Posted Mon, 08/31/2009 - 21:06 by andrzejc

How we calculate the relative toxicity of pollutants

Relative toxicity of various pollutants is not easily determined. However, there exists already a body of work on this subject, performed by the US Environmental Protection Agency (EPA), and other organizations. The OSHA Permissible Exposure Limits (PEL) and National Ambient Air Quality Standards (NAAQS) data provide the maximum acceptable pollution level for various substances . We assume that the scientists working for these agencies determined the these limits based on proper toxicity evidence. Thus, if the acceptable exposure for one substance is set to 15 micrograms/m3, and for another it is 3 micrograms/m3, we will consider the relative toxicity of the second substance as 5 times greater than the first.

Note that even though the levels for the same substance in different tables are different (since they can be "permissible" levels for 8-hour exposure, or for year-round exposure), we can still compare the relative toxicity.

In particular, we found the following PELs for some of the common pollutants (all in mg/m3): mercury 0.01, benzene 3.2, lead 0.05, uranium 0.05, xylene 435, arsenic 0.01, carbon dioxide 9000, carbon monoxide 55; and the following numbers for ambient air standard (all in micrograms/m3): carbon monoxide 10000, lead 0.15, nitrogen dioxide 100, sulfur dioxide 78.

Finally, the relative "toxicity" of various greenhouse gases, that is, their "global warming potentials (GWP)" are taken from Wikipedia. The GWP of carbon dioxide is defined as 1, the other gases (in 20 year timescale) have the following GWP: methane 72, nitrous oxide 289, CFC-12 whooping 11000.