Impact of carbonized products on reducing pollutant emission from household solid fuel combustion

Household solid fuel combustion remains a major source of ambient air pollution in developing regions. To address this challenge, we propose a carbonization-driven modification strategy by converting low-rank coal and agricultural straw into bio-coal briquettes through volatile removal. Systematic field measurements using a dilution sampling system revealed that stable combustion of carbonized briquettes in semi-gasifier stoves significantly reduced particulate emissions. Specifically, the optimal blend containing 20 % carbonized straw achieved a 41.5 % decrease in PM_2.5 emission factor (3.7 vs. 4.9 mg/g) compared to raw coal, along with the lowest total suspended particulates (TSP, 3.92 mg/g) and PM₁ (2.14 mg/g). Mass-based emission reductions were observed for organic carbon (88.4 ± 1.8 %), elemental carbon (88.8 ± 2.5 %), 16 priority PAHs (85 ± 1.6 %), and benzopyrene (95 ± 2.7 %), while energy-based emission factors of heavy metals and toxic nonmetals (Pb, Cr, As, etc.) decreased by 13.95 %. SEM-verified particle morphology indicated compact carbon matrices with fewer fragmented particulates. Crucially, this technology demonstrates dual benefits: a reduction in toxicity equivalency of inhalable pollutants per household annually, and decentralized production feasibility using rural biomass waste. Despite higher particulate emissions during straw carbonization than coal (21.7 vs. 12.1 mg/g), the net emission reduction across the fuel lifecycle positions carbonized briquettes as a scalable transition solution toward low-emission household energy in resource-limited settings.