Thursday, January 22, 2009

Winter Inversion Blues

Here in good ol' Salt Lake City, as well as other surrounding valleys in Northern Utah, we have been suffering from an inversion for a while now. I have received Red Air Quality alerts from the Department of Environmental Quality for the past seven days in a row. The air is soupy, and you can smell the muck and pollution in the air.

Photo Courtesy of Tom Smart, Deseret Morning News

The air quality system is based on red, yellow, and green burn days. Green means wood burning is allowed, yellow means a voluntary no burn, and a red light means no burning at all. You are also asked to drive as little as possible during yellow and red air quality days because cars contribute significantly to the area's air pollution. The health implications of Red Air Quality days are also significant. Health advisories go out saying that "sensitive people with respiratory disease or heart disease, the elderly, and children should avoid heavy or prolonged exertion. Everyone else should reduce heavy or prolonged exertion."

Does this sound really bad to anyone else? There are several areas in the state of Utah (Utah, Salt Lake, Davis, and Cache counties being some of them) that do not meet the current federal health standards for fine particulate (PM2.5) pollution, but it doesn't take a scientist with fancy recording tools to know that the air outside is unhealthy. Just take a look out your window, or go outside: it's pretty difficult to not notice the smell of the smoggy air. So what exactly is an inversion?

Several factors contribute to what are known as "surface inversions." Lower angles of sunlight that are present in the winter time do not heat up the earth's surface as well as they do in the summer. When the sun goes down, the air that is closest to the ground gets cooler than the air that is higher above the ground (which is opposite of normal air flows and weather conditions because generally the higher into the atmosphere air goes the colder it becomes, hence the name "inversion"). Since air is a poor conductor of heat, the air that is closer to the ground stays colder during the day time as the air that is further away warms with the rising of the sun. Also, since cold air is heavier than warm air, it stays down in the valley and the warm air floats on top, acting as a lid to the cold air. Then, in a valley that is surrounded my mountains like many of the valleys in Utah, air flow is prevented by the mountains and the hot air "lid" which traps not only cold air but also the pollutants that we emit.

Right now, an atmospheric high pressure is parked right over many of the Western states, including Utah. As long as this atmospheric high pressure is around, storms are thrust around the high pressure. Storms are useful for pushing out inversions as the air flow and wind that they bring with them disrupt the inversion and clean out the valley of the cold/warm air dichotomy as well as the trapped pollutants.

Surface inversions cannot be prevented, however the pollution that is trapped in them can be, or at least greatly reduced. Carpooling with coworkers, combining trips, avoiding unnecessary driving, and maintaining you vehicle are easy ways in which to reduce the pollution that is caused by cars, a major contributor to inversion pollution. For other ideas on how to improve air quality in both your car and other ways, check out the Utah DAQ webpage.

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