Image by kqedquest via FlickrThe garage as far as we are concerned is one of the most dangerous areas of the home.  Between the car, tool, and chemical storage it can have various items that by themselves would have significant impacts on indoor air quality.  Individually, cars can impact air quality with the carbon monoxide they produce that can infiltrate the home, tools, depending on what powers them, can also have the same effect as a car or can generate contaminants like sawdust, silica, asbestos or other hazardous vapors, and chemical storage by itself can generate volatile organic compounds (VOCs) and other hazardous vapors and mists.   The above article points out various ways you can improve your air quality and the ideas are excellent.