Stack Opacity Estimator - EPA Method 9 Opacity to PM Emission Rate Conversion
Method 9 readings in. A screening PM rate out, with the correlation limits stated plainly.
Check a visible stack opacity reading by severity band and against the common 20% / 6-minute-average opacity prompt, with EPA Method 9 reading guidance (observer certification, sun position, background contrast, steam vs smoke). Severity bands are general industry framing. The tool does not convert opacity to PM mass, look up source-category limits, or determine compliance - actual limits, averaging times, and exceptions are set by your subpart, SIP rule, or permit.
Compare source-reviewed combustion PM values with opacity records
Fuel Combustion Emissions Calculator →Estimate concrete batch plant dust to compare against your Method 9 opacity observations
Concrete Batch Dust Calculator →Check stack flow velocity and temperature to verify the conditions behind your opacity reading
Stack Flow Calculator →Evaluate baghouse or scrubber efficiency to model the opacity reduction from adding controls
Control Device Efficiency →How It Works
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Enter Observed Opacity
Input the opacity percentage (0-100). Standard Method 9 uses a certified reader observing the stack plume against a contrasting sky background at a specific angle to the sun.
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Read the Severity Band
The visual scale and reference table classify the reading from clean (0-5%) through severe (60-100%) using general industry framing.
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Check the 20% Prompt Calculator
See whether the reading sits within or above the common 20% / 6-minute-average prompt. Verify the actual limit, averaging time, and exception provisions in your permit or rule.
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Review Method 9 Guidance
Use the built-in reading guidance - observer certification, observation protocol, sun position, background contrast, and steam-vs-smoke discrimination.
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Document Observations
Record observation conditions (wind, sky, distance, angle) as required by EPA Method 9 for valid opacity readings. These details are needed for any enforcement-quality observation.
Built For
- Plant operators performing daily opacity spot-checks between formal observations
- Compliance staff triaging visible-emission readings before calling for a certified observer
- Boiler operators troubleshooting combustion problems indicated by increased opacity
- Environmental staff training on Method 9 reading protocol and severity framing
- Facility teams screening whether a reading warrants permit-limit verification or stack testing
Assumptions
- Opacity readings follow EPA Method 9 procedures with a certified observer.
- Severity bands are general industry framing, not regulatory categories.
- The 20% / 6-minute prompt is a common screening value; actual limits are rule and permit specific.
- Background sky contrast and sun angle meet EPA Method 9 observation requirements.
Limitations
- Does not convert opacity to PM mass - opacity-to-PM relationships are source-specific and require paired testing.
- Water vapor (steam plumes) can cause visible opacity that does not represent PM mass.
- Does not look up source-category or permit-specific opacity limits, averaging times, or exceptions.
- Not suitable for determining compliance - use a certified Method 9 observation, COMS data, or EPA Method 5 testing.
- Method 9 readings are subjective and vary between certified readers by up to 7.5% opacity.
References
- EPA Method 9 - Visual Determination of the Opacity of Emissions from Stationary Sources.
- EPA Method 5 - Determination of Particulate Matter Emissions from Stationary Sources.
- Ringelmann Smoke Chart (Bureau of Mines Information Circular 8333).
- EPA New Source Performance Standards (NSPS) opacity limits by source category.