Mixing State of Carbonaceous Aerosols of Primary Emissions from “Improved” African Cookstoves

Abstract

Designs of "improved" stoves are introduced recently to benefit the solid fuel consumption of cooking activities in developing countries, but the uncertainties concerning the combustion processes and particulate emissions remain poorly characterized. To help understand this, combustion in three examples of "improved" African cookstoves was investigated in the laboratory. A typical European heating stove was included for comparison purpose. Detailed aerosol emissions were studied in real-time with an Aerosol Mass Spectrometer and Single Particle Soot Photometer, to explore interactions between black carbon (BC) and organic carbon aerosols, which were parametrized according to modified combustion efficiency (MCE), a common metric used within the atmospheric emission community. Greater than 50% of the total organic matter (OM) was found in BC-containing particles when MCE was >0.95 for dry oak and coal fuels, whereas at lower MCE, over 80% of the total OM for most of the fuels existed in particles without detectable BC. When the OM mass fraction of total particulate matter (PM) > 0.9, the mass ratio of OM to refractory BC in BC-containing particles was about 2-3, but only ∼0.8 when OM mass fraction <0.9. These findings are not currently included in models and such information should be considered in the future emission scenarios.

Pollutant Emissions from Improved Cookstoves of the Type Used in Sub-Saharan Africa

“…The wall temperature of the firebox did not rise above 100°C during the experiments so wall radiation is negligible. The firebox provides a near-symmetrical inflow of air through 130 mm high inlets around the base providing combustion and dilution air as previously described in Ting et al (2018). A chimney section, 1 m high and 125 mm in diameter at the centre of the top of the fire-box, was used for sampling of the combustion products and the gas velocity was measured using a S-type pitot tube (these were in the range 1.0 to 4.5 m/s).…”

“…The distance of the inlet to the dilution tunnel from the firebox chimney is such that it has no influence on the extraction of the combustion products; the behaviour of the flames above the cookstoves is dominated by buoyancy effects. Diluted combustion products were sampled from the firebox chimney, and additionally diluted combustion products were sampled from the dilution tunnel, as previously described (Ting et al, 2018). The exhaust gas composition in the firebox chimney was measured using a Gasmet DX-4000 Fourier Transform Infrared (FTIR) spectrometer; measurements in the dilution tunnel were made using a Testo 340 analyser.…”

“…The sub-micron non-refractory aerosol concentrations were measured with an Aerodyne compact Time-of-Flight Aerosol Mass Spectrometer, cToF-AMS. Online measurement of refractory black carbon (rBC) particles was performed using a Single Particle soot photometer (SP2, (Droplet Measurement Technologies Inc.); here only the ratio of rBC to rBC plus OM (organic matter) is given; other results are given in Ting et al (2018).…”

Lifecycle of light-absorbing carbonaceous aerosols in the atmosphere

“…MCE is defined as the net emitted CO 2 from the sources (relative to background) over the total net emitted carbon oxide (CO 2 + CO) 7 . A higher MCE (typically > 0.95) 8,9 denotes the high-temperature flaming phase, while a lower MCE is associated with smoldering, less efficient burning.…”

Examination of Combustion-Generated Smoke Particles from Biomass at Source: Relation to Atmospheric Light Absorption

“…These show that soot samples produced for both flaming and smouldering combustion are not significantly different in any respect. Particle size studies (e.g Ting et al, 2018). have shown that are 20 nm and 100 nm particles present in a bi-modal distribution in biomass combustion.…”