NASA Studies High Springtime Ozone Levels Over Canada and the
The high springtime ozone levels in the lower atmosphere at high
northern latitudes, such as over Canada and the Arctic, are caused
by the long-range transport of air pollution and not by natural
processes in the atmosphere.
A NASA Langley Research Center scientist and his
co-investigators from NASA Langley, the National Center for
Atmospheric Research (NCAR), and several universities will present
this result at the American Geophysical Union (AGU) spring meeting
in Boston, May 29 to June 2. The finding stems from a NASA
Langley-led investigation that was one of many studies in the
Tropospheric Ozone Production about the Spring Equinox (TOPSE)
field experiment funded by the National Science Foundation and led
by NCAR. Results will be presented for the first time from TOPSE at
the AGU Spring meeting.
Background levels of ozone exist in the lower atmosphere at all
times, but a peak occurs during the springtime at high northern
latitudes. The timing of the peak is unusual because other areas,
such as over most of the United States, experience their highest
seasonal ozone levels during the summer.
"Springtime ozone levels in the high northern latitudes have
been increasing with time, and we wanted to understand if this was
a natural process or not," said Edward Browell, head of the Lidar
Applications Group at NASA Langley and lead-author of this
investigation. Scientists have known for many years from
ground-based and balloon measurements that ozone amounts were
higher in the high latitudes of the Northern Hemisphere during the
spring than in other seasons.
Scientists determined that these higher springtime ozone amounts
could not be explained by an increase in the natural transport
process called stratosphere-troposphere exchange. This process
mixes ozone-rich air into the troposphere (the atmosphere from the
surface to 8-10 kilometers at high latitudes) from the stratosphere
(the atmospheric layer above the troposphere).
From field experiments, researchers found that long-range
transport moved air pollution into remote Arctic areas during the
winter and into the spring. In the springtime, processes convert
some of the air pollution into ozone in the troposphere. Ozone is
produced by photochemical processes that begin when sunlight comes
into contact with chemically active molecules like those found in
the air pollution. Scientists concluded the transported pollution
was responsible for causing the production of the highest seasonal
ozone levels over Canada and the Arctic.
"Its important to study these remote regions to better
assess the relative impact of human activities versus natural
processes. If we separate those processes, we see the effects of
human activities all over these areas," Browell added.
From February to May 2000, researchers made seven flights to
high latitudes from Broomfield, Colorado with bases in Churchill,
Canada and Thule, Greenland. They took remote lidar measurements of
ozone and aerosols above and below the aircraft and integrated them
with meteorological analyses, chemical model results, and in situ
measurements to arrive at their conclusions.
Browell will present the results of this TOPSE investigation on
Tuesday, May 29, in the Convention Center, Room 311, Session A22B
at 2:30 p.m.
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