Emissions of air pollutants and air quality are related to each other, but not in a one-to-one relationship. Some places are very sensitive to air quality problems because of local weather patterns and topography (e.g. the Los Angeles region). In other areas weather and topography combine to make the region relatively insensitive to air quality problems. In some cases a large portion of a country’s air pollutant emissions travel into neighboring countries before they react with the atmosphere to degrade air quality. Conversely, a country may import a large amount of pollution from its neighbors, and its air quality may suffer even if its emissions may be relatively low.

Also, there is no international standard for where air quality monitoring sensors should be placed. Thus, in one country they may be in close proximity to polluting industries or major motorways whereas in another they may be far removed from such locations.