| Tiny particles or liquid droplets suspended in the air that can contain a variety of chemical components are termed Particulate Matter (PM). Some particles are directly emitted into the air and come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and wood burning. Other particles are formed in the atmosphere by chemical reactions.
Particles less than 2.5 microns in diameter are termed PM2.5, and particles smaller than 10 microns are termed PM10. PM10 particles are visible as smoke or dust and settle out relatively rapidly, while the tiniest particles can be suspended in the air for long periods of time and contribute to haze in the atmosphere. They are also the most harmful to human health because they can penetrate deep into the lungs. Virtually all particulate matter from mobile sources is PM2.5.
How are we doing?
The State Department of Environmental Protection monitors PM in Suffolk County, using four sites in Boston and one in Chelsea. The annual mean for PM10 did not change much between 1994 and 2002; however, in 2003, the annual mean dropped 19% over the previous year and remained the same for 2004. Monitoring of smaller particles, PM2.5, began in 1999 at these locations. The annual mean concentration was similar in 1999-2001, and then dropped 19% in 2002. Based on this monitoring data, the federal Environmental Protection Agency has found that Boston currently complies with the air quality standard for fine particulates. However, the 2004 reading was up 11% over 2002. Although Boston has not been classified as a “nonattainment” area for fine particles, it will be important to continue monitoring and determine whether the 2004 increase represents an unhealthy trend.
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Click image to enlarge chart "Ambiant particle matter concentration, Suffolk County: 1994-2004"
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