When particles are near or larger than the wavelength of the incident light, photons of all colors are scattered out of the beam path. --Figure 2.7, An Introduction to Visibility, National Parks Service 1999, ISSN 0737-5352-40
A visible emission is any visible airborne particle resulting from a chemical or physical process. Visible emissions often contain respirable particles, and can be measured by their effects on the opacity (or lack of transparency) of the air. Opacity is expressed as the percentage of light that is scattered or blocked by emissions, such that an observer's view through the emission is obscured. Examples of pollutants that can have opaque emissions include combustion products and dust.
Certifying community observers in EPA Method 9 for visual assessment of emissions can be written into a facility’s permits, read more in advocacy strategies.
photo by Mary Kenosian
Smoke School Certification
Citizens can get certified for visible emissions monitoring using EPA Method 9. This training is sometimes referred to as “smoke school,” Opacity Certification, Opacity Training, Visible Emissions Training, or VEO Training. Persons seeking certification take an online training course, where they learn about the history of visible emissions regulation and underlying reasons for conducting the method as instructed (e.g. keeping the sun at their back and having a shallow angle of vision between themselves and the plume source). Then, in smoke school, a smoke generator is used to create example plumes in both white and black smoke, and students learn to make visual estimates of relative opacity to within 5%.
Certification is valid in all states regardless of where it was obtained with the exception of Texas. There are several schools that will teach this method and certify those who complete the program. Certification can take a half day to two days, depending on who is administering the certification program. Method 9 and alternative methods (see below) can be conducted without certification, however familiarity with material in method 9 lectures and demonstrations is highly recommended (estimating smoke opacity is not intuitive!!), and without certification, enforcement may not be prompted.
To maintain your certification, you must pass the field certification test every 6 months. A list of other smoke schools can be found here, however Aeromaet is one of the cheaper options, takes less time and offers trainings in many locations. To get certified, you must attend a public training or arrange for a site training. The total cost of training through Aeromet varies slightly by location, and is $225 in Wisconsin (this is for online training materials- $40, and Field Certification cost $185.) The lecture material needs to be completed every 3 years and recertification needs to be done every 6 months.
When you receive your EPA Method 9 certification, it also allows you to perform EPA Method 203a, 203b and 203c tests.
Method 9, Determining Opacity
According to the WI DEQ: If you see dust you can assume the visible emissions are above 10% opacity. Observers stand with their back to the sun (the sun can be in a 140-degree range behind the observer) and as close as possible to perpendicular to the emissions plume. The observers and take visual estimations of how obscured the view is through the plume in accordance with their training, rounding to the nearest 5%. The EPA states “opacity shall be determined as an average of 24 consecutive observations recorded at 15-second intervals,” adding up to a 6 minute observation period.
Method 203a, b & c
Please see the EPA technical documents here.
“Method 203A is virtually identical to EPA's Method 9… except for the data-reduction procedures, which provide for averaging times other than 6 minutes." Method 203A is appropriate for emissions that are episodic with emitting durations between 2 and 6 minutes.
“Method 203B is virtually identical to EPA's Method 9... except for the data-reduction procedures, which have been modified to apply to time-exception regulations.” "A time-exception regulation means any regulation that allows predefined periods of opacity above the otherwise applicable opacity limit (e.g., allowing exceedances of 20 percent opacity for 3 minutes in 1 hour.)”
“Method 203C is virtually identical to EPA's Method 9…. except for 5-second reading intervals" instead of 15-second intervals. Method 203C is appropriate for short emission durations.
Method 22- uncertified observation of the frequency of visible emissions
Another method for measuring emissions visually is EPA Method 22. This method does not require certification, and does not evaluate the opacity of emissions. Rather, Method 22 "determines the amount of time that visible emissions occur during the observation period (i.e., the accumulated emission time)" and the frequency of opaque emissions. To conduct Method 22, the observer should be knowledgable about opacity and the effects of background color, sun angle, plume direction, siting distance, and water vapor. This information is in Method 9 lecture courses, and Method 22 suggests attendance at least one smoke school before performing a Method 22 test. While Method 22 is effective in reporting, it is only considered qualitative and not as powerful as Method 9 which is considered quantitative. Certain industrial practices are subject to Method 22 evaluations, such as gas flares, but for other industries, a Method 22 evaluation demonstrating prolonged periods of opaque emissions would only constitute ancillary evidence that perhaps an site is in violation of its Method 9 based regulations.
The WI DEQ regulates opacity for Fugitive Dust under NR 425.04 and NR 415.076. Fugitive Dust regulations state materials handling operations “shall have fugitive emissions controlled to 20% opacity when wind speeds are less than 25 miles per hour except for 3 minutes in any hour when fugitive emissions may equal 50% opacity.” DEQ also regulates opacity under NR 415.076: PM emission limitations for crushed stone, sand and gravel plants. This regulation states “...operator shall control fugitive emissions from a road or other area used by haul trucks and from drilling so that visible emissions do not exceed 20% opacity at the source…” and that “emissions from activities not associated with processing equipment, including but not limited to roads, other areas used by haul trucks, storage piles and drilling, shall be controlled so that visible emissions do not exceed 5% opacity at the source.”
Here is an example form that can be used for submitting information to the WI DNR on opacity.