Air pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m, μg/m, etc.) at sea level will decrease with increasing altitude. The concentration decrease is directly proportional to the pressure decrease with increasing altitude. Some governmental regulatory jurisdictions require industrial sources of air pollution to comply with sea level standards corrected for altitude. In other words, industrial air pollution sources located at altitudes well above sea level must comply with significantly more stringent air quality standards than sources located at sea level (since it is more difficult to comply with lower standards). For example, New Mexico's Department of the Environment has a regulation with such a requirement.
The change of atmospheric pressure with altitude (<20 km) can be obtained from this equation:
Given an air pollutant concentration at sea-level atmospheric pressure, the concentration at higher altitudes can be obtained from this equation:
As an example, given an air pollutant concentration of 260 mg/m at sea level, calculate the equivalent pollutant concentration at an altitude of 2800 meters:
:C = 260 × [ { 288 - (6.5)(2.8) } / 288] = 260 × 0.71 = 185 mg/m
Note:
* The above equation for the decrease of air pollution concentrations with increasing altitude is applicable only for about the first 10 km of altitude in the troposphere (the lowest atmospheric layer) and is estimated to have a maximum error of about 3 percent. However, 10 km of altitude is sufficient for most purposes involving air pollutant concentrations.