Molecular Composition of Particulate Matter Emissions from Dung and Brushwood Burning Household Cookstoves in Haryana, India

Abstract. Emissions of airborne particles from biomass-burning are a significant source of black carbon (BC) and brown carbon (BrC) in rural areas of developing countries where biomass is the predominant energy source for cooking and heating. This study explores the molecular composition of organic particles from household cooking emissions, with a focus on identifying fuel-specific compounds and BrC chromophores. Traditional meals were prepared by a local cook with dung and brushwood-fueled cookstoves in a village of Palwal district, Haryana, India. The cooking events were carried out in a village kitchen while controlling for variables including stove type, fuel moisture content, and meal. The particulate matter (PM2.5) emissions were collected on filters, and then analyzed via nanospray desorption electrospray ionization/high resolution mass spectrometry (nano-DESI-HRMS) and high performance liquid chromatography/photodiode array/high resolution mass spectrometry (HPLC-PDA-HRMS) techniques. The nano-DESI-HRMS analysis provided an inventory of compounds present in the particle phase. Although several compounds observed in this study have been previously characterized using gas chromatography methods, a majority of species in nano-DESI spectra were newly observed biomass-burning compounds. Both the stove (chulha or angithi) and the fuel (brushwood or dung) affected the composition of organic particles. The geometric mean PM2.5 emissions factor and the molecular complexity of PM2.5 emissions increased in the following order: brushwood/chulha (4.9 ± 1.7 g kg-1 dry fuel, 93 compounds), dung/chulha (12.3 ± 2.5 g kg-1 dry fuel, 212 compounds), and dung/angithi (16.7 ± 6.7 g kg-1 dry fuel, 262 compounds). The lower limit for the mass absorption coefficient (MAC) at 365 nm and 405 nm for brushwood PM2.5 was 3.4 m2 g-1 and 1.8 m2 g-1, respectively, which was approximately a factor of two higher than that for dung PM2.5. The HPLC-PDA-HRMS analysis showed that, regardless of fuel type, the main chromophores were CxHyOz lignin fragments. The main chromophores accounting for the higher MAC values of brushwood PM2.5 were C8H10O3 (tentatively assigned syringol), possible nitrophenol species C8H9NO4, and C10H10O3 (tentatively assigned methoxycinnamic acid).