Pacific Exploratory Mission in the Tropical Pacific

Project Description
Abstract:


The Pacific Exploratory Mission - Tropics B (PEM-Tropics B) was
conducted by the NASA Global Tropospheric Experiment (GTE) over
the tropical Pacific Ocean in March-April 1999. It used two
NASA aircraft, a DC-8 and a P-3B. Its central objective was to
improve knowledge of the factors controlling ozone, OH,
aerosols, and related species over the vast and remote region
defined by the tropical Pacific. Both aircraft were equipped
with extensive instrumentation for measuring numerous chemical
compounds and gases. The geographical coverage ranged from 38N
to 36S in latitude and 148W to 76E in longitude. Major
deployment sites included Hilo, Hawaii; Christmas Island;
Tahiti; Fiji; and Easter Island. PEM-Tropics B was a sequel to
PEM-Tropics A, conducted in September-October 1996. The latter
field study encountered considerable biomass burning indluence
over the South Pacific associated with the dry season in the
southern tropics. PEM-Tropics B, conducted in the wet season of
the so! uthern tropics, observed an exceedingly clean
atmosphere over the South Pacific but a variety of pollution
influences over the tropical North Pacific, including
long-range transport from industrial sources in Eurasia and
North America as well as from seasonal biomass burning in
Southeast Asia. Photochemical ozone loss over both the North
and the South Pacific exceeded local photochemical production
by about a factor of two, implying the need for a major inflow
term to balance the tropospheric budget over the
region. Dedicated flights investigated the sharp air mass
transitions at the Intertropical Convergence Zone (ITCZ) and at
the South Pacific Convergence Zone (SPCZ). Extensive OH
observations, many involving diurnal profiles at several
different altitudes, permitted the first large-scale
comparisons with photochemical model predictions. High
concentrations of oxygenated organics were observed
ubiquitously in the tropical Pacific atmosphere and may have
important implicat! ions for global HOx and NOx
budgets. Extensive equatorial measurements of DSMS and OH, some
of which were recorded in coincidence with exceptionally high
levels of the oxidation product DMSO, suggest that important
aspects of marine sulfur chemistry are also still poorly
understood.

Provided by:

Raper, J.L., M.M. Kleb, D.J. Jacob, D.D. Davis, R.E. Newell,
H.E. Fuelberg, R.J. Bendura, J.M. Hoell, and R.J. McNeal