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TRACE: Seasonal Variability of Tropospheric Ozone
Fires Observed During TRACE-A |
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Intense smoke near
11° S, 30° E
(Northern Zambia)
October 6, 1992 |
The TRACE-A measurements clearly demonstrate that the
tropospheric ozone that accumulates over the tropical Atlantic ocean
between Africa and South America is a result of the wide spread
biomass burning that occurs on both of these continents during the
southern hemispherical spring and summer time. Shown here are some of
the fires that were observed from the DC-8 aircraft during TRACE-A.
Burning in both Africa and South America is, to a large extent,
associated with agricultural practicies that have been employed in
these countries for generations. Shown below are
AVHRR imagery over Brazil and Africa
during the TRACE-A study period. |
Typical Brazilia fire
near 9° S, 49° W
September 27, 1992
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Fire scar area near
11° S, 30° E
October 6, 1992
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AVHRR imagery over Brazil (top left image) cover the time
period during which the INPE aircraft were conducting meaurements. The
bottom left image covers the time period that both the DC-8 and INPE
aircraft were conducting coordinated flights in Brasil. The image in
the right panel depicts fires over southern Africa for
September-October, 1992. Both sets of images illustrate the extensive
amount of burning that occurs during the spring and summer time in the
Southern hemisphere. Measurements in the
ozone pool provides definitive "finger prints" of biomass
burning. |
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The TRACE-A mission provided the first opportunity for
direct sampling within the ozone pool. The results illustrated in the
right panel, along with other trace gas measurements aboard the DC-8
provided evidence clearly demonstrating that the satellite derived
tropospheric ozone residuals are valid and that the origins of this
ozone pollution is indeed associated with biomass burning. The top
panel on the right illustrates the extent of the ozone pool observed
from satellite measurements on the day of a DC-8 flight. The flight
path of the DC-8 is indicated by the dotted path along the coast of
Africa. The lower three panels show respectively the aerosol
distribution below the aircraft flight altitude from point A to B (
from the Differential Absorption Lidar (DIAL)), in situ measurements
of ozone and carbon monoxide as the DC-8 descended in altitude at
points A and B, and the distribution of ozone below the aircraft
flight altitude (also from the DIAL instrument). The DIAL and in situ
measurements clear show the elevated concentrations of aerosols,
ozone, and carbon monoxide in side the ozone pool.
The prevailing meteorology over
the Atlantic ocean serves to confine the ozone resulting from the
fires. |
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Emissions from burning in southern Africa and South America
are lifted to the upper regions of the troposphere by local convective
activity. At different altitudes the prevailing winds over each
continent funnel ozone, which is produced locally, into a massive
stagnet region over the Atlantic ocean. The combination of buring on
such a massive scale and the unique metorological conditions result in
the accumulation of ozone over the Atlantic ocean. The air flow from
southern Africa also pushes ozone into the Indian Ocean east of the
African continent and ultimately in the tropical Pacific ocean. |
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Results from the TRACE-A study, as well as other data from
the equatorial Pacific suggest that the Walker circulation plays a
major role in the ozone budget in the equatorial regions. Net ozone
production in the upper troposphere balances net ozone loss in the
lower troposphere. Mass exchange between the lower and the upper
troposphere is a result of the vertical flow associated with the
Walker circulation along the equatorial regions. Deep convection
motions over South America, southern Africa, and Oceania (rising
branches of the Walker circulation) inject nitric oxides from
combustion, soils, and lighting to the upper troposphere, driving
ozone production. Eventually, the air subsides over the oceans and net
ozone loss takes place in the lower troposphere due to low nitric
oxides concentrations and high humidifies, closing the ozone cycle. (
Jacob, et al, "Photochemistry of the Tropical Troposphere"
JGR , vol. 101, October 30, 1996, pp 24,235-24,250.)
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Curator:
NASA Official:
Last Updated 06/20/2014 |
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