Impact of the Great China Fire of 1987 on the Tropospheric Chemistry of East Asia

Abstract

There is a growing concern that biomass burning as a consequence of anthropogenic activities has significant impact on the atmospheric chemistry, climate and on the global biogeochemical cycles. Since the late seventies, when Crutzen et al. (1979) first proposed that the emissions of trace gases from biomass burning can make an important contribution to their budgets in the atmosphere, there has been an increase in the number of research activities in parts of the world with extensive biomass burning (Andreae, 1991). It is observed that biomass burning occurs mostly in the continental tropics coinciding with the local dry season (Crutzen et al., 1985). Trace gases such as carbon monoxide (CO), methane (CH4), nitrogen oxides (NOx = NO + NO2) and non-methane hydrocarbons (NMHCs) which are emitted from the burning fires play important roles in the production of ozone, thereby impacting the tropospheric photochemical oxidant cycle. Tropospheric ozone derived from satellite data is shown to be greater than 40 Dobson Units (DU) over southern Africa and tropical south Atlantic (Fishman et al., 1990; Fishman et al., 1991). Studies on the extent of the perturbation of this biomass signal on the composition of the atmosphere have been done in the past (Fishman et al., 1993). More recently, measurements were taken during the dry season of September-October 1992 in the Transport and Atmospheric Chemistry near the Equator (TRACE) Experiment (Fishman et al. 1996). The conclusions from this activity were that the widespread biomass burning in both South America and southern Africa is the dominant source of the precursor gases responsible for the huge amounts of ozone over the South Atlantic Ocean. Efforts in understanding the spatial and vertical distribution of the trace gases emitted from biomass burning have resulted in numerous insitu field campaigns and observational data. Measurements techniques such as satellite remote sensing, radiosondes and aircraft measurements are commonly being used to probe the atmosphere. On the other hand, synoptic-scale modeling of the influence of the fires on the atmosphere has been minimal, with the majority of work done in modeling the convective transport and redistribution of biomass burning emissions (Crutzen and Carmichael, 1993; Pickering et. al, 1996; Chatfield et. al, 1996).