Haze occurs when fine particles in the atmosphere scatter light, limiting the distance that people can see, and obscuring the color and clarity of their view. Unlike ground-level ozone (smog), which is primarily a summertime problem, haze can occur at any time of the year.

Is it Hazy Today?

The live views of Boston below can show if haze is present and illustrate how haze can obscure our views. They are part of a network of real-time haze cameras called CAMNET that monitors scenic urban and rural areas and collects pollution and meteorological data to determine the causes of haze.

Compare the live images of Boston to the example images of clear and hazy days beneath them. Haze can be yellow, brown or red-colored when there is a high concentration of nitrogen oxide pollution in the air.

View from Blue Hill Observatory, Milton
View from Swampscott

Examples of Good & Bad Days

Clear Day: June 16, 1999

Example of a Clear day June 16 1999  

This is a typical clean, clear day in Boston. Note the crispness of the features on the horizon. These days will have low pollution levels and low humidity.
Fine Particles = 4.8 ug/m3 | Relative Humidity = 19%

Hazy Polluted Day: June 7, 1999

Example of a Hazy Polluted Day: June 7, 1999  


This is a typical hazy polluted day in Boston. Note the relatively uniform white haze that obscures the horizon. The haze tends to diminish slightly at higher elevations. These events tend to occur on hot and humid summer days and are affiliated with high ozone, fine particle and humidity levels.
Fine Particles = 16.7 ug/m3 | Relative Humidity = 45%

Below right is an example of a winter haze event, with the image on the left for comparison.


Examples of good & bad Haze days (Winter comparison to Summer)

Source: MANE-VU Contribution Assessment


Why Are We Worried About Haze?

  • Preserving our National Heritage. Every year, more than 280 million visitors travel through 156 national park and wilderness areas. Unfortunately, many of these people are unable to enjoy the spectacular vistas they come to see. In many eastern parks, visibility has been reduced from 90 miles to between 15 and 25 miles because of regional haze from man-made air pollution.
  • Health Risks. Most of the pollution that causes regional haze is not emitted directly into the air, but forms after gases emitted from pollution sources are transformed in the atmosphere into fine particles. These fine particles can be transported great distances by the wind and have been linked to serious health problems.

Learn more about health problems from particle pollution .

Where Does Haze Come From?

Five types of fine particles contribute to haze: sulfates, nitrates, organic carbon, elemental carbon (soot), and crustal material (e.g., soil dust, sea salt, etc.). The importance of each type of particle varies across the U.S. and from season to season. The chart below from the Visibility Information Exchange Web System (VIEWS) gives their relative contributions to the haze problem in Massachusetts.


Particles That Contribute to Haze in Massachusetts

Source: Based on Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring data for the 20% worst visibility days (% contribution to light attenuation) from Ware (Quabbin Summit) for 2007 from VIEWS. 


The major manmade sources of the pollutants that cause haze in New England are: power plants, boilers at industrial, commercial, and institutional facilities, cement kilns, lime kilns, oil furnaces and residential wood combustion (fireplaces, woodstoves, outdoor wood-fired boilers). Learn more from Northeast States for Coordinated Air Use Management (NESCAUM) and Mid-Atlantic/Northeast Visibility Union (MANE-VU).


What We Are Doing to Reduce Haze

The federal Clean Air Act (CAA) authorizes the U.S. Environmental Protection Agency (EPA) to address visibility in national parks and wilderness areas. In 1999, EPA issued the Regional Haze Rule requiring states and interested tribes to address haze caused by numerous sources over large geographic areas.

This created the Mid-Atlantic/Northeast Visibility Union (MANE-VU), one of five regional planning organizations established by EPA to address regional haze. Massachusetts is part of MANE-VU.


Mid-Atlantic/Northeast Visibility Union Map


The goal of the EPA Regional Haze Program is to achieve natural background visibility conditions (pristine) in all Class I areas by 2064. These include 156 National Parks and Wilderness Areas, 7 of which are in the MANE-VU region (see map at right). To reach the goal, the regional planning organization will study and measure the problem and then create controls to reduce haze.

MANE-VU represents Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, the Penobscot tribe, Rhode Island, St. Regis Mohawk tribe and Vermont, as well as federal environment, forest, park and wildlife agencies. MANE-VU also works with Northeast States for Coordinated Air Use Management (NESCAUM) and the Mid-Atlantic Regional Air Management Association (MARAMA).

What You Can Do

Of the steps you can take to reduce particle pollution that contributes to haze, most revolve around energy conservation and efficiency at home:

  • Be sure to insulate your home, use a programmable home heating and cooling thermostat, buy appliances, and unplug electronics and battery chargers whenever you're not using them.
  • If you buy a woodstove, look for an EPA-certified unit, which is better for air quality and your family's health, and only burn seasoned wood.  For additional information, see Heating Your Home with a Wood-Burning Appliance .
  • Keep your natural gas- or oil-fired furnace in good operating condition through regular tune-ups.

These practices will not only save you money in the long run but also reduce particle pollution from the combustion of fuel at home and by the power plants that provide your electricity.

Learn More

The sites listed below provide more information about haze and visibility.  Most links exit the MassDEP website.

CAMNET - Real-Time Air Pollution & Visibility Monitoring

Home Page
CAMNET web site

Causes of Poor Visibility
CAMNET web site

Colorado State University

Interagency Monitoring of Protected Visual Environments (IMPROVE)
IMPROVE web site

Visibility Information Exchange Web System (VIEWS)
VIEWS web site


Air quality data & mapping from around the world.
DataFed.net web site

MassDEP State Implementation Plan (SIP) Steering Committee

August 2008 Presentation: Regional Haze SIP
Web page

June 2008 Presentation: Regional Haze Control Strategies
Web page

Mid-Atlantic/Northeast Visibility Union (MANE-VU)

MANE-VU web site

Mid-Atlantic Regional Air Management Association (MARAMA)

MARAMA web site

Northeast States for Coordinated Air Use Management (NESCAUM)

Regional Haze page
NESCAUM web site

U.S. Environmental Protection Agency (EPA)

Visibility Page
EPA web site

Visibility in Mandatory Federal Class I Areas, 1994-1998: A Report to Congress
EPA web site