TRACE-P
OH and HO2 measurements with the Airborne Tropospheric
Hydrogen Oxides Sensor (ATHOS) on the
DC-8
Principal
Investigator: William H. Brune, Pennsylvania State University,
University Park, PA
Co-Investigators: Monica Martinez-Harder, Hartwig Harder
The
Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) measures
OH and HO2 from the NASA DC-8. This instrument detects
OH by laser induced fluorescence (LIF) in detection chambers
at low pressure and detects HO2 by chemical conversion
with NO followed by LIF detection. The demonstrated detection
limit (S/N=2, 5 min.) for OH is about 0.005 pptv (1X105 cm-3 at
2 km altitude) and for HO2 is 0.05 pptv (1X106 cm-3 at 2 km altitude). We will use ATHOS to measure
OH, HO2, and HO2/OH during TRACE-P, analyze
these results by comparing them against fundamental relationships
and computer models, and publish the analyses. As participants
in a tower-based study this summer, we are developing an attachment
to ATHOS to detect RO2+ HO2-. It
may be tested well enough to include as an attachment for TRACE-P. TRACE-P
HO, measurements will help develop a clearer picture of the atmospheric
oxidation and O3 production
that occur as Asian pollution spreads across the Pacific Ocean.
We
anticipate both new results and confirmation of previous results.
Besides contributing to the science goals outlined in the TRACE-P
NRA, HOx, measurements will be combined with simultaneous
measurements of environmental factors and other chemical species
to test the following hypotheses:
Testing
these hypotheses relies heavily on the simultaneous measurements
of HOx, all the chemical species that interact with
HOx, and the environmental conditions, particularly
the photolysis frequencies. It is important to obtain this entire
measurement suite from the planetary boundary layer to the ceiling
of the DC-8 at 12 km, as well as in the presence of clouds and
heavy pollution nearer the Asian coast. Measurements while flying
out of and into airports are important photochemical kinetics
tests because of the different amounts of NO that are mixed into
the continental air. In addition, measurements must be made at
different times of the day and night.
TRACE-P
will add to a growing body of HO. data that we have collected
with ATHOS and GTHOS, the towered-based configuration of ATHOS
that we use for near-surface studies. ATHOS has participated
in SUCCESS (1996), SONEX (1997), PEM Tropics B (1999), and SOLVE
(1999-2000). GTHOS has participated in PROPHET, at a semi-rural
heavily forested site in northern lower Michigan in summer, 1998
and in Nashville SOS, in the urban plume of Nashville in summer,
1999. These measurements are giving us a view of HO. photochemistry
for a wide range of HOx sources, NOx levels,
and hydrocarbon loadings. TRACE-P allows us to sample the influence
of urban-level, processed pollution on a low-hydrocarbon, pristine
environment, a condition that we have not previously studied
extensively.
An
exciting aspect of TRACE-P is the connection between the aircraft
and satellite observations. While instruments on the Terra and
ENVISAT satellites cannot measure OH and HO2, they
can measure chemical species that have great influence on HOx,
such as CO, O3, and
NO2 (a measure of NO). By comparing the satellite
and aircraft measurements for a wide range of environments, we
should be able to construct parameterizations of atmospheric
oxidation and ozone production.
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