Particle pollution, or particulate matter, consists of particles that are in the air, including dust, dirt, soot and smoke, and little drops of liquid. Some particles, such as soot or smoke, are large or dark enough to be seen. Other particles are so small that you cannot see them.
Particle pollution can come from primary or secondary sources. A primary source, such as wood stoves or forest fires, lets off particle pollution directly. A secondary source lets off gases that react and form particles. Examples of secondary sources are coal fires and power plants. Particle pollution also comes from motor vehicles, factories and construction sites. These can be primary or secondary sources. Particle pollution can be a problem at different times of the year, depending on where you live.
Particle pollution includes:
- coarse particles that are between 2.5 and 10 micrometers
- fine particles that are between 0.1 micrometers and 2.5 micrometers (also known as PM2.5)
- ultrafine particles that are smaller than 0.1 micrometers.
Particles bigger than 10 micrometers can irritate your eyes, nose and throat but do not usually reach your lungs. Ten micrometers is about seven times thinner than one human hair.
Fine and ultrafine particles are the size of most concern because they are most likely to cause health problems. Their small size allows them to get into the deep part of your lungs and even into your blood.
A crude rate is the number of cases or events in an area during a specified time period per unit population of interest such as "per 10,000 people" or "per 100,000 people."
Most health outcomes—cancers or heart disease, for example—occur at different rates in different age groups. A neighborhood with a high proportion of older people would be expected to have a higher unadjusted or “crude” rate of heart disease based on its age makeup alone.
Age-adjustment minimizes the impact of age differences when comparing two rates. Within Vermont Tracking, age-adjusted rates have been statistically adjusted to reflect the Year 2000 U.S. Standard Population. A crude rate does not make this adjustment.