Regional Haze

Regional Haze, a widespread blanket of haze from numerous sources, obscures views in pristine areas like national parks and wilderness areas and blurs skylines. Regional Haze often appears white but can be colored differently depending on the angle of the sun and is generally the result of fine particle pollution.

The images below are from the Acadia hazecam. Both images are from the twin cameras located on Schoodic Point, in Acadia National Park, pointing west to view Mt. Desert (the most famous part of Acadia National Park).

Polluted Day
Acadia NP Polluted day

Clean Day
Acadia NP Clean Day


'Haze' consists of particles, smoke, dust and moisture suspended in the air that impairs visibility. 'Regional Haze' refers to haze that impairs visibility in all directions uniformly.

Regional Haze can occur at any time during the year and is often transported over long distances crossing state and national borders.

In the Eastern U.S., Regional Haze comes from fossil fuel combustion including power plants, industrial boilers, industrial processes, and transportation such as cars and trucks.

The majority of the pollution causing Regional Haze is not released directly into the atmosphere, but forms after gases released from pollution sources are transformed through chemical reactions into fine particles.

Regional planning agencies have been formed across the United States. One such agency is MANE-VU-- the Mid-Atlantic/NorthEast Visibility Union. MANE-VU includes the following states: Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Maryland, Delaware and also the District of Columbia. Two Native American tribes are also part of MANE-VU: the Penobscot Indian Nation and the St. Regis Mohawk Tribe. The Federal agencies involved include EPA, the U.S. Forest Service, U.S. Fish and Wildlife Service and the National Park Service.

MANE-VU states are using EPA's guidance to calculate natural visibility conditions in the East which are estimated at over 100 miles in some locations. Under current polluted conditions, average visibility ranges from 40 to 60 miles. Under the most polluted conditions, regional haze reduces visibility to as low as just a few miles.

Maine is actively working with MANE-VU to reduce Regional Haze effects within the region as a whole and within the state. Part of this effort includes joining with EPA, other States, local environmental agencies, Tribes and Federal Land Managers to work together in reducing Regional Haze at national parks and wilderness areas in the State.

Fine particle pollution, which causes haze, affects human health and can have serious effects on animals, plants, lakes, streams, soils, and visibility in millions of acres of parkland and wilderness areas.

Unlike Regional Haze, air pollution can also appear as a localized brown cloud in wintertime. The brown appearance is caused by a higher level of nitrates from industry and transportation and usually occurs over urban areas. Brown clouds tend to occur on calm winter mornings during rush hour traffic when cold air is trapped near the ground by warmer air above due to temperature inversions. Another more localized phenomena is plume blight which occurs when pollutants are emitted into a stable atmosphere and transported in some direction with little or no vertical mixing. Plume blight appears as a narrow band or layer. Both brown cloud and plume blight can reduce visibility, however they are not widespread.

Efforts to Understand and Reduce Regional Haze

In order to reduce regional haze it is necessary to reduce emissions of fine particles (sulfates, nitrates and organic compounds) and those gases that react to form them (e.g. sulfur dioxides, nitrogen dioxides, elemental carbon, organic carbon and dust). It is the fine particles that are so efficient at scattering light and reducing visibility.

In 1999, the U.S. EPA issued the Regional Haze Rule to address poor visibility in federally protected parks and wilderness areas known as Class I areas (see below for more information). This rule requires each state to submit a State Implementation Plan (SIP) for Regional Haze every 10-years, a 5-year Progress Report after each SIP and set a target date of 2064 for achieving natural visibility conditions. Maine's Regional Haze SIP for the first 10-year planning period ending in 2018 was submitted to EPA in December 2010. The 5-year Progress Report was submitted to EPA in February 2016. The next SIP for the 10-year planning period ending in 2028 will be submitted to EPA this year.

In the Regional Haze SIP, states are required to assess key contributors to regional haze formation, develop plans to reduce sources of haze-forming pollutants and submit these plans to EPA. As part of that process, NESCAUM and MANE-VU states are working on monitoring networks, data analysis and computer modeling of regional haze. Additionally, MARAMA is working with state agencies on the emissions inventory necessary for the modeling effort and OTC is coordinating the various processes within and among these regional organizations. Use the links provided within this paragraph for updates on work being done by each organization.

Other federal regulations specific to emissions from fossil fuel combustion at power plants and industrial boilers and set National Ambient Air Quality Standards (NAAQS) have and will in the future reduce fine particle pollution, the primary cause of regional haze. These regulations, which must be implemented throughout the country, will help improve visibility and reduce health impacts from fine particles in areas beyond the national parks and wilderness areas. Using data downloaded from FED for Maine's Class I Areas, the chart below shows regional haze conditions continuing to improve for the 20% most impaired days.

chart Maine Class I area data

The U.S. EPA and Federal Land Managers at the U.S. Fish and Wildlife Service, U.S. Forest Service and the National Park Service work together to collect air quality data and strive to reduce haze and improve visibility in Class I areas. To further advance the scientific understanding of regional haze and fine particle pollution in the region, states, tribes and other organizations maintain regular permanent monitors measuring various pollution parameters, including fine particles at numerous locations in each state. The DEP runs a number of monitors around the State of Maine which monitor fine and coarse particle levels in the atmosphere.

Class I Areas

Class I areas are national parks exceeding 6,000 acres and wilderness areas and national memorial parks exceeding 5,000 acres and all international parks that were in existence on August 7, 1977. There are 156 Class I areas.

Acadia National Park and Moosehorn National Wildlife Refuge contain Class I areas located within Maine. Class I areas in close proximity to Maine are the Roosevelt Campobello International Park in Canada and the Presidential Dry River Range and the Great Gulf Wilderness Area in New Hampshire.

Acadia National Park
Acadia NP

Moosehorn National Wildlife Refuge
Moosehorn WR

Roosevelt Campobello International Park
Roosevelt Campobello IP

Presidential Range Dry River and Great Gulf Wilderness Areas
NH Class I areas


Use the links below to access more specific regional haze information.