Concern about indoor air quality (IAQ) and the study of air quality issues is a fairly recent
phenomenon. Some of the earliest documented studies occurred in Scandinavia in the mid-1960s
and were focused primarily on thermal comfort issues. For the first decade or so, IAQ studies
primarily involved comparing indoor air to outdoor air. The level of outdoor pollution was a chief
concern and the goal was to ensure that indoor air was of better quality than the outdoor air
subjected to pollutants.