Chemical Characterisation and Oxidative Potential of Aerosols Emitted From Solid Biomass Fuels Use in Rural India

The use of biomass fuels as primary source for cooking still persists on large scale in several parts of rural India. Dependence on biomass fuels for cooking and heating activities exposes people, especially women and infants in their care, to high levels of household air pollutants, ultimately leading to adverse health effects. The health effects may be mediated by oxidative potential (OP) of PM, however, the PM components responsible for its OP or ability to generate reactive oxygen species are poorly understood.

In this study, field measurements were made to collect PM_2.5 emitted from burning of biomass fuels and different igniters (e.g. plastic, cloth, paper), on filter substrates, using a multi-stream sampler (flow rate 20.2 L/min) during cooking sessions in 8 households from rural Maharashtra, India. Biomass fuels were burned in traditional stove type, to cook typical meals of rice/chapattis during cooking sessions which typically lasted 40-90 min. The collected PM_2.5 samples were subsequently analysed for organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC) and oxidative potential by acellular DTT (Dithiothreitol) assay.

The average mass concentration during cooking using crop residues, firewood, and mixed biomass fuels were 3120±2212 μgm^-3, 400 ± 17μgm^-3, 460 ±180μgm^-3, respectively. The average OC and EC levels were 1184±1085, 643±518 μgm^-3 (crop residues), 178±102, 75±71 μgm^-3 (firewood), 186±73, 154±138 μgm^-3 (mixed biomass fuels), respectively. The outdoor PM_2.5, OC and EC levels in the village were 80±6, 45±42, 10±7μgm^-3, respectively. The corresponding WSOC levels were 54%, 57%, and 60% of OC for the three cooking fuel categories, respectively , while in ambient it was found to be 30% of the OC.

The corresponding volume normalised DTT activity (DTTv) was 21±7nmol min^-1 m^-3 for crop residues, 30±8nmol min^-1 m^-3 for firewood and 23±8nmol min^-1 m^-3 for mixed biomass fuels while the DTTv for ambient PM was (1±0.6nmol min^-1 m^-3) an order of magnitude less redox active than biomass fuel samples. Thus, suggesting that the exposure to PM from biomass cooking may pose substantial risk to a large population using these cooking fuels in rural areas.

Our first results suggest that cooking with crop residues lead to significantly higher emissions and indoor exposures to PM_2.5 and its carbonaceous components however the volume normalised OP was found higher for firewood. Further correlations and assessment of contribution of chemical constituents to the oxidative potential will be discussed.