Emissions of greenhouse gases and other airborne pollutants from charcoal making in Kenya and Brazil

Abstract

Airborne emissions from charcoal-making kilns commonly used in Kenya and Brazil were measured during typical operating conditions. Emission factors were determined for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), carbon monoxide (CO), total nonmethane hydrocarbons, nitrogen oxides (NOx) and total suspended particulates (TSP) along with charcoal production efficiency and charcoal and fuelwood carbon and energy contents. The conversion of wood carbon to charcoal carbon ranged from 37 to 69%, depending on kiln type. Emission factors, expressed as grams of pollutant per kilogram of charcoal produced, for the eight kilns ranged from 543 to 3027 for CO2, 32–62 for CH4, 143–373 for CO, 24–124 for total nonmethane organic compounds, 0.011–0.30 for N2O, 0.0054–0.13 for NOx, and 13–41 for TSP. On average, fuelwood carbon was approximately diverted as follows: 51% to charcoal, 27% to CO2, and 13% to products of incomplete combustion (PIC). Due to the higher global warming potentials (GWPs) of PIC relative to CO2 on a carbon atom basis, such kilns can produce rather large net greenhouse gas emissions, even when the wood is harvested renewably. Based on published GWPs for CO2, CH4, and N2O only, we estimate that 0.77–1.63 kg C-CO2 (carbon as carbon dioxide equivalents) is emitted per kilogram of charcoal produced. We estimate that the total primary global warming commitment (GWC) of Kenyan and Brazilian charcoal-making kiln emissions is about 2.7 and 7.5 million tons (Mt) C-CO2, respectively. For comparison, the primary GWC from fossil fuel use in the United States is almost 1700 Mt C-CO2.