Is the oxidative potential of components of fine particulate matter surface-mediated?

Redox-active substances in fine particulate matter (PM) contribute to inhalation health risks through their potential to generate reactive oxygen species in epithelial lung lining fluid (ELF). The ELF's air-liquid interface (ALI) can play an important role in the phase transfer and multi-phase reactions of redox-active PM constituents. We investigated the influence of interfacial processes and properties by scrubbing of coated nano-particles with simulated ELF in a nebulizing mist chamber. Weakly water-soluble redox-active organics abundant in ambient fine PM were reproducibly loaded into ELF via ALI mixing. The resulting oxidative potential (OP) of selected quinones and other PAH derivatives were found to exceed the OP resulting from bulk mixing of the same amounts of redox-active substances and ELF. Our results indicate that the OP of PM components depends not only on the PM substance properties but also on the ELF interface properties and uptake mechanisms. OP measurements based on bulk mixing of phases may not represent the effective OP in the human lung.

Oxygenated and Nitrated Polycyclic Aromatic Hydrocarbons in Ambient Air-Levels, Phase Partitioning, Mass Size Distributions, and Inhalation Bioaccessibility.

Among the nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are some of the most hazardous substances to public health, mainly because of their carcinogenicity and oxidative potential. Despite these concerns, the concentrations and fate of NPAHs and OPAHs in the atmospheric environment are largely unknown. Ambient air concentrations of 18 NPAHs, 5 quinones, and 5 other OPAHs were determined at two urban and one regional background sites in central Europe. At one of the urban sites, the total (gas and particulate) concentrations of Σ10OPAHs were 10.0 ± 9.2 ng/m3 in winter and 3.5 ± 1.6 ng/m3 in summer. The gradient to the regional background site exceeded 1 order of magnitude. Σ18NPAH concentrations were typically 1 order of magnitude lower than OPAHs. Among OPAHs, 9-fluorenone and (9,10)-anthraquinone were the most abundant species, accompanied by benzanthrone in winter. (9,10)-Anthraquinone represented two-thirds of quinones. We found that a large fraction of the target substance particulate mass was carried by submicrometer particles. The derived inhalation bioaccessibility in the PM10 size fraction is found to be ≈5% of the total ambient concentration of OPAHs and up to ≈2% for NPAHs. For 9-fluorenone and (9,10)-anthraquinone, up to 86 and 18%, respectively, were found at the rural site. Our results indicate that water solubility could function as a limiting factor for bioaccessibility of inhaled particulate NPAHs and OPAHs, without considerable effect of surfactant lipids and proteins in the lung lining fluid.

Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules.

Highly oxygenated molecules (HOMs) play an important role in the formation and evolution of secondary organic aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of laboratory-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By electron paramagnetic resonance and mass spectrometric investigations, we found that the relative abundance of HOMs, especially the dimeric and low-volatility types, in ambient fine PM was positively correlated with the formation of radicals in aqueous PM extracts. SOA from photooxidation of isoprene, ozonolysis of α- and ß-pinene, and fine PM from tropical (central Amazon) and boreal (Hyytiälä, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidation of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chemical relationship of HOM abundance, composition, and sources with the yield of radicals by laboratory and ambient aerosols, enabling better quantification of the component-specific contribution of source- or site-specific fine PM to its climate and health effects.

Antioxidant activity of cerium dioxide nanoparticles and nanorods in scavenging hydroxyl radicals.

Cerium oxide nanoparticles (CeNPs) have been shown to exhibit antioxidant capabilities, but their efficiency in scavenging reactive oxygen species (ROS) and the underlying mechanisms are not yet well understood. In this study, cerium dioxide nanoparticles (CeNPs) and nanorods (CeNRs) were found to exhibit much stronger scavenging activity than ·OH generation in phosphate buffered saline (PBS) and surrogate lung fluid (SLF). The larger surface area and higher defect density of CeNRs may lead to higher ·OH scavenging activity than for CeNPs. These insights are important to understand the redox activity of cerium nanomaterials and provide clues to the role of CeNPs in biological and environmental processes.