The use of proportion varies in air quality regulations depending on the specific pollutant being regulated and the associated health risks. For example, the Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS) for certain pollutants, such as ozone, based on a proportional approach that considers the percentage of the pollutant in the air and the associated health risks at different concentrations.
In contrast, for other pollutants, such as particulate matter, the EPA takes a more absolute approach that sets a fixed standard for the maximum amount of the pollutant allowed in the air as measured by mass per volume.
Additionally, the use of proportion may vary depending on the range of concentrations at which a pollutant poses health risks. Some pollutants may have a linear relationship between concentration and health risks, while others may have a threshold below which there are no measurable health risks. In these cases, the use of proportion may be different in determining appropriate regulations and standards.
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