Pima County officials are investigating whether mine tailings played a role in the county topping federal air-quality standards for the first time since 2009 during high winds last week.
According to the Arizona Daily Star, levels of large dust particles at a monitor in the Green Valley area were nearly three times the federal limit on April 9.
The limit also was exceeded by dust levels the same day in Tucson and on both April 8 and 9 in South Tucson.
According to county officials, construction sites are among potential sources of the dust along with Asarco and Freeport McMorRan copper mines near Green Valley and Sahuarita.
Company officials say some tailings blew from their sites but the high dust levels also came from other sources.
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