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 Oregon Department of Environmental Quality

Air Quality

Air Pollution Advisories

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Why the AQI Would Indicate Good Air Quality Even During a Smog Advisory

Ozone pollution builds up over the course of a hot sunny day and reaches it's peak in the late afternoon and early evening. The AQI reflects an average of the previous 8 hours of ozone pollution. For instance at 4 p.m. the AQI is an average of the 8 previous hourly readings (8 a.m. to 4 p.m.). That includes the period of time when ozone levels are at their lowest (in the morning).

The eight highest hours usually occur between 1 p.m. and 9 p.m. when temperatures are highest. The formation of ground-level ozone (smog) takes time. Ozone is formed when pollutants from cars, industry, other gas engines (lawnmowers, boats) and products we use every day (personal care items, spray cans, paint) react with oxygen in the presence of sunlight, particularly when it's hot.

Image of 8 hour ozone average chart
[print version]

 

For more information about Air Quality call 503-229-5359 or email.

Oregon Department of Environmental Quality
Headquarters: 811 SW Sixth Ave., Portland, OR 97204-1390
Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

The Oregon Department of Environmental Quality is a regulatory agency authorized to protect Oregon's environment by
the State of Oregon and the Environmental Protection Agency.

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