Friday, March 5, 2010 2:40 PM CST
An air-quality advisory has been issued for Cerro Gordo, Worth and Butler counties, according to the Iowa Department of Natural Resrouces.
Fine particulate levels near EPA health standards are expected to persist in these areas until noon Saturday.
The DNR recommends that individuals with respiratory or heart disease prolong exertion until air quality improves.
The elderly and children also are advised to limit prolonged outdoor exertion.
The Environmental Protection Agency’s 24-hour health threshold for fine particles is 35 micrograms per cubic meter. As of noon Friday, fine particle levels averaged in the high 30s to low 40s across parts of northeast Iowa.
Fine particles are emitted by vehicle traffic and other combustion sources, and are formed by chemical reactions in the atmosphere. Stagnant air masses do not allow the fine particles to disperse, and pollutant levels rise.
The fine particle levels in the state have been following a pattern of rising rapidly during the evening and nighttime hours, and falling back to levels below the standard in late morning or early afternoon. This cycle is expected to continue until winds pick up Saturday afternoon.
EPA’s national air quality map is available online at www.airnow.gov.