Carbon Monoxide (CO)

<p>
<strong>Characteristics:</strong> Carbon monoxide is a
colorless, odorless and tasteless toxic gas found naturally in
trace quantities in the atmosphere.
<p>
<strong>Sources: </strong> Natural CO sources include volcanic
eruptions, oxidation of methane, chlorophyll decomposition,
thunderstorms, forest fires and microbial action in the oceans.
Anthropogenic (human) sources all involve burning fossil fuels.
For example, motorized transportation, solid waste disposal,
wood
and agricultural burning, steel production and residential
heating are all sources of carbon monoxide. In Minnesota, the
major sources of CO in urban areas are motor vehicle emissions
and wood-burning.
<p>

</td></tr></table>

<table border=0 width=600 cellpadding=5><tr><td>

<strong>Concentration: </strong> The background concentration of
carbon monoxide varies with time and space. Average global
levels
are estimated to be 0.19 parts per million (ppm). Background
concentration of CO is highest in the fall when CO is released
during the decomposition of chlorophyll in leaves.
<p>
Daily variation of CO in urban areas is associated with the
workday transportation cycle. In major urban areas, average
hourly CO concentrations may range from a few ppm to more than
30
ppm.
<p>
Carbon monoxide is removed from the atmosphere by the action of
soil microorganisms or by reaction with hydroxyl radicals in the
atmosphere, converting CO to CO2.
<p>
<strong>Health effects: </strong>When carbon monoxide enters
the
bloodstream, it combines with hemoglobin in red blood cells 200
times faster than oxygen, reducing oxygen delivery to organs and
tissues.
<p>
At relatively low concentrations, carbon monoxide affects the
central nervous system. CO can reduce a healthy person's
ability
to perform manual tasks, and can especially affect pregnant
women, fetuses, anemic individuals and persons with
cardiovascular diseases. In healthy people, short-term exposure
to concentrations greater than 30 ppm will cause drowsiness. At
levels greater than 35 ppm, CO induces irritability, headaches,
rapid breathing, blurred vision, lack of coordination, nausea
and
dizziness. In individuals with heart disease, CO causes
shortness of breath and chest pain at levels as low as 10 ppm.
<p>

<strong>Ecological effects: </strong> At concentrations commonly
found in the ambient air, CO does not appear to have adverse
effects on plants, wildlife or materials. However, CO is
oxidized to form carbon dioxide (CO2) a contributor to global
warming.
<p>

<strong><font size=+1>Trends in Carbon Monoxide (CO)
</font></strong>
<p>
<strong>Carbon Monoxide Emissions </strong>
<p>
Carbon monoxide is produced by the incomplete burning of carbon
in fuel. Figure 1 is a pie chart showing major sources of CO
emissions in Minnesota in 1994. This figure shows that
transportation sources-- mainly highway vehicles--are the major
source of CO emissions in Minnesota. Statewide CO emissions in
1994 are estimated to be 1.7 million tons.
<ul>
<li>As shown, on-road (highway) vehicles account for an
estimated
69.4 percent (1,170,629 tons) of all carbon monoxide emissions,
the largest portion of CO emissions in the state. Within that
category, light-duty gasoline vehicles (cars, motorcycles and
diesel) are the primary sources.
<p>
<li>The second major contributor to CO emissions is non-road
(off-highway) sources, which contribute 17.6 percent (295,540
tons) of emissions. These emissions are primarily from gasoline
used in construction, industry, farm, lawn/garden equipment,
snowmobiles, boats and aircraft.
<p>

