Which is Better, Indoor or Outdoor Air?

Jul 30, 2010

If you do a quick straw poll on this questions, the results will be mixed. Some point to vehicle exhaust and factories and say the indoor air is better. Others point to volatile organic compounds (VOCs) and airborne microorganisms indoors, and say the outdoor air is better.

This morning I was reading the August edition of the journal, Indoor Air. The editorial by William Nazaroff raised this very question about indoor vs. outdoor air.

The answer to this question has wide implications. If the outdoor air is of a better quality than the indoor air, then we want to promote ventilation (bringing in outdoor air naturally or mechanically). If the indoor air is of a better quality, then we want to only bring in the bare minimum outdoor air as required by code.

When you look across the world, some cities and towns have better outdoor air, and others have better indoor air. But even that statement is an over simplification. We really need to look at individual contaminants. Let me explain by way of illustration…

Let’s say we have a home with elevated VOC levels due to some recent renovations. The home is in an area known to have elevated PM2.5 levels (particulate matter with aerodynamic diameter less than 2.5 microns). Let’s ask the question again… which is better, indoor air or outdoor air? They both have contaminants, so should we open the windows or keep them closed?

The overall answer to the question is the disappointing “it depends”. You will find contaminants in both indoors and out, so “pick your poison”. Before you purchase the next ticket to the moon to escape all these contaminants, let me give you some parting advice:

To reduce indoor contaminants, identify the sources and control them. Why were there elevated VOCs from renovations in our example? Use low-VOC products that are now readily available.

To reduce outdoor contaminants, bring in ventilation through the heating and cooling (HVAC) system. By installing good filtration on the system you will be able to clean and condition the outdoor air before it is supplied to the space. If you are not sure what the outdoor air quality is like in your area, visit this page: EPA AirData.

If you have some thoughts on the quality of indoor vs. outdoor air, please add a comment below!