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Exploratory study of Polycyclic Aromatic Hydrocarbon (PAH) contributions to household air pollution arising from improved cookstove use in rural Malawi

Around three million premature deaths annually are ascribed to household air pollution (HAP) arising from inefficient burning of biomass and emissions of products of incomplete combustion. The developing-world response has been widespread adoption of improved cookstove (ICS) technologies. This exploratory study evaluates variation in polycyclic aromatic hydrocarbon (PAH) attached to inhalable particulate matter (PM) in rural Malawi households adopting ICS use. PM literature supports HAP exposure to inhalable PM is lowered, albeit variably, compared to traditional fires, but remains significant. Similar is expected for PAH; however, datasets lack discerning PAH chemical-specific contributions to risks. The study introduces the Malawian context, invokes a PAH reconnaissance approach sampling kitchen soot ‘spots’ and residential dusts, and relates PAH occurrence to the two sample types collected and ICS types surveyed. The total PAH for dusts was low (c. 2 μg/g mean), with volatile 2-ring naphthalene dominant. Soot total PAH was much higher (c. 200 μg/g mean to a maximum of 815 μg/g). Soot from PM emissions poses a major primary health concern. Despite PAH trends not being obvious with ICS type (limited sample size) and the wide range in soot total PAH, soot PAH-fingerprints were well constrained with low variation of diagnostic PAH ratios, exhibiting n-ring fingerprints close to the soot median (0.1% 2-ring, 20% 3-ring, 61% 4-ring, 14% 5-ring, 5% 6-ring PAH). These corroborate the expected wood-related combustions sources, but also point to the needs to understand factors that control wide variations in PM and (total) PAH emitted as these control variations in HAP and differing risks posed to individual households. Further household-based research is thus recommended discerning relationships between PM emissions and PAH contents, driving the chemical-composition health risks. These should establish influences on PAH exposure arising from ICS type/model selected, operational modes, building/ventilation conditions, variable fuel sources and non-optimal ICS use. 
 
   
 
 Key words: Improved cookstoves (ICS), polycyclic aromatic hydrocarbon (PAH), household air pollution (HAP), particulate matter (PM), Malawi, indoor air pollution (IAP).