On the Relative Contribution of Iron and Organic Compounds, and Their Interaction in Cellular Oxidative Potential of Ambient PM_2.5

Abstract

Previous studies have indicated the roles of both organic compounds and metals in driving the cellular generation of reactive oxygen species (ROS); however, their contribution has not been adequately quantified using mechanistic approaches. We developed a novel fractionation scheme for the stepwise removal of various classes of organic compounds and metals using a combination of solid phase extraction columns. We applied this fractionation scheme to 10 PM 2.5 samples collected from the midwestern United States. Because both watersoluble organic carbon (WSOC) and Fe have shown good correlations with cellular ROS, we separated them into different fractions and measured their ability to generate ROS in rat alveolar macrophages. Most of the PM 2.5 cellular ROS was attributed to the metallic fraction. To further explore the reason for the correlation of WSOC with ROS, we investigated the water solubility of Fe by measuring the total Fe in PM 2.5 samples. The water-soluble fraction of Fe was tightly correlated with WSOC (r ≥ 0.69), indicating WSOC may have an additional role in cellular oxidative potential, probably through complexation of Fe, in enhancing its water solubility and macrophage ROS activity. This work reveals the role of both Fe and organic compounds through different mechanisms in contributing to PM 2.5 -driven cellular ROS.

Oxidized and Unsaturated: Key Organic Aerosol Traits Associated with Cellular Reactive Oxygen Species Production in the Southeastern United States

“…It is noted that cellular ROS production of summer and winter samples is consistently clustered primarily with OOA with less influence by soluble forms of transition metals, suggesting that the ROS production is driven more by OOA than transition metals. Yet, the capability of metals in complexing with organic compounds to generate ROS and enhance aerosol aging should be noted. ,− Also, ROS production may depend on the redox coupling of metals and organics, which could be site-specific. , …”

Assessing the Oxidative Potential of Outdoor PM2.5 in Wintertime Fairbanks, Alaska

“…Consequently, the typical photochemical aging of particles, which can enhance particle toxicity, − is constrained. Other aging processes linked to particle toxicity, such as the solubilization of metals emitted from noncombustion sources, may be restricted by the relatively high particle pH in Fairbanks and low concentrations of organic species, like oxalate, that form soluble metal–organic complexes. − Thus, more characterization of the health-related characteristics of PM 2.5 in populated Arctic regions is needed.…”

Sulfate Formation in Incense Burning Particles: A Single-Particle Mass Spectrometric Study

“…8−12 The plumes commonly contain gaseous reactants (e.g., NO 2 and peroxides), metals (e.g., Fe, Cu), and elemental carbon (EC), which can trigger and catalyze oxidations in the particles. 8,11,13,14 Since incense burning particles are organic rich, 9 the organics could form complexes with Fe to increase its solubility and enhance the oxidants' yield in Fe chemistry, 15 especially under light. 16 Additionally, many of the similar components are photosensitizers (e.g., vanillin) that can generate a variety of oxidants (e.g., triplet molecules, OH radicals, etc.)…”

“…The particle emission factor (i.e., the mass ratio of the emitted particles to the total material burned) from incense burning could be up to 10 times higher than those from burning of various types of biomasses (e.g., rice straw, wood fuel, forest biomass, etc. ), ,, and a high similarity of the chemical compositions of incense and biomass burning plumes has been reported. − The plumes commonly contain gaseous reactants (e.g., NO 2 and peroxides), metals (e.g., Fe, Cu), and elemental carbon (EC), which can trigger and catalyze oxidations in the particles. ,,, Since incense burning particles are organic rich, the organics could form complexes with Fe to increase its solubility and enhance the oxidants’ yield in Fe chemistry, especially under light . Additionally, many of the similar components are photosensitizers (e.g., vanillin) that can generate a variety of oxidants (e.g., triplet molecules, OH radicals, etc.)…”