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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Air Actions, Ajo, AZ

Air Actions in Ajo, Arizona

January 24, 2006: Particulate Matter in Ajo, Arizona

EPA has signed a direct final rule determining based on ambient monitoring data that the Ajo area in Arizona has attained the short-term (24-hour) and long-term (annual) primary National Ambient Air Quality Standards (NAAQS) for particulate matter (PM-10). The Ajo area has not had an exceedance of either the annual or the 24-hour health-based standard since 1987. The Act and our regulations require three years of clean data to make this finding. Once this clean data finding is effective, the State will be relieved of certain attainment, reasonable further progress, and related requirements so long as the ambient air quality standard continues to be met. Our action will streamline the process for the Arizona Department of Environmental Quality (ADEQ) to request redesignation of this area to attainment. The primary sources of PM-10 pollution in the Ajo include tailings piles (waste left from various milling, mining, and distilling processes at the Phelps-Dodge New Cornelia mine and smelter), vehicular traffic on Highway 85, unpaved roads, and cleared areas. The mine and smelter ceased operation in 1985 and the smelter was dismantled in 1995 and 1996.

Related Documents

Direct Final Federal Register Notice

Federal Register proposal

Media Advisory

(January 27, 2006) Ajo, Ariz. meets federal air quality standard for PM-10

SAN FRANCISCO – The U.S. Environmental Protection Agency today announced that the Ajo, Ariz. area has met the federal health standard for particulate matter pollution. Sources of PM-10 emissions in Ajo, located in western Pima County, include waste left from various milling, mining, and distilling processes at the New Cornelia mine, vehicular traffic on Hwy 85, unpaved roads, and cleared areas. The last time the Ajo area exceeded the PM-10 federal air quality standards occurred in 1987. Ajo is one of several early settlements in Arizona where mining and copper smelting were prominent. When the New Cornelia mine, operated by Phelps Dodge, closed in 1985, the population of the Ajo area significantly declined. PM-10 causes adverse health effects by penetrating deep in the lungs, aggravating the cardio-pulmonary system. Children, the elderly, and people with asthma and heart conditions are the most vulnerable.

Contact Information

Wienke Tax (tax.wienke@epa.gov)
Office of Air Planning
EPA Region 9
(520) 622-1622


September 25, 2003: Approval of Arizona's Plan to Meet the Sulfur Dioxide Air Quality Standards in the Ajo Area

EPA has approved Arizona's maintenance plan to maintain attainment of the short-term (24-hour) and long-term (annual) primary National Ambient Air Quality Standards (NAAQS) for sulfur dioxide (SO2) in the Ajo area, as well as Arizona’s request to redesignate this area from nonattainment to attainment for SO2.

The Ajo area has not had a violation of either the annual or the 24-hour health-based standard since 1980. The primary source of sulfur dioxide pollution in the Ajo was the Phelps Dodge Ajo Incorporated smelter, which ceased operation in 1985 and was dismantled in 1995 and 1996. There are currently no other SO2 sources of this magnitude in Ajo.

Related Documents

Contact Information

Wienke Tax (tax.wienke@epa.gov)
Office of Air Planning
EPA Region 9
(520) 622-1622

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