proof of linear extrapolation of embassy pm2.5-aqi relationship above 500

Well, I’ve officially been called “geeky” on Twitter. I wear the label with pride. Not wanting to let my fans down, I decided to prove my earlier conjecture that the US Embassy linearly extrapolates the AQI-PM2.5 relationship from the EPA’s 400-500 range for concentration values above 500. As I noted before, this is NOT supported by regulatory language in the US, since the PM2.5 concentration almost never goes above 500.

Here’s a plot of the US EPA’s regulatory AQI-PM2.5 relationship definition (blue, stops at 500) as well as a smattering of data from the Embassy monitor (red). Looks pretty clear that the Embassy is just using the EPA’s same AQI-PM2.5 relationship from 400-500 for all values above that.

2 Responses to “proof of linear extrapolation of embassy pm2.5-aqi relationship above 500”

  1. FK says:

    EPA (USA) provides this relation (PM2.5 and AQI) that you tried to plot as above. Latest revision dated 14 Dec 2012 can be found on

    This formulae can also be found on

  2. Vance says:


    Thanks. I linked to the Dec 2012 revision in my previous post. This post here is showing the relationship >500, which is not defined in the EPA’s regulatory documents. I assumed it would be linear, and these data here prove it.


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