A review of the physicochemical characteristics of ultrafine particle emissions from domestic solid fuel combustion during cooking and heating

Residential solid fuel combustion has increased because of rising energy costs but little is known about the emission characteristics of unregulated pollutants such as ultrafine particles (UFPs). This review aims to characterise the emis-sions and chemical composition of UFPs, build an understanding of the particle number size distribution (PSD), as-sesses the factors affecting pollutants emission, and the efficacy of pollutants mitigation strategies. A systematic appraisal of literature suggests that the pollutants emissions from domestic solid fuel combustion are influenced by the quality and type of fuels, stove types, and combustion conditions. Low volatile matter content fuels such as smoke-less fuels emit lesser PM2.5, NOX, SO2 than high volatile matter content fuels such as wood. However, CO emissions does not directly correlate with volatile matter content, but depend on air supply, combustion temperature, and fuel particle size. Majority of UFPs are emitted during the coking and flaming phases of combustion. Since UFPs have a large surface area, they adsorb significant amounts of hazardous metals and chemicals such as PAHs, As, Pb, and NO3 in addition to minor amounts of C, Ca and Fe. Emission factor of solid fuel based on the particle number concen-tration (PNC) can range from 0.2 to 2 x 1015 # kg-1 of fuel. UFPs were not found to be reduced by improved stoves, mineral additives, or small-scale electrostatic precipitators (ESP). In fact, improved cook stoves were found to increase UFP emissions by a factor of 2 compared with conventional stoves. However, they have demonstrated a 35-66 % re-duction in PM2.5 emissions. Using a domestic stove within a home puts occupants at risk of being exposed to significant concentrations of UFPs in a short period of time. As there are limited studies on the topic area, further research on dif-ferent improved heating stoves is required to better understand their emissions of unregulated pollutants such as the UFPs.