To assess emissions from these fire practices a few groups have investigated both consumption of biofuels and related emissions. Like the group of J.-P. Lacaux, Toulouse, France, we have studied patterns of biofuel use and made measurements of emissions of CO₂, CO, NO and occasionally organic compounds and aerosols in the lodgings of rural and urban Zimbabwe, Nigeria and Kenya.

Figure 1. The statistical distribution of the time integrated ratios DCO/DCO2 observed during domestic combustion of different biofuels at several locations in Zimbabwe and Nigeria.

Figure 2. The statistical distribution of the time integrated ratios DNO/DCO2 observed during domestic combustion of different biofuels at several locations in Zimbabwe and Nigeria.

Figures 1 and 2 show DCO/DCO₂ and DNO/DCO2 ratios obtained in Zimbabwe and Nigeria during the field phases of 1995 and 1996 (Ludwig et al., to be submitted). As the fuel mass consumed was determined as well, it was possible to quantify emissions from the domestic sources. Additionally, we collected information on biofuel consumption, which is compared to literature values in Table 1. We have to distinguish between urban and rural consumption rates as they differ considerably. Together with population statistics and the emission figures, we thus were able to assess the CO₂, CO and NO emissions from domestic combustion processes. Results for Zimbabwe are compared to other sources in Table 2. It turns out, that for average fuel consumption rates CO₂ dominantly stems from domestic cooking practices, whereas for NO the emissions from soil and industrial processes are more important. We realize that such proportions of the different sources vary from region to region.

Table 1. Fuelwod consumption rate estimates for Zimbabwe by different authors (taken from Marufu et al., to be submitted).   Fuelwood comsumption rate estimates Mg capita—1 year—1 Literature source urban rural Hosier et al., 1986 0.1 1.1 Attwell et al., 1989 0.1 — Grundy et al., 1993 — 1.4 Campbell and Mangono, 1994 0.3 0.81 Hemstock and Hall, 1995 — 1.2 Marufu et al., 1997a 0.56 0.95 Marufu et al., b 0.4 1.3

Table 2. Comparison of CO2, CO, and NO emissions from different sources for Zimbabwe (taken from Marufu et al., to be submitted). Source Emission   CO2 Tg C yr—1 CO Tg C yr—1 NO Tg C yr—1 Domestic biomass burning 4.6 0.44 5.27 Savanna burning 2.0 0.11 8.9 Biogenic emission (soil) — — 22.2 Coal (industry) 3.8 0.001 21.6 Liquid fuels (transportation) 0.8 0.11 12.0

A tentative global analysis shows that the source strength of domestic biomass burning is on the order of 1500 Tg CO₂-C yr^-1, 140 Tg CO-C yr^-1, and 2.5 Tg NO-N yr^-1. This represents contributions of about 7 to 20% to the global budgets of these gases (Ludwig et al., to be submitted).

Results of our work are published or are in the process of preparation for publication.

References

1. L. Marufu, J. Ludwig, M.O. Andreae, F.X. Meixner and G. Helas (a), Domestic biomass burning in rural and urban Zimbabwe-Part A, Biomass and Bioenergy, 12, 53-68, 1997.
2. L. Marufu, J. Ludwig, M.O. Andreae, J. Lelieveld and G. Helas (b), Spatial and temporal variation in domestic biofuel consumption rates and patterns in Zimbabwe: Implications for atmospheric trace gas emission - Part B, submitted to Biomass and Bioenergy.
3. E. Kituyi, L.T. Marufu, S.O. Wandiga, I.O. Jumba, M.O. Andreae and G. Helas (a), Species preference patterns and sustainability of biofuel resources in Kenya, submitted to Ambio.
4. E. Kituyi, L.T. Marufu, B. Huber, S.O. Wandiga, I.O. Jumba, M.O. Andreae and G. Helas (b), Biofuel consumption rates and patterns in Kenya, submitted to The Kenya National Academy of Sciences Journal.
5. E. Kituyi, L.T. Marufu, S.O. Wandiga, I.O. Jumba, M.O. Andreae and G. Helas (c), Emissions of CO and NO from domestic biomass fires in Kenya, to be submitted.
6. J. Ludwig, L.T. Marufu, B. Huber, M.O. Andreae and G. Helas, Combustion of biomass fuels in developing countries: A major source of atmospheric pollutants, to be submitted.