Air pollution extends 1.5 miles from major roads and is worse before sunrise.

An environmental health research team from UCLA, the University of Southern California and the California Air Resources Board, headed by Dr. Arthur Winer, a professor of environmental health sciences at the UCLA School of Public Health, found that during the hours before sunrise, air pollutants from Interstate 10 in Santa Monica extend as far as 2,500 meters — more than 1.5 miles. This is 10 times further than previously measured duringthe day time and has significant exposure implications, since most people are in their homes during the hours before sunrise and outdoor pollutants penetrate into indoor environments.

To measure the pollution levels, they equipped an electric vehicle with no emissions of its own with fast-response instruments for gaseous and particulate air pollutants, a GPS and video monitor, and instruments to measure temperature and winds. In both the winter and summer of 2008, they drove toward and away from Interstate 10 on a route perpendicular to the freeway in Santa Monica between the hours of 4 a.m. and 7 a.m"

A second striking finding of the study was that although traffic volumes are lower in the pre-sunrise hours, the air pollution concentrations were higher than even those during daytime traffic congestion peaks. Concentrations are higher before sunrise even though emissions are lower because, 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.

This means that areas south of Interstate 10 are generally downwind in the pre-sunrise hours and areas north of the freeway are generally upwind; this is consistent with the observation that vehicle-related pollutants are found much further from the freeway on the south side in the pre-sunrise hours, compared with the north side.

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.

In comparing the winter and summer early mornings, researchers found much higher levels of air pollution in the winter because the sun rises later in the winter, so the early morning period captures more of the early morning rush hour.

Elevated pollution, including nitric oxide and particle-bound polycyclic aromatic hydrocarbons, also extended up to 600 meters upwind of the freeway, another strong difference from daytime observations, which typically show little or no vehicle-related pollution directly upwind from freeways.

Numerous epidemiologic studies have already shown that traffic-related pollution is linked to increased risk of asthma, respiratory illness, cardiovascular disease and premature mortality.
The researchers recommend that residents living near freeways should consider keeping their windows closed at night and minimise outdoor exercise near major roadways in the hours before sunrise.

Atmospheric Environment

Read more

Click here for more research on asthma

First Published in June 2009


Top of page