Geoscience Reference
In-Depth Information
Because of its direct and indirect impacts on health and the environment, and spec-
tral properties that make it relatively easy to track, CO has been monitored globally
for a number of years. All or parts of all continents contain major emission generators
at one time of year or another, and the transported CO adds to the load at certain times
on all continents.
The CO is created primarily by incomplete fuel combustion. Primary sources, es-
pecially in developed areas, include vehicles and various industrial processes. Natural
and human-set vegetation fi res also are a signifi cant source. The concentrations of CO
that are added to local settings via long-distance transport usually are not considered
an added health burden on their own, Schoeberl says, but he notes that CO is “a great
tracer for human activities and biomass burning.”
The CO also plays a role in ground-level ozone formation. Several studies have
found that transport of CO from one location is associated with increased ground-level
ozone thousands of miles away. Examples include transport from North America to
Europe, from Alaska and western Canada to Houston, Texas, and from Asia to western
North America. Atmospheric CO also affects a number of other chemical reactions in
the atmosphere.
Ground-level ozone is created primarily through reactions among NO
x
, VOCs, and
other chemicals in the presence of sunlight. Ozone can cause health problems such as
premature death and a range of respiratory and cardiovascular disorders.
Studies conducted over the past 15 years or so that are based on airplane data,
ground monitors, and other instruments have provided substantial evidence that long-
distance transport of ozone can affect other countries and continents. For instance,
a report by Arlene M. Fiore and colleagues in the August 15, 2002
Journal of
Geophysical Research
noted that transport from outside North America can boost
ground-level ozone by 15-35 ppb on summer afternoons in the US. These imports of
ozone can, in some places on some days, spike levels in some counties above the EPA
standard of 75 ppb.
The long-distance spread of ozone has played a role in the large increase in ozone
concentrations in many areas of the planet since about 1950, according to Roxanne
Vingarzan, a senior scientist with Environment Canada. In a July 2004
Atmospheric
Environment
article she reported that ozone concentrations around the globe have
roughly doubled since then. As scientists become more adept at using satellite imagery
to track long-distance ozone movement within the troposphere and down to ground
level, more detail should become available.
But the spectral properties of ozone make it diffi cult to take advantage of sat-
ellite instruments to track ground-level concentrations. “We have had satellites
measuring total column ozone for some time,” Keating says. The problem, he ex-
plains, is that 90% of the ozone is in the stratosphere, so “measuring ozone in the
troposphere requires looking through the stratosphere for the proverbial needle in
a haystack.”
