Aerosol emissions factors from traditional biomass cookstoves in India: Insights from field measurements

Residential solid biomass cookstoves are important sources of aerosol emissions in India. Cookstove emissions rates are largely based on laboratory experiments conducted using the standard water-boiling test, but real-world emissions are often higher owing to different stove designs, fuels, and cooking methods. Constraining mass emissions factors (EFs) for prevalent cookstoves is important because they serve as inputs to bottom-up emissions inventories used to evaluate health and climate impacts. Real-world EFs were measured during winter 2015 for a traditional cookstove (chulha) burning fuel wood, agricultural residue, and dung from different regions of India. Average (±95% confidence interval) EFs for fuel wood, agricultural residue, and dung were (1) PM_2.5 mass: 10.5 (7.7-13.4) g kg^-1, 11.1 (7.7-15.5) g kg^-1, and 22.6 (14.9-32.9) g kg^-1, respectively; (2) elemental carbon (EC): 0.9 (0.6-1.4) g kg^-1, 1.6 (0.6-3.0) g kg^-1, and 1.0 (0.4-2.0) g kg^-1, respectively; and (3) organic carbon (OC): 4.9 (3.2-7.1) g kg^-1, 7.0 (3.5-12.5) g kg^-1, and 12.9 (4.2-15.01) g kg^-1, respectively. The mean (±95% confidence interval) OC= EC mass ratios were 6.5 (4.5-9.1), 7.6 (4.4-12.2), and 12.7 (6.5-23.3), respectively, with OC and EC quantified by the IMPROVE-A thermal-optical reflectance protocol. These real-world EFs are higher than those from previous laboratory-based measurements. Combustion conditions have larger effects on EFs than the fuel types. We also report the carbon mass fractions of our aerosol samples determined using the thermal-optical reflectance method. The mass fraction profiles are consistent between the three fuel categories but markedly different from those reported in past literature-including the source profiles for wood stove PM_2.5 emissions developed as inputs to receptor modeling studies conducted by the Central Pollution Control Board of India. Thermally stable OC (OC3 in the IMPROVE-A protocol) contributed nearly 50% of the total carbon mass for emissions from all fuels.