Pacific Exploratory Mission in the tropical Pacific: PEM-Tropics A, August-September 1996

The NASA Pacific Exploratory Mission to the Pacific tropics (PEM-Tropics) i s the third major field campaign of NASA's Global Tropospheric Experiment ( GTE) to Study the impact of human and natural processes on the chemistry of the troposphere over the Pacific basin. The first two campaigns, PEM-West A and B were conducted over the northwestern regions of the Pacific and foc used on the impact of emissions from the Asian continent. The broad objecti ves of PEM-Tropics included improving our understanding of the oxidizing po wer of the tropical atmosphere as well as investigating oceanic sulfur comp ounds and their conversion to aerosols. Phase A of the PEM-Tropics program, conducted between August-September 1996, involved the NASA. DC-8 and P-3B aircraft. Phase B of this program is scheduled for March/April 1999. During PEM-Tropics A, the flight tracks of the two aircraft extended zonally acro ss the entire Pacific Basin and meridionally from Hawaii to south of New Ze aland. Both aircraft were instrumented for airborne measurements of trace g ases and aerosols and meteorological parameters. The DC-8, given its long-r ange and high-altitude capabilities coupled with the lidar instrument in it s payload, focused on transport issues and ozone photochemistry, while the P-3B, with its sulfur-oriented instrument payload and more limited range, f ocused on detailed sulfur process studies. Among its accomplishments, the P EM-Tropics A field campaign has provided a unique set of atmospheric measur ements in a heretofore data sparse region; demonstrated the capability of s everal new or improved instruments for measuring OH, H2SO4, NO, NO2, and ac tinic fluxes; and conducted experiments which tested our understanding of H Ox and NOx photochemistry, as well as sulfur oxidation and aerosol formatio n processes. In addition, PEM-Tropics A documented for the first time the c onsiderable and widespread influence of biomass burning pollution over the South Pacific, and identified the South Pacific Convergence Zone as a major barrier for atmospheric transport in the southern hemisphere.