Outdoor traffic sources?

How much do outdoor automobile traffic tailpipe emissions affect me indoors?

Look toward where the slow, stagnant air comes from, which in Seattle and Puget Sound is the NW, or in Salem is N (vs. prevailing winds from the SW on clean air days):  Do you see a busy stop-light or stop-sign intersection nearby with a lot of dirty emissions from cars stopping and starting?  or climbing uphill?  That will probably be more important than freeway traffic moving freely.

How bad is a freeway nearby?

  • Freeway traffic adds to all the other street traffic emissions the clean air picks up heading towards you.  But even 4 lanes of stalled freeway would be just like another 4 lanes of stalled arterials.
  • You can rely on the above arguments to help you put the freeway in perspective.  Or you can possibly test outdoors, as follows:

How can we test outdoors for auto emissions?

  • Test most easily for carbon monoxide (CO) using a continuous monitor to map the plume.
  • Testing for VOCs is not so easy or specific to traffic.
  • Testing for suspended fine soot particles (particulate matter) mainly from fuel combustion byproducts is somewhat specific, but they also come from other combustion sources.  This is more complicated and expensive.

How would we test outdoors for auto emissions

  • Test on a worst-case still-air day.
  • Start testing where you are located.
  • Then test while moving upwind.
  • Monitor continuously from you to past traffic, where the concentration should go to below 1 ppm.
  • Go over and past the freeway to show how big a contribution it might be.


I suggest you rely on good indoor air filtration for particles, plus charcoal for VOCs.