<li>Fuel combustion accounts for 5.5 percent (93,212 tons) of CO
emissions. Within this category, residential wood combustion
accounts for 86 percent (80,533 tons) of total fuel combustion,
or 4.8 percent of CO emissions in Minnesota. Electric utility
and industrial fuel combustion, primarily coal, also contribute
to CO emissions.
<p>
<li>The petroleum industry (refineries) contributes about 3.5
percent (58,771 tons) of CO emissions. Waste disposal (mainly
incineration) accounts for 2.5 percent (42,027 tons).
</ul>
<p>
Remaining sources constitute less than two percent of statewide
CO emissions and and are combined and shown as "other." This
category includes chemicals and allied product manufacturing,
metals processing, other industrial processing such as wood,
pulp/paper and publishing products.
<p>
<center>
<img src="../../artwork/coEmissions.gif" alt="CO Emissions
statewide" width=313 height=225 border=0>
</center>
<p>
<font size=-1><i>Data derived from EPA's Office of Air Quality,
Planning and Standards, Research Triangle Park, NC. </i></font>

<p><br>
<strong>Carbon Monoxide Emission Trends </strong>

<p>
From 1985 to 1994, Minnesota's total CO emissions decreased by
21% or 0.4 million tons. Figure 2 shows that 2.1 million tons
of
CO were emitted in 1985, compared to 1.7 million tons in 1994.
A
comparison of emissions from each major source shows the
reduction is primarily due to reduction in emissions from
highway
vehicles. However, between 1993 and 1994, total CO emissions
increased slightly, by 0.05 percent. This increase is mainly
due
to non-highway sources.
<p>
Although there was a decrease in total CO emissions over the 10
years, improvement in air quality may be offset in the future
because of the increasing number of vehicle miles traveled.
According to the Minnesota Department of Transportation (MnDOT),
the number of vehicle miles traveled (VMT) in the Twin Cities
metropolitan area have almost doubled since 1980 (Figure 3).
Minnesotans drive more than 42 billion miles each year
statewide.
<p>

<strong>Figure 2- CO trends in emission estimates, 1985-
1994</strong>
<p>
<img src="../../artwork/air/co-fig2.gif" alt="co-fig2.gif -
11.40
K" width=695 height=316 border=0>

<font size=-1><i>Data derived from EPA's Office of Air Quality,
Planning and Standards, Research Triangle Park, NC.</i></font>
<p>
<center>
<img src="/artwork/vmt.gif" alt="Vehicle Miles Traveled -- TC
area" width=450 height=216 border=0>

</center>

<p>
<strong>Carbon Monoxide Ambient Air Concentrations</strong>
<p>
<strong>Long-Term Carbon Monoxide Concentration Trends:</strong>
Both state and federal CO standards average the concentration
of
CO across specified time periods: one hour and eight hours.
The
one-hour national CO standard is 35 ppm; the one-hour state
standard is 30 ppm. The eight-hour federal and state standards
are the same: 9 ppm. These standards are upper limits for both
one-hour and eight-hour averages and may not be exceeded more
than once a year. Therefore, we look at the second-highest
eight-hour and second-highest one-hour average CO concentrations
for each site. If the second-highest values are greater than
the
standards, the site is out of compliance (has a violation) for
that year.
<p>
The 1984-1995 trends for CO concentrations at eight sites are
shown in Figure 4 for the annual second-highest one-hour average
and in Figure 5 for the annual second-highest eight-hour
average.
Annual values at each site are connected with a dashed line.
The average of the annual values (by year, across sites) is
plotted as a heavy solid line. Horizontal lines are added at
the
one-hour and eight-hour standards. Any dashed line crossing
over
the horizontal line is an exceedance, and the site(s) was not in
compliance that year.
<p>
As illustrated in Figure 4, the second-highest one-hour values
at
each site were lower than state and national standards.
Therefore, for the entire time period, all eight sites were in
compliance. From 1984 to 1995, the average second-highest
one-hour CO level decreased by 38 percent, from 15.2 parts per
million (ppm) to 9.4 ppm. However, between 1994 and 1995, the
annual second-highest one-hour average increased by 2.4 percent,
from 9.15 ppm to 9.4 ppm.
<p>
Figure 5 shows that, from 1984 through 1991, the second-highest
eight-hour annual values for CO at several sites were higher
than
the standards and, therefore, out of compliance. The sites
include Lexington-University/St. Paul (1987-89 and 1991),
Midway/St. Paul (1984-87 and 1989), downtown/St. Paul (1987-89),
downtown/Duluth (1986 and 1989) and downtown/St. Cloud (1985).
<p>
From 1992 through 1995, there were no violations of the
eight-hour standard at any sites. In spite of the 1984-1991
violations, the second-highest eight-hour annual values for CO
show a decline of 43 percent from 1984 to 1995, from 8.67 ppm in
1984 to 4.90 ppm.

