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Why Do Heat Waves Make Air Quality Worse?

Heat and sunlight make "chemical soup" that affects air quality

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Dear EarthTalk: Why does air quality get so bad during heat waves?
-- Chad Muller, Wellesley, Mass.

Air quality decreases during times of hot temperatures because the heat and sunlight essentially cook the air along with all the chemical compounds lingering within it. This chemical soup combines with the naturally occurring nitrogen oxide in the air, creating a “smog” of ground-level ozone gas.

This makes breathing difficult for those who already have respiratory ailments or heart problems and can also make healthy people more susceptible to respiratory infections.

Air Quality Worse in Urban Areas
According to the U.S. Environmental Protection Agency (EPA), urban areas are the most susceptible because of all the pollution being emitted from cars, trucks and buses. The burning of fossil fuels at power plants also emits a considerable amount of smog-making pollution.

Geography is also a factor. Broad industrialized valleys penned in by mountain ranges, such as the Los Angeles basin, tend to trap smog, making air quality poor and life miserable for those people working or playing outside on hot summer days.

Air Quality Far Exceeds Healthy Limits
The non-profit watchdog group Clean Air Watch reported that July’s intense heat wave caused a blanket of smog stretching from coast to coast. Some 38 U.S. states reported more unhealthy air days in July 2006 than during the same month the previous year.

And in some particularly at-risk locales, airborne smog levels exceeded the acceptable healthy air quality standard by as much as 1,000-fold.

What You Can Do to Improve Air Quality During a Heat Wave
In light of recent heat waves, the EPA urges urban dwellers and suburbanites to help reduce smog by:

  • Using public transit and carpooling to reduce vehicle trips
  • Refueling cars at night to prevent escaping gas vapors from getting cooked into smog by sunlight
  • Avoiding gas-powered lawn equipment
  • Setting air conditioning thermostats a few degrees higher to help reduce the fossil fuel burning needed to power them

How the EPA Plans to Improve Air Quality
For its part, the EPA is quick to point out that the regulations on power plants and car fuels that have been instituted over the last 25 years have significantly reduced smog in American cities. EPA spokesman John Millett says that “ozone pollution concentrations have declined about 20 percent since 1980.”

Millett adds that the agency is in the process of implementing new programs to control emissions from diesel trucks and farming equipment, and is requiring cleaner diesel fuel to help further reduce smog levels. New rules to regulate marine vessels and locomotives should also help minimize future smog alerts.

“Long-term we have made improvements … but this heat wave and the accompanying smog is a very graphic reminder that we still have a significant problem,” says Frank O’Donnell, Clean Air Watch’s president. “Unless we start getting serious about global warming, predicted increases in global temperatures could mean continued smog problems in the future. And that will mean more asthma attacks, disease and death.”

Protect Yourself from Poor Air Quality
People should avoid strenuous outdoor activity during heat waves in areas plagued by smog. For more information, check out the U.S. government’s Ozone and Your Health.

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EarthTalk is a regular feature of E/The Environmental Magazine. Selected EarthTalk columns are reprinted on About Environmental Issues by permission of the editors of E.

Note: For more information on how to protect yourself and your pets during a heat wave, see How to Avoid and Treat Heat Exhaustion and Heat Stroke.

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