About carbon monoxide in Spokane:
Carbon monoxide (CO) is odorless and colorless
gas that is produced naturally by both biological and abiotic sources
(such as wildfires and volcanoes); natural air contains about 0.02
to 1 ppm of CO. CO is also a common byproduct of incomplete combustion
of materials such as tobacco, wood, coal and petroleum derivatives
(oil and gas). Automobile exhaust is rich in carbon monoxide, along
with its more oxidized cousin, carbon dioxide (CO2).
About 60% of anthropogenic CO comes from automobiles.
Carbon monoxide interferes with proper respiration
in animals, by its very efficient substitution for molecular oxygen
(O2) in red blood cells. Breathing
air laden with carbon monoxide can quickly lead to an oxygen deficit
in the bloodstream, and can impact health, especially among those
with pre-existing respiratory problems and heart conditions. Carbon
monoxide can build up in an automobile-rich urban environment, especially
during poor atmospheric conditions such as no wind (stagnant air is
typical of skyscraper-bounded streets) and a density inversion (often
in winter, when automobile combustion is also inefficient). The Environmental
Protection Agency has set CO standards of 9 ppm averaged over 8 hours
and 35 ppm averaged over 1 hour.
The Washington State Department of Ecology has
established real-time air quality monitoring stations in selected
localities, to measure various pollutants such as CO, fine particulate
matter, and ozone. These data are posted on the web (see below). The
data shown here were collected in downtown Spokane, a city of 250,000
in easternmost Washington. The data have already been "smoothed"
through calculation of a running 8-hour average, to better compare
with the EPA standard.
We show the smoothed data, rather than the original
values, to emphasize the cyclical nature of street-level carbon monoxide
concentrations. As one might expect, CO peaks around the evening rush
hour, and then declines steadily until the morning traffic surge.
Superimposed on this cyclical behavior is a linear trend of declining
carbon monoxide concentrations over the three days shown. What might
be the cause of this decline?
Students can model the CO concentrations by first
subtracting the linear decrease, to discover a damped oscillation.
The damped oscillation can then be modeled with a sine function. Monday's
late morning data will be underestimated by the model; why?
Source: Washington State Department of Ecology http://airr.ecy.wa.gov/Public/aqn.shtml
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