On April 14, 2020,
he Environmental
Protection Agency
( EPA )
announced there
would be no changes
to the National Ambient
Air Quality Standards
( NAAQS )
for particulate matter
( PM ).
PM includes fine particles
( PM2.5 )
and coarse particles
( PM10 ),
whose limits were
established in 2012.
“The U.S. has made
incredible strides in
reducing particulate
matter concentrations
across the nation,”
said EPA Administrator
Andrew Wheeler.
“As a result of Clean Air Act
programs and efforts by
state, local and tribal
governments, as well as
technological improvements,
average PM2.5 concentrations
in the U.S. fell by 39 percent
between 2000 and 2018
while average PM10
concentrations fell by
31 percent during
the same period,”
the EPA's press
release explained.
The Clean Air Act
requires the EPA
to set standards.
The primary NAAQS
are tough standards,
set at a level
“requisite
to protect
public health”
with an
“adequate
margin
of safety.”
The EPA sets annual
( long-term exposure )
and 24-hour
( short-term exposure )
primary NAAQS
for particulate matter.
The standards
are calibrated
in micrograms
per cubic meter
( µg/c3 ).
For PM2.5,
the current
annual
and 24-hour
standards are
12 µg/c3 and
35 µg/c3,
respectively.
The EPA looked at controlled
human exposure studies,
animal toxicology studies,
and retrospective studies
of health improvements
in areas with declining
PM2.5 levels.
The EPA did NOT find
a causal link between
mortality risk and PM2.5
exposures below the
2012 NAAQS standard,
so a more stringent
standard was not justified.
The EPA’s Clean Air
Scientific Advisory
Committee ( CASAC )
advised the agency
to retain the 2012 standards,
except for the primary annual
PM2.5 standard, where there
was no consensus.
The final judgment is by
the EPA administrator,
and he is NOT obligated
to follow CASAC’s advice.