Phytosampling-a supplementary tool for particulate matter (PM) speciation characterization

Abstract

Ambient air particulate matter (PM) and PM-associated environmentally persistent free radicals (EPFRs) have been documented to contribute to pollution-related health effects. Studies of ambient air PM potentially bear artifacts stemming from the collection methods. We have investigated the applicability of PM phytosampling (PHS) as a supplementary tool to a classic PM sampler in respect of achieving better PM chemical composition assessment (primarily organic fraction). Phytosampling is a static PM collection method relying on the particle entrapment by the plant's leaf through electrostatic forces and surface trichomes. We have investigated the differences in the EPFR and polycyclic aromatic hydrocarbon (PAH) speciation and concentration on ambient air PM for PHS and high-volume PM sampler (HVS). The advantages of PHS are easy particle recovery from the matrix, collection under natural environmental conditions, and the ability to apply a dense collection network to accurately represent spatial pollutant distribution. The experimental results show that the PHS can provide valuable speciation information, sometimes different from that observed for HVS. For PM collected by PHS, we detected the larger contribution of oxygen-centered EPFRs, different decay behavior, and more consistent PAH distribution between different PM sizes compared to the PM from HVS. These results indicate that the isolation of samples from the ambient during HVS sampling and exposure to high-volume airflow may alter the chemical composition of the samples, while the PHS method could provide details on the original speciation and concentration and be more representative of the PM surface. However, PHS cannot evaluate an absolute air concentration of PM, so it serves as an excellent supplementary tool to work in conjunction with the standard PM collection method.

Keywords: Environmentally persistent free radicals; High-volume PM sampler; PM0.1; PM2.5; Particulate matter; Phytosampling; Polycyclic aromatic hydrocarbons.

Fig. 1

PM entrapment by trichomes on the leaf surface

Fig. 2

Sampling site locations in Google Earth

Fig. 3

PM retrieving procedure

Fig. 4

SEM results on leaf surface before (a1, b1, c1, d1, and e1) and after (a2, b2, c2, d2, and e2) the PM retrieving from two species. a and b are from the leaves of Hedera helix (the common ivy), which were collected from Memphis, TN, for previous study (Oyana et al. 2017). c–e are from the leaves of Ligustrum japonicum (Japanese privet)

Fig. 5

Average g-factor (a), ΔHp-p (b), and spins concentration (c) of EPFRs on PM_0.1, PM_2.5, P₀₂, and P₃. * indicates a statistically significant difference (p<0.01, by ANOVA)

Fig. 6

Comparison of spins concentration of EPFRs on PM_0.1, PM_2.5, P₀₂, and P₃ within the same collection. a is the comparison of EPFR spins concentration between PM_0.1 TAP and PM_2.5 TAP collected from HVS. b is the comparison of EPFR spins concentration between PM_0.1 FD and PM_2.5 FD collected from HVS. And c is the comparison of EPFR spins concentration between P₀₂ and P₃ collected from PHS

Fig. 7

Comparison of average spins concentration (blue line) and average g-factors (red line) of EPFRs on PM from both collection methods under active and passive aging conditions. The blue shade and the red shade represent one standard deviation range of EPFR concentrations and g-factors, respectively. C₀ is the initial EPFR concentration and C is the EPFR concentration after certain decaying time. PM_0.1 and PM_2.5 were collected by HVS, while P₀₂ and P₃ were collected by PHS

Fig. 8

Concentration of total extracted PAHs on PM from HVS (a) and PHS (b)

Fig. 9

Comparisons of PAH concentration percentage on PM from both collection methods within similar particle size. a compares the PAH profiles between P₀₂ and P₃ from two collections by PHS. b compares the PAH profiles between PM_0.1 FD and PM_2.5 FD from three collections by HVS