Characterization of Atmospheric Iron Speciation and Acid Processing at Metropolitan Newark on the US East Coast

Abstract

Abstract:To characterize atmospheric dissolved iron over Newark, a large metropolitan city on US east coast, size-segregated (0.056-18 µm in aerodynamic diameter) aerosols were collected in downtown Newark, New Jersey during August to October 2012. Aerosols samples were analyzed for Fe(II) and total dissolved iron (Fe(TD)) by UV/Visible spectroscopy, and water soluble compounds were analyzed by ion chromatograph (IC). Results from this study showed that Fe(II) concentrations were 2.1 ng m −3 (range: 1.2-4.2 ng m −3 ), Fe(TD) concentrations were 2.4 ng m −3 (range: 1.3-4.9 ng m −3 ). Dissolved iron (Fe(II) and Fe(TD)) in general appeared as bi-modal size distribution, was mainly accumulated in the fine mode. The highest concentration of dissolved iron displayed in the fine mode, which was associated with high concentrations of sulfate, oxalate and nitrate, suggesting the potential for Fe-acids interactions. Dissolved iron presented positive correlations with sulfate in the coarse mode, and with nitrate in the fine mode, further suggesting the importance of acid processing in aerosol iron solubility. However, as the oxalate concentration was so low, a good correlation between dissolved iron and oxalate in both the fine and coarse mode was not found.

Understanding the Impact of Relative Humidity and Coexisting Soluble Iron on the OH-Initiated Heterogeneous Oxidation of Organophosphate Flame Retardants

“…These monodispersed particles were then passed through the headspace of a temperature-controlled Pyrex tube (333–343 K) containing either pure liquid TCP or TBEP to generate coated particles with a calculated coating thickness of approximately 15 nm (calculated based upon the shift in the peak of the particle size distribution). The estimated iron concentration inside the flow tube reactor (∼0.7 μg m –3 ) is comparable to the total mass concentration of iron in ambient aerosols , but is higher than the water-soluble iron concentration in ambient aerosols. , The coated particles were introduced into a mixing vessel after having passed through an activated carbon denuder to remove volatile organics vapors from the flow. Upon the basis of an evaporation model described previously, the evaporation of the OPFRs studied here was estimated to contribute less than 0.3% to the particle-phase loss of OPFRs within the residence time of the mixing vessel and flow tube reactor (see SI).…”

“…The estimated iron concentration inside the flow tube reactor (∼0.7 μg m −3 ) is comparable to the total mass concentration of iron in ambient aerosols 33,34 but is higher than the watersoluble iron concentration in ambient aerosols. 35,36 The coated particles were introduced into a mixing vessel after having passed through an activated carbon denuder to remove volatile organics vapors from the flow. Upon the basis of an evaporation model described previously, 42 the evaporation of the OPFRs studied here was estimated to contribute less than 0.3% to the particle-phase loss of OPFRs within the residence time of the mixing vessel and flow tube reactor (see SI).…”

“…In the atmosphere, the fate of OPFRs present in the gas-phase is determined by OH-initiated oxidation reactions, with well-known measured and modeled chemical kinetics. − However, many atmospheric OPFRs such as TCP, TBEP, TPhP, TDCPP, TCEP, and TCPP are predominantly associated with airborne particles, − where their fate is not only dependent on the OH-initiated heterogeneous degradation kinetics but also other components of the complex matrix in particles with which particle-bound OPFRs are associated. During their residence time in the atmosphere, the particle-bound OPFR degradation is likely affected by factors such as ambient relative humidity (RH), particle physical properties (e.g., phase state), and particle chemical composition, all of which have been demonstrated to be important in the transformation and transport of atmospheric organic aerosols (OA) in general. − For example, organic aerosols may exist in different phase states, ranging from solid to semisolid and liquid particles in response to changes in ambient RH, , thus affecting the heterogeneous reaction rates of aerosol components with trace gaseous species. , In addition, the coexistence of metallic and organic species in ambient aerosols is also known to occur. − The presence of metallic species such as iron, one of the most abundant transition metals observed in atmospheric aerosols (up to 5.22 μg m –3 ), − may increase the overall oxidation rates of particle-bound organics via Fenton-type reactions that produce reactive oxygen species (ROS) such as particle-phase OH. , …”

13C Probing of Ambient Photo-Fenton Reactions Involving Iron and Oxalic Acid: Implications for Oceanic Biogeochemistry

“…This means that absolute atmospheric abundances of oxalic acid and nss-SO 4 2– are not directly responsible for the observed higher Fe ws (%) in the SEA outflow, underscoring the role of another parameter/process. On the basis of the prevailing large difference in the mass concentrations of SO 4 2– and oxalic acid in ambient aerosols, it has been often argued that acid processing might alone control the atmospheric abundances of Fe ws . ,,, However, recent studies have emphasized the role of atmospheric acidity (i.e., represented here by the aerosol pH estimated using the E-AIM II model) in forming SOA (e.g., oxalic acid). ,,− Accordingly, we found significant linear relationships of aerosol pH with the molar mass concentrations of oxalic acid and Fe ws in both the continental outflows (IGP and SEA; Figure ). Better correlations were observed here for the SEA outflow samples, suggesting that aerosol acidity over the remote oceans controls both the formation of SOA (e.g., oxalic acid) and Fe ws .…”

“…On the basis of the prevailing large difference in the mass concentrations of SO 4 2− and oxalic acid in ambient aerosols, it has been often argued that acid processing might alone control the atmospheric abundances of Fe ws . 28,50,95,96 However, recent studies have emphasized the role of atmospheric acidity (i.e., represented here by the aerosol pH estimated using the E-AIM II model) in forming SOA (e.g., oxalic acid). 51,71,97−102 Accordingly, we found significant linear relationships of aerosol pH with the molar mass concentrations of oxalic acid and Fe ws in both the continental outflows (IGP and SEA; Figure 3).…”