A Scalable Field Study Protocol and Rationale for Passive Ambient Air Sampling: A Spatial Phytosampling for Leaf Data Collection

Abstract

Stable, bioreactive, radicals known as environmentally persistent free radicals (EPFRs) have been found to exist on the surface of airborne PM2.5. These EPFRs have been found to form during many combustion processes, are present in vehicular exhaust, and persist in the environment for weeks and biological systems for up to 12 h. To measure EPFRs in PM samples, high volume samplers are required and measurements are less representative of community exposure; therefore, we developed a novel spatial phytosampling methodology to study the spatial patterns of EPFR concentrations using plants. Leaf samples for laboratory PM analysis were collected from 188 randomly drawn sampling sites within a 500-m buffer zone of pollution sources across a sampling grid measuring 32.9 × 28.4 km in Memphis, Tennessee. PM was isolated from the intact leaves and size fractionated, and EPFRs on PM quantified by electron paramagnetic resonance spectroscopy. The radical concentration was found to positively correlate with the EPFR g-value, thus indicating cumulative content of oxygen centered radicals in PM with higher EPFR load. Our spatial phytosampling approach reveals spatial variations and potential “hotspots” risk due to EPFR exposure across Memphis and provides valuable insights for identifying exposure and demographic differences for health studies.

Environmentally persistent free radicals in PM2.5: a review

“…Chen et al shows that the EPFR concentration was significantly and positively correlated with the concentrations of EC and NO 2 , thus indicating traffic emissions may be the important source of the EPFRs in PM 2.5 [46]. Oyana et al also demonstrated that vehicle emissions may be an important source of EPFRs present in PM 2.5 [41]. Among the 107 leaf samples collected, the top 10 EPFR concentrations (with the highest value of 3.68 × 10 19 spins/g) were all situated in locations where the predominant ambient source was small vehicles, diesel trucks and major industrial sites [41].…”

“…Thus far, we have reported data of EPFRs in airborne PM in six countries, i.e., China, Germany, Greece, India, Saudi Arabia and the USA. As listed in Table 1, there are various forms of sampling media for airborne PM, including a glass fiber filter (GFF) [21,31], quartz fiber filter (QFF) [32][33][34][35], Teflon membrane filter (TMF) [24,36,37], polytetrafluoroethylene (PTFE) [35,38,39], polycarbonate filter (PCF) [40], and even a leaf [41].…”

“…The highest g-value of 2.0048 was observed in PM 3.0 deposited on the leaves in the urban areas of Memphis, USA. The high g-value may well have resulted from the ortho-or para-semiquinone radicals [41]. In terms of line width, it ranged from 3 G [37] to 14.3 G [40].…”

“…It is apparent that the majority (16 out of 23) of the studies show an average g-value between 2.003 and 2.004, which were mostly attributed to semiquinone radicals (Table 4). The three datasets with a g-value greater than 2.004 were all from the research conducted in Memphis [41], while those with the mean g-value less than 2.003 were from Jinan (2.0029) [33] and Xi'an during the fall season (2.0029) [34]; the latter were mostly assigned as carbon-centered radical or carbon-centered radical with adjacent heteroatoms. Overall, an averaged g-value of 2.0035 ± 0.0056 was obtained for all 23 investigations.…”

Size-resolved exposure risk of persistent free radicals (PFRs) in atmospheric aerosols and their potential sources

“…As shown in Figure 2b, the g-factor of summer PM showed a significant decreasing trend with increasing concentration, while the g-factor of winter PM showed a significant increasing trend with increasing EPFR concentration. Oyana et al (2017) studied EPFRs in the surface dust of leaves in the Memphis region of the United States and found that the concentration of EPFRs was positively correlated with the g-factor, and they believed that this was related to the source of EPFRs. This phenomenon indicates that the sources and toxicity of EPFRs in winter and summer are different.…”