Differences in chemical composition of PM_2.5 emissions from traditional versus advanced combustion (semi-gasifier)...

A common strategy to improve indoor air quality in households burning coal and biomass is the introduction of advanced combustion solid fuel stoves, which can use existing fuels yet emit fewer pollutants. Chemical composition of PM is affected by numerous combustion parameters, but is often not considered in energy transitions, despite varying toxicity among chemical components. We analyzed PM_2.5 emissions from combustion of solid fuels (coal, wood, and straw; whole and pelletized) in a variety of stoves (cookstoves and heating stoves; traditional and semi-gasifier, including forced versus natural draft and fixed versus reciprocating grate). To assess the effects of fuel and stove type on PM_2.5 composition, we measured elemental carbon (EC), organic carbon (OC), water-soluble OC, water-soluble inorganic ions (e.g. SO₄^2-, Cl^-, K⁺), and organic molecular markers. PM_2.5 emissions from traditional stoves were mostly carbonaceous: 76-90% organic matter (OM), 5-6% EC, and less than 2% inorganic ions. In contrast, semi-gasifier stoves emitted more inorganic PM_2.5: on average, ions comprised 65%, 9% was OM, and 4% was EC. Within the semi-gasifier cookstoves, forced-draft cookstove emissions had lower OM (1-3%) and higher ion concentrations (84-88%) than the natural-draft cookstove (5-14% OM, 30-83% ions). Levoglucosan was detected in PM_2.5 from combustion of wood in the traditional cookstove and biomass pellets in the natural-draft semi-gasifier cookstove, but not from wood pellets in the forced-draft semi-gasifier cookstove. Across a range of different fuels and stoves, stove type influenced emitted PM composition more than fuel type, underscoring the impact of combustion conditions on PM chemical composition.