Amongst air pollution specialists, it's been common knowledge that the worst potential health impacts from freeway air pollution extend 500 yards or three football fields from freeways and major roadways.
But according to a new study published last month in the journal Atmospheric Environment, freeway air pollution extends as much as 1 and 1/2 miles downwind, impacting people in many more homes, as outdoor air pollutants penetrate indoor environments through cracks in windows and doors.
Environmental health researchers from UCLA, including lead author Dr. Shishan Hu, from the UCLA School of Public
Health, and scientists at the University of
Southern California and the California Air Resources Board found
that during the hours before sunrise, freeway air pollution extends
much further than previously thought.
The research team headed by Dr. Arthur Winer, professor of environmental health sciences at UCLA took recent air pollutants measurements from Interstate 10 in Santa Monica, which extended as far as
2,500 meters — more than 1.5 miles — downwind. This distance is 10 times greater than previously measured
daytime pollutant impacts from roadways and has significant exposure
implications, since most people are in their homes during the hours
before sunrise.
"Our research shows that under the low wind speeds and shallow
temperature inversions during the early morning, before sunrise, air
pollution from freeways is trapped near the surface, limiting dilution
and creating a zone of influence many times greater than during the
day," said Dr. Suzanne Paulson, a professor in the UCLA Department
of Atmospheric and Oceanic Sciences and a co-principal investigator of
the study. "These meteorological conditions are very common in the
hours before sunrise."
Although traffic
volumes are lower in the pre-sunrise hours, the air pollution
concentrations were higher than those during
daytime traffic congestion peaks because of the unique weather
conditions. In the pre-sunrise hours, wind speeds are generally very
low, and while the wind direction is somewhat variable, the predominant
direction is from the northeast in the winter months and the northwest
in the summer months.
In comparing the winter and summer early mornings, researchers found much higher levels of air pollution in the winter.
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