White and black plumes can both obscure a background. Method 9 evaluates that obscuration as percent opacity; it does not assign a reading from smoke color alone.
Compare the reading conditions
White smoke
Black smokeFor both colors, judge how much of the background is obscured.
White smokeA white plume may be difficult to distinguish from a pale background. Assess its effect on background visibility, account for lighting, and determine whether condensed water affects the reading point.
Black smokeA dark plume against a light background can be easy to see. To assign a reading, estimate how much it obscures the background at the proper point in the plume.
These are observation considerations, not fixed opacity values for either color.
References: EPA Method 9, sections 2 and 3 and EPA Visible Emissions Field Manual. Consult the applicable rule or permit for your observation requirements.
Identify the background, the point you would read, and the factors that might change your estimate. Play the clip, then use the practice page to review how to record your observations.
Watch the sampleWhite appearance alone does not identify a plume’s composition. Condensed water must be handled using the method’s steam-plume procedure.
A dark plume can still allow background visibility. Do not infer opacity from a color label.
Method 9 qualification checks black and white plumes separately. Prepare for both and use verified reference values for accuracy feedback.
Yes. The method’s qualification process includes white and black plumes. Correct viewing conditions and the reading point still matter.
A photo alone does not establish a measured reference value. A public image without verified measurement data should not be presented as a scored exercise.
Review the complete observation sequence. Open the guide →
See how Method 9 differs from Method 22. Open the guide →
Try the unscored sample. Open the guide →