The Diamond Complex fires east of Roseburg are among those creating smoky conditions in much of Oregon. (Photo by Northwest Interagency Coordination Center via Oregon Capital Chronicle)

Smoke and smog is clogging much of the air in Oregon, state officials said Wednesday.

At mid-day, the Oregon Department of Environmental Quality issued an air advisory for 20 of Oregon’s 36 counties due to wildfire smoke, then followed that up about 30 minutes later with a smog alert for the Portland area and Umatilla County.

The smog is caused by ozone pollution from the weather and traffic. Ozone forms when hot temperatures and low winds combine with pollution from cars, gas-powered engines and chemicals in paints and aerosols, the agencies said in a release. The pollutants react with sunlight and heat to produce ozone and haze.

Though the air quality can be clear in the morning, as the heat sets in and the hours tick by with the sun streaming down, pollution levels rise and tend to peak in the afternoon and early evening.

Smoke levels in the air can also vary during the day, depending on weather conditions. DEQ said that as dozens of large fires burn in Oregon, Washington and California that smoke-clogged air could plague Baker, eastern Benton, Clackamas, eastern Douglas, Harney, Hood River, Jackson, Jefferson, Josephine, central Lane, Linn, Malheur, Marion, Multnomah, eastern Polk, Umatilla, Wallowa, Wasco, eastern Washington and eastern Yamhill counties.

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Both smoke and smog irritate the eyes, nose and lungs and contribute to breathing problems. People who are pregnant, seniors and those with heart disease or respiratory conditions are especially vulnerable to smog. The agencies said they should avoid exposure, if possible, by limiting outdoor activities when pollution levels rise. 

The agencies advised people in the Portland area, where traffic can be heavy, and Umatilla County, with interstate and state and regional highways, to carpool or avoid traveling in a gas-powered vehicle altogether and use public transport to curtail the harmful emissions. They also said residents should avoid using gas-powered yard equipment, avoid letting vehicles idle and put off aerosol painting projects.

The smog advisory will remain in place in Umatilla County through 8 p.m. Wednesday and in the Portland area until 8 p.m. on Thursday. The smoke alert will run until Friday afternoon.

Lynne Terry has more than 30 years of journalism experience, including a recent stint as editor of The Lund Report, a highly regarded health news site. She reported on health and food safety in her 18 years at The Oregonian, was a senior producer at Oregon Public Broadcasting and Paris correspondent for National Public Radio for nine years. She has won state, regional and national awards, including a National Headliner Award for a long-term care facility story and a top award from the National Association of Health Care Journalists for an investigation into government failures to protect the public from repeated salmonella outbreaks. She loves to cook and entertain, speaks French and is learning Portuguese.