Introduction

Deforestation in the tropics plays an important role in releasing large amounts of C02 into the atmosphere (Seiler and Crutzen, 1980; Crutzen et al, 1989). Biomass burning is also a significant source of chemically active trace gases (e.g., CO,CH4, non-methane hydrocarbons, NOx) leading to the photochemical production of tropospheric ozone (Crutzen et al., 1979). Satellite, aircraft and ground based measurements have identified plumes of elevated tropospheric ozone concentration emanating from South America and Africa during the biomass burning season (Fishman et al., 1991; Andreae et al., 1992; Thompson et al., 1996; Blake et al., 1999).

In 1997, unprecedented widespread fires occurred in Indonesia, starting in June-July and lasting for several months. Most of the fires were set by land owners, commercial loggers and small farmers in attempts to clear and cultivate the land. However, the severe drought induced by a strong El NiƱo Southern Oscillation event exacerbated the fires and smoke and haze. As a result of the release of significant amount of trace gases and particles, these fires profoundly affected the chemical composition of the troposphere on a regional scale. In particular, tropical tropospheric ozone maps from the Earth-Probe/TOMS instrument indicate an increase from about 40 Dobson Units (DU) in October 1996 to about 60-70 DU in October 1997 over the Indonesian area (Hudson and Thompson, 1998).

In this paper, we use a global three-dimensional chemical transport model, called MOZART, to investigate the sensitivity of the calculated distribution of tropospheric ozone and its precursors to estimated biomass burning emissions associated with the 1997 Indonesian fires. The calculations are aimed mainly at testing the ability of a state-of-the-art global tropospheric chemical transport model to reproduce the effects of biomass burning emissions on ozone in the troposphere. A brief description of the model is provided in section 2. The emission scenarios and the model simulations are described in section 3, and the results are discussed in section 4. Concluding remarks are given in section 5.

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