's new list. A major culprit is the pollution that comes from so-called mobile or traffic-related emissions.

Cars and trucks spew a huge array of pollutants into the atmosphere, including, in addition to fine particles, hydrocarbons, nitrogen oxides, carbon monoxide (CO), and air toxics.

I suspect all of you, if given the choice, would prefer not to inhale any of it. But how to avoid it? Alison Tomlin at the University of Leeds and her colleagues provide some answers in their research into the complex dynamics between airflow, traffic flow, and street geometries.

Aiming to get a better handle on how and where people are exposed to traffic-related air pollution, their most recent work, described in a paper just out in Atmospheric Environment, gives the lowdown on how carbon monoxide (CO) concentrations varied at and near a busy intersection of two canyon-like streets in London. Because emissions from cars and trucks are the dominant source of CO in the urban environment, CO concentrations provide a good proxy for the presence of traffic-related pollution.

Pollution from Traffic Is 'Hottest' Closest to the Source

While there are many variables that impacted the variations of CO they recorded, the authors were able to tease out three conclusions that you may want to bear in mind the next time you head out on foot in a city:

• As you might expect, the highest levels of air pollution were measured near the intersection itself.
• Away from the intersection, higher levels of CO tended to concentrate on the leeward or sheltered side of the streets.
• During times of peak traffic flow, CO concentrations on smaller side streets were approximately four times lower than those at the intersection and along the main streets.

So, folks, I suggest turning up your coat collar and pulling down your hat before heading into the wind this winter. Also, you might want to take to the windy sides of those urban canyons, a choice that may just be good for your health. Or, even better, avoid the main thoroughfares altogether, and head for a quaint little side street.