Identification and Quantification of Dust-Located Environmentally Persistent Free Radicals

Airborne fine particulate matter (PM2.5) has been extensively identified as a major contributor to adverse health outcomes, including respiratory illnesses, cardiovascular diseases, and premature mortality. PM2.5 poses an even greater threat due to the presence of environmentally persistent free radicals (EPFRs). It is, thus, important to study human exposure to EPFRs. Dust samples from residential areas in Al Ain, UAE, were tested, and free radicals were detected and quantified. ESR measurements showed distinct signals with g-factors around 2.004–2.006, typically associated with oxygen-centered EPFRs. Spin concentrations were quantified at approximately 2.64 × 1016 spins/g in Dust Sample 1 (DS1) and 2.36 × 1017 spins/g in Dust Sample 2 (DS2), values comparable to those reported in other regions. DS1 and DS2 were collected from two different locations in inhabited areas of the city of Al Ain. Fourier Transform InfraRed (FTIR) spectra revealed possible functional groups such as catechols and hydroquinones, while X-ray diffraction (XRD) confirmed mineral oxides that could stabilize these radicals. However, the spectra also displayed features consistent with the six-line hyperfine splitting of Mn. These findings confirm the presence of environmentally relevant paramagnetic species in dust, which have implications for human health.