Environmental Engineering Reference
In-Depth Information
TABLE 9.3
U.S. 2000 National Ambient Air Quality Standards (NAAQS)
Primary
Secondary
µ
g/m
3
µ
g/m
3
Pollutant
ppm
ppm
Carbon monoxide (CO)
8-h average
10 mg/m
3
9
40 mg/m
3
1-h average
35
Nitrogen dioxide (NO
2
)
Annual arithmetic mean
0.053
100
Same
Same
Ozone (O
3
)
a
3-y average of annual fourth highest daily
maximum 1-h concentration
0.12
236
Same
Same
Particulate matter, diameter
<
10
µ
m (PM-10)
b
Annual arithmetic mean
50
Same
Arithmetic mean of 24-h 99th percentile,
averaged over 3 y
150
Same
Sulfur dioxide (SO
2
)
Annual arithmetic mean
0.03
80
24-h average
0.14
365
3-h
0.5
1300
a
Proposed new standard: 3-y average of annual 4th highest daily max. 8-h concentration, 0.08 ppm
=
157
µ
g/m
3
.
b
Proposed additional new standard for particulate matter, diameter
<
2.5
µ
m (PM-2.5): 3-y annual arithmetic
mean, 15
µ
g/m
3
; arithmetic mean of 24-h 98th percentile averaged over 3 y, 65
µ
g/m
3
.
atmosphere is to be prevented as much as possible by applying at the sources Maximum Achievable
Control Technology (MACT).
The NAAQS for the five criteria pollutants are listed in Table 9.3. Primary standards relate to
human health effects, and secondary standards relate to “welfare” effects. The NAAQS definitely
have an anthropocentric aspect—that is, they pertain to human health and welfare—but it is un-
derstood that the welfare standards are for protecting the environment in general. The averaging
times can be as short as one hour (for CO) to one year (for PM, SO
2
, and NO
2
). The reason is that
the exposure of some pollutants at a high concentration for a short period may cause acute effects,
whereas the exposure of others at a relatively low level for longer periods may cause chronic effects
(see below). The number of allowed “exceedances” is also listed. For example, the 1-hour standard
for CO, 40 mg/m
3
(9 parts per million by volume, ppmV), must not be exceeded more than once per
year. The O
3
standard is 0.12 ppmV, 1-hour average, not to be exceeded more than once per year.
Recent health and ecological studies indicated that ozone may be harmful at a lower level when
exposed for a longer period, so a new standard has been proposed of 0.08 ppmV, 8-hour average.
Likewise, a new PM standard has been proposed. Currently, only particles with an aerodynamic
diameter of less than 10
m are regulated (PM-10). However, recent epidemiological studies indi-
cated that particles smaller than 2.5
µ
m are most detrimental to health, because they lodge deeply
in the lung's alveoli. Thus, in addition to PM-10 a PM-2.5 standard may be implemented.
The EPA is mandated to revise the NAAQS from time to time, as more results from health and
environmental effects studies become available. For example, EPA has been urged to promulgate
a short time standard for NO
2
instead of the annual standard.
µ
