Particulate matter has been monitored in New Hampshire since 1967. Total suspended particulates (all particle sizes) were monitored until 1987, when the National Ambient Air Quality Standard (NAAQS) for particle pollution was changed to a smaller particle size of 10 microns or less in diameter, known as PM10. The standard was changed again in 1997 and 2006 because it was found that the smaller particulates (PM2.5, known as fine particulate matter) caused the most adverse health effects. A more extensive monitoring network for PM2.5 was established statewide beginning in 1998.
Fine particle air pollution (PM2.5) can penetrate deep into the lungs when inhaled, possibly affecting the health of people with heart or lung diseases and respiratory conditions, as well as older adults and children. Fine particles also play a major role in the formation of regional haze. Regional haze degrades visibility and can diminish the enjoyment of natural and scenic areas. Therefore, states have been required to assess key contributors to regional haze formation, develop plans to reduce sources of haze-forming pollutants, and submit these plans to the U.S. Environmental Protection Agency by 2008.
Overall, particulate matter concentration trends in New Hampshire show a clear reduction in pollutant levels at all monitoring sites. The PM10 standard has not been exceeded since 1989, and most portions of the state have not exceeded the standard since 1982. Monitored values for PM2.5 have also recently remained under the standard, although values remain close to the level of the standard for both annual and 24-hour periods.
Particle air pollution contributes to several other air quality issues including acid rain and nitrogen deposition. Most particle pollution comes from industrial processing, construction, fuel combustion at power plants and industrial boilers, and from cars and trucks. The smallest particles (PM2.5) not only present a health risk, but because of their light mass are highly transportable and can cross state and international borders (see link to Air Pollution Transport Report under "Publications").