Regional Haze Composition

Regional haze is caused by fine particles that scatter and absorb light before it reaches the observer. As the number and size of fine particles increase, the more light is absorbed and scattered, resulting in less clarity, color, and visual range (i.e. 'hazy' view).

In Class I areas (for more information go to ClassI.) in the MANE-VU region, including Maine, the primary component of regional haze on days with the poorest visibility is sulfate particles. Sulfate particles are formed from sulfur dioxide, mainly released by fossil fuel burning power plants and industrial boilers. Some of these sulfate pollutants are from local sources, while others originate elsewhere and are transported hundreds of miles into the region.

While the majority of sulfates come from human-made sources, some sulfate particles are released from natural sources such as tiny organisms at the ocean surface or volcanoes and wildfires. However, these are generally considered insignificant contributors to regional haze. Extreme events can cause regional haze. One such event was the wildfire event in July of 2002 that contributed to both elevated ozone as well as regional haze for much of the eastern seaboard.

In Maine at the Acadia monitoring site, sulfates account for one-half to two-thirds of the total fine particle mass -- but result in two-thirds to three-quarters of visibility impairment.

During the warmer months (April - September) the second largest component of regional haze at Acadia, contributing about one-fourth to one-third of the fine particles is organic carbon. Major sources of organic carbon include cars, trucks, non-road vehicles such as construction equipment and natural emission sources, such as wildfires.

Conversely, during the colder months (October through March) nitrates are the second largest component of regional haze. Major sources of nitrates include cars, trucks, and non-road vehicles such as construction equipment. Nitrates often appear brownish in color, which explains the 'brown cloud' sometimes seen hanging over urban areas in the winter months. 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. Brown clouds are a more localized pollution event and usually are not 'regional haze'.

2002 Fine Particle composition data from Acadia National Park is graphically presented below.

This data, from VIEWS , was categorized by degree of pollution on a given day. The worst 20% and best 20% are displayed along with the daily average for the year. (The IMPROVE network monitors every third day. So each year 121 to 122 samples are taken. Therefore, 20% = 40 days) The data was taken from a query and placed into an Excel spreadsheet. The charts above were created using the Excel chart wizard. Data for other sites around the country is available on the VIEWS web site.

To see images of best and worst days go to the visibility page.

Meteorology

Regional Haze Composition