A Department of Natural Resources official says they’re still trying to determine what caused a bad patch of air near a Davenport foundry just over one week ago. Brian Button of the DNR’s air quality bureau says the dirty air was measured near the Black Hawk Foundry in southwest Davenport. He says it’ll take some time to find out what happened — if it was a problem at the foundry, or if winds pushed emissions down to the ground near the monitoring station. Button says we’re beyond the so-called smog season in Iowa. Button says smog is typically a summertime pollution, but he says particulate pollution, or small particles suspended in the air, can occur anytime of the year. You may see exhaust coming out of your home or your neighbors as the heater kicks in. Button says those emissions shouldn’t concern you. He says home heating doesn’t really pose too many problems for outdoor air as people are typically burning natural gas — which he says burns very clean. He says it used to be more of a problem when coal was burned for heat. Button says the fireplaces in most Iowa homes don’t pose a problem either. He says it’s more of a problem in western states where there are thermal inversions in the mountains that trap the emissions. Button says the smog season in Iowa usually ends in October and begins again in April.