Ozone and particles are formed in the atmosphere when pollutants mix and react in the presence of sunlight. These precursor compounds are emitted by a variety of sources, both natural (e.g. forests) and man-made (e.g. automobiles and power plants). Particles are also emitted directly by a number of sources (e.g. power plants and diesel trucks and buses).
In recent years, it has become increasingly evident that the most persistent air pollutants (e.g., ground-level ozone and fine particles) are inherently a regional problem requiring a regional approach. Finding effective solutions is particularly difficult in the case of ozone and fine particles since both of these pollutants are formed by a complex series of chemical reactions that occur in the atmosphere and involve pollutants emitted from a variety of sources, often far away and hence involving transport from long distances.
Nowhere is the regional nature of this problem more evident than in New England. There are currently several counties in southern New England where ozone and/or particulate matter (PM) levels exceed the standard established by EPA to protect public health and welfare. The number of counties in the region that are expected to violate EPA's proposed new standards is considerably greater (see figure). The bad air quality responsible for these violations can adversely impact the health of the region's citizens and the environment with serious consequences for the local economy.
The transport of polluted air within the Gulf of Maine plays an important role in shaping the air quality in coastal New England. The source of the polluted air is less clear. Re-circulation of pollution from urban areas within New England and long-range transport (e.g., from the Washington and New York corridor) both have to be considered. The conditions in the Gulf are also expected to play a role as the marine boundary layer is expected to act as a huge chemical reactor converting primary pollutants like nitrogen oxides and organics into more-toxic secondary pollutants like ozone and fine particles.
Some of the highest ozone concentrations in New England have been recorded at monitoring sites on or near the coast. These episodes can result from the re-circulation of polluted air from within the region or long-range transport from outside the region. A more complete understanding of the relative importance of local versus distant sources on air quality in New England is an important first step in the development of an effective plan to improve air quality for the citizens of the region.