| Text of Test Method 9 - Visual Opacity |
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| Visible Emissions Field Manual |
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| Visible Emissions Evaluation Procedures Course |
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| Collaborative Study |
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| Optical Properties and Visual Effects of Smoke Stack Plumes |
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| Section 3.12 of the QA Handbook, Volume III |
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FREQUENTLY ASKED QUESTIONS (FAQS) for Method 9
When performing a Method 9 observation, what is the correct procedure for calculating an opacity
average if one or more 15–second readings are missed (plume rolling, plume obscured by fugitive emissions, distraction, etc.)?
If, for any reason, a 15-second reading is not made, a dash should be placed on the data sheet for that
15-second interval, and an explanation should be provided in the comments section of the data sheet. Running averages
can include a time-lapse break in the opacity readings when caused by an event that would make taking a valid
reading difficult or impossible (for example, plume obscured by fugitive emissions, plume rolling, or an improper
background). Running averages should not include a time-lapse break when a valid reading could have
been made, but was not (e.g., because the observer had eye strain or was distracted). In calculating running averages,
you must still use 24 consecutive readings which are then summed and the total divided by 24 to yield the opacity
average. For a more detailed description of the procedure, see Sections 6.1 and 4.3.2, I and J
of the QA Handbook here.
Still have questions on this method? Contact the EMC
expert Jason DeWees at
dewees.jason@epa.gov .
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