EFFECTS OF TROPICAL DEFORESTATION ON GLOBAL AND REGIONAL ATMOSPHERIC CHEMISTRY MICHAEL KELLER National Center for Atmospheric Research, RO. Box 3000, Boulder, CO 80307, U.S.A. DANIEL J. JACOB Earth and Planetary Sciences, Division of Applied Sciences, Harvard University, Cambridge, MA 02138, US.A. STEVEN C. WOFSY Earth and Planetary Sciences, Division of Applied Sciences, Harvard University, Cambridge, MA 02138, US.A. and ROBERT C. HARRISS Center for the Study of Earth, Ocean, and Space, Science and Engineering Building, University of New Hampshire, Durham, NH 03824, U.S.A. Abstract. A major portion of tropospheric photochemistry occurs in the tropics. Deforestation, colonization, and development of tropical rain forest areas could provoke significant changes in emissions of radiatively and photochemically active trace gases. A brief review of studies on trace-gas emissions in pristine and dis- turbed tropical habitats is followed by an effort to model regional tropospheric chemistry under undisturbed and polluted conditions. Model results suggest that changing emissions could stimulate photochemistry leading to enhanced ozone production and greater mineral acidity in rainfall in colonized agricultural regions. Model results agree with measurements made during the NASA ABLE missions. Under agricultural/pastoral development scenarios, tropical rain forest regions could export greater levels of N20 , CH4, CO, and photochemical precursors of NOy and 03 to the global atmosphere with implications for climatic warming. 1. Introduction Important changes in regional and global atmospheric chemistry may be associated with deforestation and with agricultural or industrial development in tropical forest regions. A major fraction of global atmospheric photochemistry occurs in the tropics (Logan et al., 1981; Crutzen, 1987). Changes in photochemical processes in the tropics may disturb global balances for important gases such as CO or 03 . Tropical soils and vegetation represent globally significant sources of reactive hydrocarbons and CO (Crutzen and Gidel, 1983; Logan, 1985), NO, N20 (Keller et al., 1983, 1986; Seiler and Conrad, 1987; Kaplan et al., 1988; Goreau and de Mello, 1987; Johansson et al., 1988), and CH 4 (Bartlett et al., 1988). Disturbance of vegetation and soils can alter emission rates for these important gases. Goreau and de Mello (1988) have discussed some possible implications of tropical defores- tation for the greenhouse gases CO2, CH4, and N20. Climatic Change 19: 139-158, 1991. 9 1991 KluwerAcademic Publishers. Printed in the Netherlands.