Because of unusually high late-season temperatures and stagnant atmospheric conditions, valley air officials have declared the year's second air alert.
The air alert began Saturday and is expected to continue through Wednesday. Alerts are declared Valleywide when environmental conditions are likely to trigger violations of the federal one-hour ozone standard.
Ozone is created when high temperatures heat up a mixture of nitrogen oxide, or NOx, which is a fuel-burning emission, and volatile organic compounds, or VOCs, such as emissions from aerosol cans and waste from dairy cows.
The temperature for Merced over the next few days is expected to reach triple digits and could break records.
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On Monday, the high hit 99 degrees, tying the record for that date set in 1952, according to Accuweather.com. It's not expected to cool down until Thursday, when the high is forecast to be 90 degrees.
"Any help from the public is greatly needed," said Anthony Presto, spokesman for the San Joaquin Valley Air Pollution Control District. "The main thing we need residents to do is look at their daily activities that impact air quality."
Valley residents are asked to reduce unnecessary driving time and idling, as well as refrain from use of gasoline-powered equipment such as lawnmowers. Barbecuing is also highly discouraged.
"Normally, when we get to October, our ozone is not the dominant pollutant," Presto said. "As the days get shorter and cooler, ground-level ozone decreases. That's why this is an unusual event."
The earth's ozone layer protects people from ultraviolet rays from the sun, but ground-level ozone is a corrosive gas that damages lung tissue and has been linked to cancer, asthma, emphysema and other health concerns.
Because of the Valley's dangerously unhealthy air conditions, the U.S. Environmental Protection Agency has levied a $29 million annual fine on residents. The money, collected through a vehicle registration fee, has been used by the regional air district to implement air-quality improvement efforts.
To meet EPA standards and get out from under the fine, the Valley has to register three years in a row in which the one-hour ozone standard is not violated at any one monitoring location more than three times.
The Valley is working on completing year one, with no violations recorded in August or September. However, this year there have been 91 ozone violations, including two at a location in Fresno.
Reporter Joshua Emerson Smith can be reached at (209) 385-2486 or firstname.lastname@example.org.