Environmentally Persistent Free Radicals and Their Lifetimes in PM_2.5

Abstract

For the first time, an expansive study into the concentration and extended decay behavior of environmentally persistent free radicals in PM2.5 was performed. Results from this study revealed three types of radical decay—a fast decay, slow decay, and no decay—following one of four decay patterns: a relatively fast decay exhibiting a 1/e lifetime of 1–21 days accompanied by a slow decay with a 1/e lifetime of 21–5028 days (47% of samples); a single slow decay including a 1/e lifetime of 4–2083 days (24% of samples); no decay (18% of samples); and a relatively fast decay displaying an average 1/e lifetime of 0.25–21 days followed by no decay (11% of samples). Phenol correlated well with the initial radical concentration and fast decay rate. Other correlations for common atmospheric pollutants (ozone, NOx, SO2, etc.) as well as meteorological conditions suggested photochemical processes impact the initial radical concentration and fast decay rate. The radical signal in PM2.5 was remarkably similar to semiquinones in cigarette smoke. Accordingly, radicals inhaled from PM2.5 were related to the radicals inhaled from smoking cigarettes, expressed as the number of equivalent cigarettes smoked. This calculated to 0.4–0.9 cigarettes per day for nonextreme air quality in the United States.

Formation of environmentally persistent free radical (EPFR) in iron(iii) cation-exchanged smectite clay

“…This mechanism is consistent with the EPFR formation mechanism proposed for PM 2.5. 36-37 The XANES data presented in Fig. 5 reveal additional mechanistic information beyond the oxidation state of Fe redox centres in the formation of EPFRs.…”

Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

“…In addition, PM 2.5 contains environmentally persistent free radicals (EPFR) that can be detected directly by electron paramagnetic resonance (EPR) spectroscopy Gehling and Dellinger, 2013). EPFR are stable radicals with an e folding lifetime exceeding one day (Gehling and Dellinger, 2013;Jia et al, 2016).…”

“…EPFR are stable radicals with an e folding lifetime exceeding one day (Gehling and Dellinger, 2013;Jia et al, 2016). The chemical nature of EPFR is remarkably similar to semiquinone radicals, which can be stabilized via electron transfer with transition metals in the particle phase (Truong et al, 2010;Vejerano et al, 2011;Gehling and Dellinger, 2013). EPFR are formed upon combustion and pyrolysis of organic matter (Dellinger et al, , 2007.…”

Air Phytoremediation

“…Formation of EPFR occurs when oxidized metals as CuO 2 , ZnO 2 , and FeO 2 are reduced by the delivery of electron from organic compounds [10]. The new structures become free radicals, lasting from days for phenoxy radicals to months and even years for semiquinone radicals [11]. It is worth noting that present in significant quantities in the air, nontoxic form of iron oxide after the entry into reactions with organic gaseous pollutants becomes very reactive pollutant as well as forming EPFR.…”