Bad Air days and Bicycling
|
Submitted by jcock on Fri, 07/01/2005 - 06:59.
General Topics
Good info from a recent listserv discussion. . .
Yes, the Toronto study that Norma referenced states The mean hourly PPB figures quoted in Table 4 indicate that ozone levels on "main streets" and "major arterials" are approximately two thirds of the levels on "residential streets." It's ironic that the nitrogen oxides (NO and NO2) emitted by motor vehicles react with volatile organic compounds (also emitted) in the presence of sunlight to form ozone, yet if ozone is already present, one of the nitrogen oxides, nitric oxide, reacts with it to destroy it (presumably, the reaction is NO+O3-->NO2+O2). The potential to form ozone still exists, because the NO2 can drift off to participate in an ozone producing reaction, but the ozone in the "high traffic area" itself is reduced. Warnings of "bad air days" may give the public the false impression that there is zero risk on other days. In reality, of course, ozone levels fluctuate and there is always some ozone present; any level which triggers an alert must be somewhat arbitrary. Those who would consider substituting bicycle trips for car trips are people who will probably make the trips anyway, and if they travel by car the emissions will include nitrogen oxides that contribute to production of more ozone. Health Canada notes (http://www.hc-sc.gc.ca/english/iyh/environment/road_traffic.html) that use of transit and walking can also help reduce traffic-related air pollution. Neither of these would involve as much exercise as cycling, but the Toronto study cautions that
A study of adult hikers found that with prolonged hiking in an outdoor setting, exposure to ozone, PM2.5 and acid aerosols was associated with significant impacts on pulmonary function. Thus, the best option for avoiding ozone on a "bad air day" might be to use transit as much as possible (and walking for the remainder) to accomplish one's trips. It should be kept in mind that Air Quality Index levels are calculated from the readings of monitors at discrete locations. If one's trip route is mostly on major arterials (with, one hopes, bike lanes or wide curb lanes), ozone levels to which one would be exposed may be only two thirds of what they are in residential neighborhoods, according to the result quoted above. One could actually have significantly less ozone exposure by taking the trip by bicycle than if one drove to a nearby gym and spent the same amount of time (as the deferred trip travel would have taken) riding a stationary bicycle. Dwight Kingsbury |