edunlea’s Recent Comments

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  watch your neck

  The most efficient thing I've found to help keep me warm is a neck gaiter.  Anything to keep the neck warm really helps, so I suppose a scarf would work too, but I'm not that stylish :)

  Also, I have not found much use myself for fancy tires, I think the biggest thing on ice is just staying balanced and going slowly... sometimes, really, really slowly.On Umbra on winter biking posted 1 year ago 18 Responses

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  winter vs summer pollution

  As an atmospheric chemist (and avid bicycle commuter), I thought I would pipe in here quickly.  In general, pollution can be classified as one of two types: primary or secondary.  Primary pollutants are those emitted directly into the air - carbon monoxide, sulfur dioxide and nitrogen oxides are good examples.  Secondary pollutants are those that are formed by chemical reactions in the atmosphere that are largely driven by sunlight - ozone is the best example of this.  

  In the winter, sunlight is weaker, which does two things: One, as Umbra so nicely explains, this inversion layer that forms (referred to as the "boundary layer") is lower to the ground meaning that pollution is mixing into a smaller box; this means primary pollutant concentrations are generally higher.  Two, the sunlight-driven chemistry of the atmosphere is slower, making secondary pollutants relatively lower.

  In the summer, the opposite happens - primary pollutants are relatively lower because they mix into a larger volume (higher boundary layer), but secondary pollutants are relatively higher because the sun is cooking things more intensly.  This is why you generally get poor air quality warnings during the summer (high ozone levels), but you see (and if you are riding a bike, often taste) the pollution during the winter (high carbon monoxide and some particulate matter - see next paragraph).  

  Interestingly, particulate matter, which you will often hear as "PM", has both primary and secondary sources.  The stuff that you see coming out of a diesel truck for example is primary PM.  Secondary PM is the stuff that you can't see, and this is generally the stuff that is more detrimental to human health because it is generally smaller and thus penetrates into the lungs further.

  There are of course lots of complicating factors to this whole picture, including emission patterns, which Umbra and others discuss above.  But, in general, some pollution gets relatively worse in winter (primary) and some gets relatively worse in summer (secondary), but none of it is fun to ride a bike through.On Umbra on air quality and temperature posted 2 years, 9 months ago 11 Responses