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February 24, 2010 2:45 AM   Subscribe

How can I weigh the exercise benefits gained from walking against the damage caused by breathing exhaust? I like walking along busy city streets for miles, and I don't want to switch to quieter/duller residential roads, but I'm wondering if I should.

Let's say I walk for 1 to 3 hours, four times a week, along wide streets (with several lanes) in Los Angeles. There's evidence that lots of walking is good for your health, and there's evidence that lots of pollution is bad for your health. What research I can compare to estimate whether this is doing more harm than good, and whether walking on less-trafficked roads would make a significant difference? (If it matters, I'm generally healthy.)

A few articles I found:

* Comparison of air pollution exposure for five commuting modes in Sydney and Personal Exposures to Traffic-Related Air Pollution while Walking and in the Car -- suggest that all forms of transportation involve inhaling lots of pollution, more of it the longer you're outside.

* Pedestrian exposure to air pollution along a major road in Central London and Ultrafine Particle Deposition in Humans During Rest and Exercise -- both provide measurements without saying whether those levels are harmful.

* Exercise and outdoor ambient air pollution and Comparative respiratory effects of ozone and ambient oxidant pollution exposure during heavy exercise -- both note short-term negative effects of pollution, but what about long-term effects?

* Exposure to hazardous volatile organic compounds [...] in urban Guangzhou and Beneficial cardiovascular effects of reducing exposure to particulate air pollution with a simple facemask -- pollution is definitely a problem for walkers in parts of China.

What else should I be looking at?
posted by dreamyshade to Health & Fitness (8 answers total) 5 users marked this as a favorite
The most recent Straight Dope column touched on this very subject. Unfortunately, Cecil didn't give any citations, but he notes that:
Ultrafine particles that primarily come from cars and trucks are especially problematic. Called PM2.5, meaning they're 2.5 micrometers (1/10,000th of an inch) or smaller, these particles can be inhaled deep into your lungs and stay there. Particulate pollution can trigger asthma attacks and allergies. Stress tests on both healthy men and those with mild heart disease show breathing diesel exhaust during exercise reduced blood flow to the heart and increased the risk of blood clots.
posted by Johnny Assay at 5:03 AM on February 24, 2010 [1 favorite]

I would weigh the benefits of walking against the risk of being struck by a motor vehicle given the area you are getting your exercise in. That's a much more dire risk than a slight increase in inhaled air pollution.
posted by Modus Pwnens at 5:06 AM on February 24, 2010

Something else: what's to say those side streets actually have less pollution? Air quality is a systemic problem in Los Angeles, and moving one or two blocks off the main drag does not guarantee a dramatic improvement in air quality, especially since some of the most common pollutants, like ozone, are odorless and colorless.
posted by valkyryn at 5:36 AM on February 24, 2010 [1 favorite]

You could wear a dust mask, like the disposable kind you find in the paint section of hardware stores. ...You might look like a weirdo, but hey, Los Angeles. ;-)
posted by applemeat at 6:18 AM on February 24, 2010 [1 favorite]

If you want to go all-out, there are masks available that claim to filter out "urban pollutants" - here and here are two examples.
posted by purlgurly at 7:22 AM on February 24, 2010

Best answer: What time of day do you tend to walk? The general wisdom according to fitness magazines (although I couldn't find a cite to an actual study) is that air quality is best in the early morning. Air quality also varies throughout the year and can be especially bad in hot summer months. If you're in the US, you can check daily air quality readings at airnow.gov. Maybe you can mitigate possible effects by walking in the early morning and avoiding high-ozone days.
posted by messica at 8:16 AM on February 24, 2010

Just a data point: I walk every day in a small Northern California beach town. For some reason, my part of the world is populated, dare I say overpopulated with diesel trucks. It seems as if every third person drives one. It may have something to do with their imagined shortcomings elsewhere; I don't know. The point is that I have to breathe their exhaust every time they pass me and it's really, really annoying. I, too, have had concerns about the micro-particulants, as I have asthma. However, I keep walking because most of the time on my walks, I have fresh ocean air to breathe and am hoping it pushes out all the bad stuff.
posted by Lynsey at 9:57 AM on February 24, 2010

Response by poster: Hmmm, thanks everyone! For myself, I think I'm less concerned about asthma and allergies and more concerned about increasing my risk for heart disease and cancer (another thing I just found: "Los Angeles residents living near freeways experience a hardening of the arteries that leads to heart disease and strokes at twice the rate of those who live farther away"). Of course, reduced lung capacity in any form isn't great, but my family has a history of cancer and I probably should be especially careful not to taunt it.

Yeah, diesel exhaust is terrible — when I smell it, I try to breathe inside my shirt as a type of filter. (And a favorite the other day was a small truck hauling a vat of hot smelly tar...) But I already wear a goofy wide-brimmed hat on sunny days, so I'm not sure I want to add a dust mask to my ensemble, even if it's a good idea. :)

And I agree, it's good to consider my other risks — a vehicle runs into a storefront every couple years around here, but people sometimes get robbed etc. on quiet side streets, so I figure that's something of a toss-up.

I usually walk during the afternoon, but walking in the morning seems to make sense for less particulate matter in the air. I'll do that more often. The link to airnow.gov is helpful too. Thanks again!
posted by dreamyshade at 3:19 PM on February 24, 2010

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