Significant reduction in air pollutant emissions from household cooking stoves by replacing raw solid fuels with their carbonized products

Abstract

Residential solid fuel combustion contributes significantly to ambient and indoor air pollutions. An appropriate clean solid fuel to reduce residential emissions is urgently needed. This study evaluates the reduction in pollutant emissions achieved by carbonized solid fuels in residential cooking practice. Four biochar samples, three semi-coke briquette samples and their raw materials were tested in a typical cooking stove. These carbonized samples showed higher thermal efficiencies and lower particulate matter (PM) emission factors (EFs) than their raw material samples. Owing to distilled volatile matter during carbonization treatment, average energy delivered-based PM2.5 EFs were 10 ± 5 mg/kJ (carbonized) and 50 ± 28 mg/kJ (raw) for the biomass and 0.33 ± 0.04 mg/kJ (carbonized) and 3.0 ± 1.3 mg/kJ (raw) for the coal samples. The energy delivered-based EFs of organic carbon, elemental carbon, and 16 priority polycyclic aromatic hydrocarbons extracted from PM2.5 samples from carbonized fuels were reduced by 97 ± 1%, 93 ± 3%, and 97 ± 2%, respectively, for the tested biomass samples, and those for the tested coal samples were 96 ± 1%, 90 ± 6%, and 98 ± 2%, respectively. Average EFs of benzo[a]pyrene equivalent carcinogenic potency for individual polycyclic aromatic hydrocarbons were reduced 95 ± 3% to ~0.51 μg/kJ (carbonized) from ~19.6 μg/kJ (raw). Furthermore, the average ratio of volatile organic compounds contained in PM2.5 samples was also reduced from 38.8 ± 5.4% to 7.1 ± 3.9%. These results suggest that carbonized solid fuels exhibit better performance in reducing carcinogenic potency and pollutants, most of which are highly correlated with the volatile matter content of the fuel. Switching from raw solid fuel to carbonized solid fuel will help to reduce pollutant emissions from household combustion and achieve both environmental benefits and health benefits for household residents.