Real-World Emission Characteristics of Environmentally Persistent Free Radicals in PM2.5 from Residential Solid Fuel Combustion

Environmentally persistent free radicals (EPFRs) can induce reactive oxygen species, causing adverse health impacts, and residential fuel (biomass and coal) combustion is believed to be an important emission source for EPFRs; however, the residential emission characteristics of EPFRs are rarely studied in the real world. Here, we conducted a field campaign evaluating the presence and characteristics of EPFRs generated from residential biomass and coal burning in rural China. The emission factors (EFs) of EPFRs (with units of 10(20) spins.kg(-1)) in PM2.5 from the combustion of crop residues (3.97 +/- 0.47) were significantly higher than those from firewood (2.06 +/- 0.19) and coal (2.13 +/- 0.33) (p < 0.05). The EPFRs from residential solid fuel combustion were carbon-centered free radicals adjacent to oxygen atoms. The fuel type was a primary factor controlling EPFR discharge, explaining 68% of the variation in EPFR EFs. The emissions from biomass burning had higher EPFRs per particle than those from coal combustion. EPFRs had stronger relationships with carbonaceous components than with other incomplete combustion products. The EPFRs from biomass burning were mostly generated during the pyrolysis of fuels, while the EPFRs generated from coal combustion were mainly associated with refractory organic compounds. This study provides valuable information for evaluating the fates of EPFRs, promoting a better understanding of the health impacts of air pollution.

Automated summary

Residential biomass and coal burning are important emission sources for environmentally persistent free radicals (EPFRs). This study conducted a field campaign in rural China to evaluate the presence and characteristics of EPFRs generated from residential biomass and coal burning. The results showed that EPFRs emissions from crop residues burning were significantly higher than those from firewood and coal. Fuel type was found to be the primary factor controlling EPFR discharge. Biomass burning had higher EPFRs per particle compared to coal combustion. EPFRs had stronger relationships with carbonaceous components. EPFRs from biomass burning were mainly generated during the pyrolysis of fuels, while EPFRs from coal combustion were mainly associated with refractory organic compounds.