Distribution of NMHC ratios in the Pacific during PEM-West B and PEM-Tropics A

Abstract

Under the auspices of NASA's Global Tropospheric Experiment (GTE), the Pacific Exploratory Missions (PEM) have collected numerous air samples of many regions of the troposphere. Data from PEM-West B (February 7 to March 15, 1994), and PEM-Tropics A (August 15 to October 5, 1996) have been used here to study non-methane hydrocarbon (NMHC) ratios and to compare pollution transport by large scale convection and subsidence, as well as horizontal transport across the Pacific. For PEM-Tropics A, 7 cases are studied, each involving different aspects of transport. Persistent circulation features in the South Pacific played a significant role in NIMHC ratio distribution and processing. For PEM-West B, sources of a large pollution region are studied and compared to equatorial transport. NMHC ratios were found to be useful tracers of pollution distribution through the troposphere. The contrasts of these ratios across relatively small distances, particularly on either side of the South Pacific Convergence Zone in PEM-Tropics A, suggest that convection shapes pollution transport and distribution, particularly in the South Pacific.