View full article: PDF (81980515 bytes)

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 101, NO. D19, PAGES 24,279–24,306, 1996

A general model of how fire emissions and chemistry produce African/oceanic plumes (O₃, CO, PAN, smoke) in TRACE A

Robert B. Chatfield

NASA Ames Research Center, Moffen Field, California

John A. Vastano

San Jose State University, San Jose, California

H. B. Singh

NASA Ames Research Center, Moffen Field, California

G. Sachse

NASA Langley Research Center, Hampton, Virginia

Abstract

A full‐chemistry simulation of the Great African Plume gives one example of a broad conceptual model of the intercontinental pollution of the tropical middle troposphere by lofted biomass burning plumes. This two‐dimensional idealization ‘‘calibrated’’ by carbon monoxide distributions links conventional estimates of burning emissions to oceanic concentrations of pollutants. This paper makes use of GRACES, a modular photochemical simulation system, in two forms. The results of the chemically intensive two‐dimensional form, using idealized winds, mixing, deposition, and rainout, match the general concentration patterns of a three‐dimensional GRACES model study of CO during the TRACE A/SAFARI period of October 1992 (reported separately). The study highlights the importance of simulating the vertical and diurnal variation of the planetary boundary layer and cloud activity. These correlate temporally with the intensity of tropical agricultural burning. We emphasize one situation, the drift northward and eastward of pollution into the interocean convergence region, where it rises by small‐scale motions and rides out westward in the lower midtroposphere (<5 km). These effects help set in place large strata of enhanced CO, ozone, and other pollution over the equatorial Atlantic Ocean. Overall, our comparisons of simulations with the TRACE A data on the cycling of CO, NO_x, and O₃ in the tropical atmosphere suggest substantial agreement of current emission estimates and atmospheric concentrations. In certain regions, ozone is simulated slightly below observed levels. The striking major disagreements are in NO_y (total reactive nitrogen) and HNO₃, which are intimately related to CO and O₃; this suggests that current theory omits at least one fundamental process. © American Geophysical Union 1996

Index Terms: 0399 Atmospheric Composition and Structure: General or miscellaneous.

View full article: PDF (81980515 bytes)

Citation: Chatfield, R., J. Vastano, H. Singh, and G. Sachse, A general model of how fire emissions and chemistry produce African/oceanic plumes (O3, CO, PAN, smoke) in TRACE A, J. Geophys. Res., 101(D19), 24,279–24,306, 1996.

Copyright 1996 by the American Geophysical Union.