<p>
In conclusion, long-term trends in both ambient air
concentrations and total CO emissions indicate steady
improvement. These improvements agree with the estimated 26%
reduction in highway vehicle emissions. Although there is
general conformity between overall trends in air quality and
emissions, it should be noted that emission changes reflect
estimated statewide totals, while ambient CO monitors are
frequently located to monitor local problems in urban areas.
<p>

<strong>Figure 4- CO trends for second-highest one-hour average
ambient air concentrations in
Minnesota: 1984-1995</strong>
<p>
<img src="../../artwork/air/co-fig4.gif" alt="co-fig4.gif - 9.03
K" width=741 height=332 border=0>

<strong>Figure 5- CO trends for second-highest eight-hour
average ambient air concentrations
in Minnesota:
1984-1995</strong>
<p>
<img src="../../artwork/air/co-fig5.gif" alt="co-fig5.gif - 7.65
K" width=709 height=301 border=0>

<p>
<strong>Summary:</strong> Long-term trends in ambient air
concentrations and emissions of CO reflect steady improvement.
These improvements closely correlate with reduction in highway
vehicle emissions.

<p>
From 1985 through 1994, CO emissions decreased from 2.1 million
to 1.7 million tons, a 21 percent decline. From 1984 to 1995,
the average annual second-highest one-hour and eight-hour
concentrations decreased by about 40 percent. It should be
noted
that between 1994 and 1995, the annual second highest one-hour
average increased by 2.4 percent. Although CO emissions data
for
1995 is not available at this time, the increase from 1994 to
1995 may be attributed to the increase in VMT, along with
consequent congestion. Overall, from 1971-1994 (at the time of
this analysis, 1995 data were not available), for most
monitoring
sites, the annual pattern shows a steady decline. The rate of
improvement, however, varied among different monitoring
locations.
<p>
From 1984 to 1991, the second-highest eight-hour average CO
levels at many sites exceeded federal and state standards.
According to EPA, when an area does not meet the NAAQS for one
of
the criteria pollutants, it may be designated
as "nonattainment."
The CAAA of 1990 further classified nonattainment areas based
on
the magnitude of an area's problem. Nonattainment
classification
may be used to specify which air pollution reduction measures
must be adopted and when the area must reach attainment. To
reach attainment status, a nonattainment area must meet the
NAAQS
and fulfill all CAAA requirements.
<p>
There were four nonattainment areas for CO in 1980, including
the
Twin Cities seven-county area and the cities of Duluth,
Rochester
and St. Cloud. In 1990, EPA changed Rochester's status to
"attainment." Later, the cities of Duluth and St. Cloud were
likewise redesignated as attainment areas. Only the Twin Cities
seven-county metropolitan area remains in nonattainment status.
The MPCA continues to work with EPA on redesignating the Twin
Cities area, too, which requires monitoring data showing no
violations of health-based CO standards for at least two years.
It also requires demonstration that the area will continue to
meet these standards for at least 12 years.
<p>
Although CO emissions decreased statewide between 1985 and 1994,
VMT per year in the Twin Cities metropolitan area have almost
doubled since 1980. VMT have also increased statewide and show
no sign of leveling off. Along with consequent congestion, this
increase in VMT may overwhelm the air quality improvement made
as
a result of lower emissions from individual vehicles.