NO_x emissions from biomass burning of shifting cultivation areas from tropical deciduous forests of India – estimates from ground-based measurements

Abstract

Biomass burning in the tropics is an important source of trace gases. Shifting cultivation in India is one of the major sources of biomass burning activities, during which due to combustion, several trace gases are emitted into the atmosphere. NO_x emissions are relatively important as they affect the tropospheric photochemistry. In the present study, an attempt has been made to quantify the NO_x emissions from shifting cultivation areas of tropical dry deciduous forests of India, at two sites. Fuel load, fuel characteristics, and nutrients with respect to carbon and nitrogen have been analyzed. Emission ratios have been calculated relative to CO₂. Results of the study suggested that fuel load ranged from 12–15.3 t ha^-1. Fire intensity at the first site was 3207 kcal s^-1 m^-1 and 2882 kcal s^-1 m^-1 at the second site. The differences in the fuel moisture were found to be less than 10% at both of the sites. The CO/CO₂ ratio at the two sites did not vary much due to the low variation in moisture content. The carbon and nitrogen loads for the two sites ranged from 5603 t C ha^-1 to 286 t N ha^-1 and 6364 t C ha^-1 and 239 N ha^-1, respectively. Using the relation of estimating the emission factor (EF) for estimating the NO_x emissions (EF (NO_x)=-1.5+3.9_nf, where, (r=0.95) EF(NO_x) is the emission factor for NO_x in grams of nitrogen per kilogram of dry matter (g N kg^-1 dm) burned and 'nf' is the percent of nitrogen bound within the plant matter, for tropical deciduous forests, suggests an emission rate of 7.0 (g N kg^-1 dm) for the first site, and 4.7 (g N kg^-1 dm) for the second site when compared to actual measured emission rates of 4.8 (g N kg^-1 dm) for the first site and 3.5 (g N kg^-1 dm) for the second site, indicating a higher estimate for the global regression relation used by Dignon and Penner. The emission factors computed from nitrogen content of the fuel material for tropical dry deciduous forests are nearer to the relation obtained for African Savanna fires. Comparison of the measured emission factors for the tropical deciduous forests with other ecosystems has been made in the paper.