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| A wide range of industries produce visible
emissions. They are introduced into the atmosphere by sources such
as stacks, vents, and conveyor lines. |
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| What Are Visible
Emissions? |
| Visible
emissions are comprised of a variety of particulate matter ranging
in sizes from 0.1 micrometer to 200 micrometers in diameter (compared
to the average human hair, which is 70 micrometers in diameter).
Particles
are categorized as:
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| • Smoke |
• Dust |
• Fumes |
| • Soot |
• Fly Ash |
• Liquid Droplets |
Particles
also are formed in the atmosphere by condensation or transformation
of emitted gases, such as sulfur dioxide, nitrogen oxides, and volatile
organic compounds, into tiny droplets. |
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| What Are the Impacts
of Visible Emissions? |
| Inhaled
particles can be hazardous to your health. Smoke and dust are the
most common types of visible emissions. They are comprised of inhalable
particulate matter made up of microscopic solid or liquid particles.
Major human health concerns include effects on breathing and respiratory
functions, aggravation of existing respiratory and cardiovascular
disease, alterations in the body's defense systems against foreign
materials, damage to lung tissue, carcinogenesis, and premature
death.
Particulate
matter also may injure crops, trees, and shrubs, and may damage
metal surfaces, fabrics, etc. Fine particles also impair visibility
by scattering light and reducing the visibility. |
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| How Are Visible Emissions
Measured? |
| The
Ringelmann Chart was developed in the late 1800s and became one
of the first tools used to measure visible emissions. Introduced
into the United States in 1897, it was soon accepted as the standard
measure of black smoke density and later adapted for gray, white,
and other colors of smoke plumes. This then became the basis for
many city, state, and federal regulations on smoke density. The
Ringelmann Chart is based on the premise that the darker the plume,
the more particles are present to block the light and reduce visibility.
Plume
opacity is measured in percent: the greater the opacity, the more
the background behind the plume is obscured and the less light can
come through the plume. If none of the background is obscured, then
the opacity is 0%. If the entire background is obscured, then the
opacity is 100%. |
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EPA
Reference Method 9 |
| EPA Reference Method 9
is found in 40 CFR Part 60, Appendix A. It was adopted as a visible
emissions inspection method in an effort to standardize the training
and certification of observers and to ensure that reliable and repeatable
opacity observations could be conducted anywhere in the United States.
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Idaho
Visible Emissions Limit |
| Idaho's
methods for determining opacity are found in DEQ's Procedures
Manual for Air Pollution Control (1986). These procedures are
nearly identical to those contained in EPA Reference Method 9. Both
describe the requirements for training and testing opacity observers,
steps to follow, and data to record while documenting an observation.
The major
difference between Idaho's method for making opacity determinations
and Method 9 is how opacity exceedances are calculated. Idaho's
Rules for Control of Air Pollution in Idaho (IDAPA 58.01.01.625)
limit visible emissions from any point of emission to 20% opacity
for more than three minutes in any 60-minute period.
(Different
standards apply to six exempted sources. See the rules for more
information about these sources. Additionally, more stringent visible
emissions standards may apply to sources subject to Federal New
Source Performance Standards found in 40
CFR Part 60.) |
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| How Are Visible Emissions
Violations Measured in Idaho? |
| Businesses
that generate visible emissions can follow these steps to measure
compliance with Idaho's visible emissions standard: |
| Step
1: |
Count the number of readings
in excess of the percent opacity limitation (in most cases, 20%).
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| Step
2: |
Divide this number by four (each reading
represents 15 seconds) to find the number of minutes in excess of
the percent opacity limitation |
| Step
3: |
If the opacity limit has not been exceeded
for more than three minutes, no violation has occurred. |
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| Because
Method 9 calculates opacity differently than the Idaho rule, sources
subject to federal New Source Performance Standards must calculate
opacity as described above and as specified in Method 9.
According
to Method 9, a violation has occurred if the average
of any group of 24 consecutive readings
(six minutes) in a one-hour period exceeds the standard. |
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| Consequences of
Non-Compliance |
| Failure to comply with
the visible emissions standard may result in enforcement action by
DEQ with possible penalties assessed. |
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| For More Information |
| Air
Quality in Idaho: Measuring Visible Emissions at Your Facility
(DEQ Publication,
January 2003: pdf 34 kb, 2 pages) |
| Guide
to Visible Emissions Evaluations
(DEQ Publication, January 2003: pdf 136
kb, 4 pages)
Describes
visible emissions certification requirements and procedures, observation
techniques, and how to calculate opacity. |
| Contact DEQ's Air
Quality Division at (208) 373-0502 to obtain a Visible Emissions Evaluation
Form to be used when conducting a visible emissions evaluation. |
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Note:
This information summarizes Idaho's visible emissions requirements
and is not intended to be all-inclusive. Detailed requirements
are outlined in DEQ's Rules
for the Control of Air Pollution in Idaho (IDAPA 58.01.01.625).
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