There are presently 45 areas that violate
the current PM-10 standard. The form
of the PM-2.5 standard requires that the 3-year average (rounded
to the nearest 0.1 ug/m3) of the annual means from single monitors
or the average of multiple monitors must be at or below the level
of the annual standard and the 3-year average (rounded to the
nearest 1 ug/m3) of the ninety-eighth percentile values at each
monitor cannot exceed the level of the daily standard. In determining
attainment of the annual average standard, an area may choose
to use either the spatially averaged concentrations across all
population-oriented monitors or it may use the highest 3-year
average based on individual monitors. The annual standard is
15 ug/m3. The 24-hour PM-2.5 standard announced in 1997 was 65
ug/m3.
On
September 21, 2006, EPA announced that it revised the level of
the 24-hour PM-2.5 standard to 35 micrograms per cubic meter
(µg/m3) and retained the level of the annual PM-2.5 standard
at 15 µg/m3. On October 8, 2009, the EPA announced the
designations for nonattainment for the PM-2.5 2006 standard.
The current number of areas that violate the PM-2.5 2006 standard
is 32
and the number of counties that violate is currently 121. A map
of the EPA's PM2.5 designations for nonattainment can be reviewed
by clicking
here.
