Estimate Air Pollution with Emissions Factors (AP 42)

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The U.S. EPA can help you calculate "typical" air pollution from different emissions sources in the U.S. including fired heaters, refineries, agricultural, chemical and metallurgical industries, etc. Just check out this cool report, AP 42 Compilation of Air Pollutant Emission Factors.

AP 42 can be handy if you want to know some “average” pollution emissions for any kind of estimate or study.

Is it safe to put the brick kiln there? (Photo by joiseyshowaa)

AP 42 uses a very simple equation:

E = A x EF x (1-ER/100)

where the terms are:

  • E = emissions;
  • A = activity rate;
  • EF = emission factor, and
  • ER =overall emission reduction efficiency, %

These factors are defined in each section -- they vary, depending on the section you are reading.

Example: Pollutant NOx

Suppose I need to estimate the emissions of a large boiler. I know it is designed to be a low-NOx boiler, but otherwise have no specific information on the make or model. I go to the AP42 link above, and after hunting around I settle on section 1.4 natural gas combustion.

I read through Section 1.4, and decide that Table 1.4-1, entry “boilers > 100 MMBTU/hr; controlled – low NOx burners” is the emission factor that best fits my need.

Table 1.4-1 says that the emissions factor is 140 lb / MMSCF. That implies that for AP42 equation E = A x EF x (1-ER/100), in this case:

  • A is MMSCF of natural gas burned
  • EF is 140
  • I don’t see any applicable reduction factors anywhere in Section 1.4, so I ignore the 1-ER/100 term
  • E is the NOx emission in lbs. E = 140 * A

All I have to do is figure out how much natural gas I'm likely to burn (factor A) and I can easily get the emissions (factor E).1

Also, I see that the “emission factor rating” value is “A”. This is a rating that the AP42 authors used to show how statistically confident the EF is. A value of “A” implies they had a lot of sample data and this value is high quality. Good news. I can get more details on this sort of thing in the background document to section 1.4.

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  1. Question: does anyone want me to show how you might get factor A? []
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