Every fall around this time of year the temperature inversions start outdoors. Basically, the inversion is a layer of separating warm and cold air that traps particulate and keeps it close to the ground (this is what causes the noticible "brown haze" that you see driving into many Southwest cities such as Phoenix or Tucson). Here is a good article from the Tucson paper talking about the outdoor air quality http://www.azstarnet.com/metro/266628.php .
While you are at it, check out our blog entry from earlier this year that talks about the relationship between indoor and outdoor air quality http://www.merchantcircle.com/blogs/DUCTZ.Indoor.Air.Professionals.623-466-8625/2008/3/Outdoor-air-mess-means-indoor-air-nightmare-/72419 .
DUCTZ of North Phoenix and Deer Valley is licensed by the Registrar of Contractors to clean residential and commercial duct work in the State of Arizona. In addition, we are members in good standing with the Better Business Bureau (BBB) and certified by NADCA (National Air Duct Cleaners Association).