Coupling of two methods to obtain pollutant emission factors from biomass burning in small combustion sources

The estimation of emissions inventories of climate forcing species and air pollutants from activities such as the burning of biomass from cooking food in rural environments in Mexico presents some degree of uncertainty due to the lack of locally obtained emission factors; emissions estimates were generally obtained with other types of biomass and cookstoves. The relevance of these pollutants to Mexico is mainly due to their contribution to air pollution, global warming and negative impacts on human health. This study presents an assembly of a series of theoretical-experimental procedures for the estimation of emission factors in improved stoves and other biomass burning processes. The design is based on the use of a controlled dilution system from which samples are obtained for the determination of PM_2.5 and the content of organic carbon and elemental carbon. The flow of diluted samples is conditioned for continuous monitoring of polluting gases (NOx, CO, NHMC, and SO₂), in addition to climate forcing gases such as CO₂ and CH₄ with a mobile laboratory equipped with instrumentation for air quality measurements. The new sampling design allows the determination of gaseous and particle matter emission factors through the application of two procedures: carbon mass balance and concentration ratios with respect to CO₂ and CO. The proposed design was evaluated for three improved cookstoves (Patsari, Onil, Ecoestufa) using a water boiling test protocol and white oak as fuel, the proposed controlled dilution sampling design can be a reliable method for the determination of emission factors from small combustion sources when biomass is used as fuel and also by using the carbon balance to obtain the emission factors, we reduce the inherent uncertainties of the process due to the difficulty associated with the sampling of this type of emissions under isokinetic conditions in low flow exhaust conditions such as those of small emission sources. The final emission factor consists of a weighted range of the factors determined for each species with respect to the amount of oxidized carbon in each of them. The feasibility of the experimental design is demonstrated by an application of using white oak wood as fuel in three improved cookstoves and one three stones. The ranges of emission factors obtained for the three improved cookstoves in g/kg of wood consumed were: CO₂, 1309-1375; CH₄, 3-4; EC, 0.16 – 0.71; OC 1.94-2.89; CO, 63 - 103; y PM_2.5, 3.17 – 4.12, while for the three stones the ranges of emission in g/kg of wood consumed were: CO₂, 1141- 1232; CH₄, 4.15-4.71; EC, 1.06 – 1.78; OC, 4.79-6.03; CO, 124 - 170; y PM_2.5, 7.47 – 10.18 g/kg.