Assessment of personal exposure to environmentally persistent free radicals in airborne particulate matter

Environmentally persistent free radicals (EPFRs) are a type of emerging contaminants. The EPFR species in airborne particulate matter are similar to carcinogenic tar paramagnetic species in cigarettes that can cause DNA damage. However, understanding on daily EPFR exposure levels and risks are lacking currently. We used personal aerosol exposure monitors worn by volunteers to assess EPFR exposure in a spatio-temporal, non-static manner. Daily individual exposure to EPFRs for urban residents in Beijing, China ranged from 1.11 × 10¹⁷ to 7.42 × 10¹⁷ spins/m³ during the heating period (winter) and from 4.79 × 10¹⁴ to 7.76 × 10¹⁶ spins/m³ during the non-heating period (summer). Carbon-centered radicals were dominant in winter, while oxygen-centered radicals were dominant in summer because of higher atmospheric oxidizing capacity contributing to oxidation reactions. Coal combustion in winter is a key influencing factor in EPFR exposure levels. An intuitional assessment was used to evaluate the inhalation risks of EPFRs by converting their concentrations in inhaled particulate matter to equivalents in cigarettes smoked. The assessment concluded that one urban resident may, on average, inhale the equivalent of 46 cigarettes per day in EPFRs. The health risks of these free radicals, especially during winter, should be researched in depth.