Study on Non-Metal-Induced EPFRs in PM_2.5 Generated from Flue Gas of Cellulose Combustion

Environmental persistent free radicals (EPFRs) are a type of environmental risk substances existing in atmospheric particulate matter, which pose a challenge to human survival and sustainable development. The current understanding is that the formation mechanism of EPFRs is generally related to metallic materials. However, this study analyzed the PM_2.5 generated from cellulose combustion and found that EPFRs could be generated even without the metallic materials. Therefore, this paper explores the emission characteristics of non-metal-induced EPFRs, aiming to reveal the influencing factors, distribution, and decay characteristics of non-metal-induced EPFRs generated from cellulose combustion. The results show that combustion conditions such as combustion temperature and oxygen concentration have a significant impact on the emission concentration of non-metal-induced EPFRs in PM_2.5 from cellulose combustion. The emission concentrations of non-metal-induced EPFRs in PM_2.5 are at the order of magnitude of 10¹⁴ spins/m³ and over 50% is distributed in the inextricable substances. Their g-factor are in the range from 2.0015 to 2.0022, indicating that these EPFRs are carbon-centered radicals. Furthermore, non-metal-induced EPFRs in PM_2.5 from cellulose combustion have a half-life of several years or even longer, which exhibit distinct characteristics different from metal-induced EPFRs.