Correcting concentrations for altitude

Correcting concentrations for altitude

Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m³, µg/m³, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude.
The change of atmospheric pressure with altitude can be obtained from this equation:^[2]

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Given an atmospheric pollutant concentration at an atmospheric pressure of 1 atmosphere (i.e., at sea level altitude), the concentration at other altitudes can be obtained from this equation:

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where:
Image may be NSFW. Clik here to view.	= altitude, in hundreds of meters
Image may be NSFW. Clik here to view.	= atmospheric pressure at altitude Image may be NSFW. Clik here to view., in atmospheres
Image may be NSFW. Clik here to view.	= Concentration at sea level altitude, in mass per unit volume
Image may be NSFW. Clik here to view.	= Concentration at altitude Image may be NSFW. Clik here to view., in mass per unit volume

As an example, given a concentration of 260 mg/m³ at sea level, calculate the equivalent concentration at an altitude of 1,800 meters:
C_a = 260 × 0.9877 ¹⁸ = 208 mg/m³ at 1,800 meters altitude