How to Fill Out the Visible Emission Observation Form (EPA Method 9)

To fill out the visible emission observation form under EPA Method 9, a certified observer completes the header fields identifying the plant, source, observer, date, and initial conditions; positions themselves with the sun in a 140-degree sector behind them; records 24 consecutive opacity readings at 15-second intervals to the nearest 5 percent in the form’s grid; notes any gaps, steam interference, or changed conditions; averages the 24 readings; and signs the form as a sworn attestation.¹ Errors in any of those steps can invalidate the entire set.

Before You Start: Certification and Gear

Only a certified observer can produce a legally valid form. Certification lasts six months, after which the observer must retake the full field test.¹ The form has a field for your certification date, and an expired certification is one of the fastest ways for a reviewer to throw out an otherwise clean set of readings.

Method 9 is often called a “no instrument” test. That’s misleading. You still need several tools to produce defensible entries:

A digital timer that beeps every 15 seconds to keep intervals consistent.
A jewel-mounted, liquid-filled compass readable to the nearest 2 degrees, for wind direction and sun position.²
A clinometer or Abney level for vertical viewing angle, accurate to 2 degrees.
A rangefinder to record distance to the emission point, accurate within 10 percent.
A handheld GPS to fix your observation position within 10 meters.
A USGS 7.5-minute topographic map to confirm true north, declination, and background features.²
A clipboard, ballpoint pens (so carbon copies stay legible), rubber bands to hold the form down in wind, and blank observation forms.

The clinometer and compass are the items people most commonly forget. Arriving without one can force you to reschedule.

Filling In the Header

Before taking any readings, complete the header block. Method 9 Section 2.2 requires the plant name, emission location, facility type, observer name and affiliation, and the date. You also sketch your position relative to the source directly on the form.³

At the moment you begin the first set of readings, record the start time, your estimated distance to the emission point, approximate wind direction and speed, sky conditions (cloud cover percentage and cloud color), and the background behind the plume. Fill in those same fields again when you finish, because a six-minute window can shift. Double-check the emission location identifier before you start — writing “Boiler 2” when you actually observed Boiler 3 can void the entire record in enforcement proceedings.

Positioning Relative to Sun and Background

Your position determines whether the readings you enter on the grid are defensible. Method 9 requires the sun to sit in a 140-degree sector behind you: the angle formed by a line from the sun to you and a line from you to the observation point in the plume must be at least 110 degrees.⁴ A handheld “sundog” sighting tool confirms this in the field without trigonometry. Sun in front of or too far to the side means glare, and glare makes the readings indefensible.

Background matters too. For white or light-colored smoke, green foliage gives the best contrast. For black smoke, a clear blue sky works best. Low contrast biases your readings low; extremely high contrast pushes them above the true value.⁵ Note your background choice on the form so reviewers can assess whether conditions supported a valid observation.

Recording the 24 Readings

The core of the form is a grid where you record one opacity value every 15 seconds. Don’t stare at the plume. Glance at it momentarily at each 15-second interval and assign an opacity value to the nearest 5 percent — 0, 5, 10, 15, and so on up to 100.¹ The grid is organized by minute and second, so each row usually represents one minute (entries at 0, 15, 30, and 45 seconds).

A complete set is 24 consecutive readings, which takes exactly six minutes. The form typically has room for multiple sets in a single visit. Mark the start and end time of each set so the readings can be tied to the facility’s operating log for that window.

If the plume becomes temporarily invisible — blocked by a structure, or lost against the background — note the interruption in the grid using the codes your regulatory authority specifies. Do not guess at a value to fill the gap. Fabricating a reading is the kind of thing that unravels an enforcement case.

Write clearly. If you make a mistake, draw a single line through the wrong entry, write the correct value beside it, and initial the correction. No correction fluid, no scribbling over. Ambiguous digits invite challenges at hearing.

Reading Around Steam Plumes

Steam is not an emission, and readings must exclude condensed water vapor. Water vapor plumes are very white and billowy, with cloud-like mottling, thinning to wisps at the point where they evaporate.⁶

Method 9 treats two cases differently, and each affects what you enter on the form:

Attached steam plume: water vapor is visible right at the stack outlet. Take readings beyond the point where the steam is no longer visible, and record on the form the approximate distance from the outlet to your reading point.
Detached steam plume: the emission leaves the stack clear and water vapor condenses farther downwind. Read opacity at the outlet itself, before the condensation point, selecting the densest visible portion at that location.⁶

Reading through steam inflates opacity and can generate a false violation.

Calculating and Signing the Average

After a full set, add the 24 opacity percentages and divide by 24. That six-minute average is the value regulators compare against the facility’s permit limit.¹ Calculate each set separately if you completed more than one — don’t lump every reading into a single average.

Check the arithmetic before signing. An addition error can either mask a real violation or manufacture an apparent one that wastes everyone’s time during review. Your signature on the form is a sworn attestation that the recorded conditions and readings are accurate.

After You Sign: Submission and Retention

The completed, signed form goes to the regulatory body with jurisdiction, usually a regional air quality management district or a state environmental agency. Some accept digital uploads through compliance portals; others still require hard copies by certified mail.

Facilities operating under Title V permits must retain all monitoring records, including Method 9 forms, for at least five years from the date of the observation.⁷ Title V also requires monitoring reports at least every six months, with all deviations from permit requirements clearly identified. Agency staff will check the math, confirm your certification was current on the observation date, and verify that the reported sun angle and weather conditions were compatible with a valid observation.

Method 9 vs. Method 22

The visible emission observation form under Method 9 is not interchangeable with the Method 22 form. Method 9 measures opacity — how much light the plume blocks, expressed as a percentage. Method 22 measures the frequency of visible emissions, typically from fugitive sources like equipment leaks or open material handling rather than a defined stack.⁴ If the permit sets a percent-opacity limit, use the Method 9 form. If it turns on whether visible emissions occur during a defined window, Method 22 applies. Filling out the wrong form invalidates the observation regardless of how carefully you took the readings.

1
Environmental Protection Agency. Method 9 – Visual Determination of the Opacity of Emissions From Stationary Sources
2
Eastern Technical Associates. Opacity Testing Equipment – Method 9 Visible Emissions Equipment
3
Eastern Technical Associates. EPA Method 9
4
U.S. Environmental Protection Agency. Visible Emissions Field Manual – EPA Methods 9 and 22
5
Compliance Assurance Associates. Plumes and Backgrounds
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Compliance Assurance Associates. Where to Read a Smoke Plume for Method 9
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eCFR. 40 CFR 70.6 – Permit Content