title: Contribution of water-soluble and insoluble components and their hydrophobic/hydrophilic subfractions to the reactive oxygen species-generating potential of fine ambient aerosols.
abstract: Relative contributions of water- and methanol-soluble compounds and their hydrophobic/hydrophilic subfractions to the ROS (reactive oxygen species)-generating potential of ambient fine aerosols (D(p) < 2.5 μm) are assessed. ROS-generating (or oxidative) potential of the particulate matter (PM) was measured by the dithiothreitol (DTT) assay. Particles were collected on quartz filters (N = 8) at an urban site near central Atlanta during January-February 2012 using a PM(2.5) high-volume sampler. Filter punches were extracted separately in both water and methanol. Hydrophobic and hydrophilic fractions were then subsequently segregated via a C-18 solid phase extraction column. The DTT assay response was significantly higher for the methanol extract, and for both extracts a substantial fraction of PM oxidative potential was associated with the hydrophobic compounds as evident from a substantial attenuation in DTT response after passing PM extracts through the C-18 column (64% for water and 83% for methanol extract; both median values). The DTT activities of water and methanol extracts were correlated with the water-soluble (R = 0.86) and water-insoluble organic carbon (R = 0.94) contents of the PM, respectively. Brown carbon (BrC), which predominantly represents the hydrophobic organic fraction (referred to as humic-like substances, HULIS), was also correlated with DTT activity in both the water (R = 0.78) and methanol extracts (R = 0.83). Oxidative potential was not correlated with any metals measured in the extracts. These findings suggest that the hydrophobic components of both water-soluble and insoluble organic aerosols substantially contribute to the oxidative properties of ambient PM. Further investigation of these hydrophobic organic compounds could help identify sources of a significant fraction of ambient aerosol toxicity.
authors.affiliation: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: Vishal
authors.initials: V
authors.lastname: Verma
authors.forename: Roberto
authors.initials: R
authors.lastname: Rico-Martinez
authors.forename: Neel
authors.initials: N
authors.lastname: Kotra
authors.forename: Laura
authors.initials: L
authors.lastname: King
authors.forename: Jiumeng
authors.initials: J
authors.lastname: Liu
authors.forename: Terry W
authors.initials: TW
authors.lastname: Snell
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Weber
mesh_terms: D000336:Aerosols / Q000032:analysis* / Q000737:chemistry; D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008956:Models, Chemical; D052638:Particulate Matter / Q000032:analysis* / Q000737:chemistry; D017382:Reactive Oxygen Species / Q000032:analysis* / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D052638:Particulate Matter; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical