Visible Emissions

Various industries produce visible emissions (VE). They are introduced into the Photograph of Visible Emissions from 2 Smoke Stacks atmosphere by sources such as stacks, vents, process equipment, combustion and incineration.

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 visual range in urban, rural and wilderness areas.

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 limitations. 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.

In the 50's and 60's Los Angeles added two major refinements to the visible emissions observation method. One was training and certifying inspectors using a smoke generator equipped with an opacity meter. Certified inspectors no longer needed to carry and use Ringelmann cards. Also, the Ringelmann method was expanded to white and other colors of smoke by the introduction of the idea of "equivalent opacity". Equivalent opacity meant that white smoke was equivalent to a Ringelmann number in its ability to obscure the view of a background. In some states, equivalent opacity was still measured in Ringelmann numbers while in others the 0 to 100% scale was used. In the 60's, the Federal Government published AP-30 describing accuracy of smoke reader's observations when compared to a transmissometer. It also addressed the problem of viewing a plume with the sun in the wrong place relative to the source.

EPA stopped using Ringelmann numbers when EPA Method 9 procedures for New Source Performance Standards (NSPS) were published in 1974, unless required by a State Implementation Plan. Current NSPS procedures are based solely on opacity. 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%.

	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.
	Maine's Visible Emission Limits
	Maine's Visible Emissions Regulation (Microsoft Word Document 43 kb) sets opacity limitations for emissions from various categories of air contaminant sources.

What Constitutes a Visible Emissions Violation in Maine?
According to Method 9, a violation of a six minute opacity standard has occurred if the average of any group of 24 consecutive readings (six minutes) in a one-hour period exceeds the standard. Sources subject to federal New Source Performance Standards must calculate opacity as specified in Method 9, unless stricter standards are in effect. In Maine, the standards in the State's Visible Emission Regulation or a facility's air emission license will often take precedence.

VE Observer Training
Each April and October, the Department offers Visible Emission Training and Certification in Augusta and sometimes in other locations to state and industry personnel through its contractor, Morrison Environmental Engineering (MEE). "Method 9 Visible Emissions Observers" are required to renew their certification every six months. For more information about this training, contact MEE by phone: (207) 846-9897 or email: meeinc@maine.rr.com . Registration forms can be found on the Department's Internet site two months before each training.

Photograph of Smoke Generator and Observers at VE Observer Training in Augusta

Consequences of Non-compliance
Failure to comply with the visible emissions standard may result in enforcement action by DEP with possible penalties assessed.

For More Information
Guide to Visible Emissions Evaluations (Adobe Acrobat File 136 kb, 4 pages), written by Idaho's Department of Environmental Quality, describes visible emissions certification requirements and procedures, observation techniques, and how to calculate opacity. Please be aware that certain portions of this document will not apply to licensed sources in Maine.

To obtain a Visible Emissions Observation Form, to be used when conducting a visible emissions evaluation, contact DEP's Air Quality Compliance Section by phone: (207) 287-2437 or download the form from the Internet: http://www.state.me.us/dep/air/compliance/VEForm.pdf (Adobe Acrobat File 20 kb)

This information summarizes Maine's visible emissions requirements and is not intended to be all-inclusive. Detailed requirements are outlined in DEP's Visible Emissions Regulation (Microsoft Word Document 43 kb).

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Visible Emissions