Geoscience Reference
In-Depth Information
Table 9.4.
Comparison of indoor workplace standards with outdoor federal and California State standards
for selected gases
Indoor
8-hr PEL and
TWA-TLV
a
(ppmv)
Outdoor
California
standard
(ppmv)
Indoor
15-min STEL
a
(ppmv)
Indoor
ceiling
a
(ppmv)
Outdoor
NAAQS
(ppmv)
Gas
Carbon monoxide
35
-
200
9.0 (8-hr)
9 (8-hr)
Nitrogen dioxide
-
1
-
0.053 (annual)
0.18 (1-hr)
Ozone
0.1
0.3
-
0.075 (8-hr)
0.07 (8-hr)
Sulfur dioxide
2
5
-
0.14 (24-hr)
0.04 (24-hr)
NAAQS, National Ambient Air Quality Standards; PEL, permissible exposure limit; STEL, short-term exposure limit; TWA-TLV, time-
weighted average threshold limit value.
a
National Institute for Occupational Safety and Health (2010).
healthier than is the average person. Table 9.4 also indi-
cates that the 15-minute STEL for nitrogen dioxide is
five times higher (less stringent) than is the 1-hour out-
door California standard. Stringent outdoor standards
for nitrogen dioxide are set because it is a precursor
to photochemical smog. Because UV sunlight does not
penetrate indoors, nitrogen dioxide does not produce
ozone indoors, and indoor regulations of nitrogen diox-
ide as a smog precursor are not necessary. Indoor stan-
dards for nitrogen dioxide are based solely on health
concerns.
workplace and in public buildings; residential air is not
regulated.
9.6. Problems
9.1. Why are ozone mixing ratios almost always lower
indoors than outdoors?
9.2. Why are workplace standards for pollutant con-
centrations generally less stringent than standards for
outdoor air?
9.3. What would be the volume mixing ratio (ppmv)
of
carbon
monoxide
and
the
mass
concentration
9.5. Summary
People spend most of their time indoors; thus, the qual-
ity of indoor air has a significant impact on human health
risk. Indoor air contains many of the same pollutants
as outdoor air, but pollution concentrations in indoor
and outdoor air usually differ. Although indoor mixing
ratios of ozone and sulfur dioxide are usually less than
are those outdoors, indoor mixing ratios of formalde-
hyde are usually greater than are those outdoors. Indoor
mixing ratios of carbon monoxide and nitrogen dioxide
are generally the same as or less than are those outdoors,
unless appliances or other indoor combustion sources
are turned on. Indoor concentrations of radon, asbestos,
and ETS, when present, are usually greater than are
those outdoors, giving rise to potentially serious health
problems for people exposed to these pollutants indoors.
Indoor air also contains VOCs, allergens, fungi, bacte-
ria, and viruses. A major source of human mortality
and illness worldwide is the indoor burning of solid
biofuels and coal for home heating and cooking. This
problem could be mitigated with current technologies.
In the United States, indoor air is regulated only in the
gm
−
3
)ofparticles if ten cigarettes were smoked in a
(
×
×
5
3-m room? How do these values compare with
the U.S. federal primary 1-hour standard for CO(g) and
24-hour average standard for PM (Table 8.2)? Based
on the results, which pollutant do you believe is more
of a cause for concern with respect to indoor air qual-
ity? Assume that the dry air partial pressure is 1,013
hPa and the temperature is 298 K, and use cigarette
emission rates from Table 9.2.
10
9.4. Why is radium less of a concern than radon?
9.5. Why is removing asbestos from buildings often
more dangerous than leaving it alone?
9.6. Why does the gas-phase chemical decay of organic
compounds generally take longer indoors than outdoors?
9.7. Identify three methods that could be used to reduce
indoor pollution or its exposure due to the indoor burn-
ing of solid biofuels and coal for home heating and
cooking.
9.8. Identify five indoor activities that could increase
your personal cloud concentration of air pollution.
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