April 2013: Ambient Monitoring in Indiana
Levels of criteria pollutants are measured at numerous locations around the state. This issue will discuss more specifics about monitoring.
PM-10 (Particles with a diameter less than 10 microns)
At the end of 2012, IDEM had 16 different sites in Indiana measuring PM-10. These were located in seven counties. Readings are taken every sixth day. This schedule has been selected by the U.S. Environmental Protection Agency so that each day of the week will be sampled equally. The sampler is similar to a vacuum cleaner. A motor pulls air through a filter. The filter is weighed before and after sampling. The difference in weights is the amount of material collected. The amount of air that goes through the filter is also recorded. The weight of material collected is divided by the amount of air to arrive at a concentration (normally in micrograms per cubic meter -- see Techie Note at the end of the article). The sampler is equipped so that large particles (those above 10 microns in diameter) are captured before they get to the filter.
PM-2.5 (Particles with a diameter less than 2.5 microns)
At the end of 2012, IDEM had 32 different sites in Indiana measuring PM-2.5. These were located in 21 counties. The sampling of PM-2.5 is similar to PM-10 except that the monitors are equipped to remove particles with a diameter above 2.5 microns so that they will not be captured on the filter.
Sulfur dioxide levels are measured at 20 sites in Indiana. These are located in 14 different counties. Sulfur dioxide is measured continuously, but data are stored as hourly values. Some of the sulfur dioxide sites in Indiana are operated by utilities. These sites are overseen by IDEM staff to ensure that the data meet quality assurance objectives and that the sites are run properly.
Four nitrogen dioxide sites are operated in Indiana in four different counties. Nitrogen dioxide is measured continuously, but data is stored as hourly values.
Forty-three ozone sites are operated in the state of Indiana. These are operated in 30 different counties. Ozone is measured continuously, but data are stored as hourly values. Ozone is sampled during the ozone season. For most of Indiana this is from April 1 to September 30. For Clark and Floyd counties the ozone season is from April 1 to October 31. We also run an ozone site in eastern Illinois to determine the amount of ozone that is blowing into Indiana.
Six carbon monoxide sites are operated in Indiana in four different counties. Data is measured continuously, but stored as hourly values.
Eight lead sites are operated in Indiana in four different counties. Data is sampled similar to PM-10 and PM-2.5, normally on an every sixth day schedule. The samplers are similar to PM-10 and PM-2.5 except that the instruments are not equipped to limit the particle size that is captured by the filter.
In addition to criteria pollutants, IDEM also monitors air toxics (which will be a separate issue) and meteorological data. Typically this includes wind speed, wind direction and temperature, but may include some other parameters as well.
IDEM publishes Continuous Air Quality data on the Web in near real time. There is usually a delay of about two hours. Interested parties can view pollutant levels and meteorological data. IDEM provides this list of pollutants of interest with relevant maps of sites. Each site of interest provides data for the current day. You can enter dates for other periods to review data from past months or years.
Additionally, IDEM provides additional information on our monitoring network. Information includes the Indiana Ambient Air Monitoring Network Plan, which describes in detail the locations and measurements made for each site.
Finally, IDEM also provides detailed information on monitoring.
Techie Note: A microgram is one millionth of a gram. One pound is equal to 453.6 grams. So a microgram is not very much. A cubic meter is approximately 27 cubic feet, or a cube that is three feet on each side. This is roughly equivalent to the size of a couch. The point is that a microgram per cubic meter is not a very high concentration of material.