The
Bishop Paiute Tribe uses two instruments to measure air quality.
Both measure the concentrations of small particles that may lodge
in the human lung and cause or exacerbate health problems. PM-10
refers to particles that are less than 10 microns in diameter (8
will fit in the diameter of a human hair). PM-2.5 refers to particles
that are less than 2.5 microns in diameter.
The instruments
used are Tapered Element Oscillating Microbalances, equipped with
the Filter Dynamics Measurement System (TEOM / FDMS). These are
sophisticated and extremely accurate monitoring devices. They measure
the concentration of particulates in micrograms per cubic meter
of air. A microgram is one-millionth of a gram. There are over 28
million micrograms in an ounce.
To ensure accuracy
of measurements, both the flow of the air through the instrument
and its temperature are precisely controlled.
The diagram
on the next page shows the inner workings of the TEOM / FDMS.
PRINCIPLES
OF OPERATION
The instrument operates on a simple principle. Particles are selected
for size and drawn into the instrument in a temperature-controlled
column. They are deposited on a filter that sits at the top of a quartz
element (the weighing device). This element oscillates at a known
frequency. As material accumulates on the filter, the frequency of
oscillation is changed in a way that is directly proportionate to
the mass of particulate. This frequency is measured every 2 seconds
along with the flow of air through the instrument and is used to calculate
the one-hour averages that are on the “Current air quality data
for the Bishop Paiute Reservation” link. |