Fine particle pH and the partitioning of nitric acid during winter in the northeastern United States

Particle pH is a critical but poorly constrained quantity that affects many aerosol processes and properties, including aerosol composition, concentrations, and toxicity. We assess PM1 pH as a function of geographical location and altitude, focusing on the northeastern U.S., based on aircraft measurements from the Wintertime Investigation of Transport, Emissions, and Reactivity campaign (1 February to 15 March 2015). Particle pH and water were predicted with the ISORROPIA-II thermodynamic model and validated by comparing predicted to observed partitioning of inorganic nitrate between the gas and particle phases. Good agreement was found for relative humidity (RH) above 40%; at lower RH observed particle nitrate was higher than predicted, possibly due to organic-inorganic phase separations or nitrate measurement uncertainties associated with low concentrations (nitrate \u3c 1 µg m−3). Including refractory ions in the pH calculations did not improve model predictions, suggesting they were externally mixed with PM1 sulfate, nitrate, and ammonium. Sample line volatilization artifacts were found to be minimal. Overall, particle pH for altitudes up to 5000 m ranged between −0.51 and 1.9 (10th and 90th percentiles) with a study mean of 0.77 ± 0.96, similar to those reported for the southeastern U.S. and eastern Mediterranean. This expansive aircraft data set is used to investigate causes in variability in pH and pH-dependent aerosol components, such as PM1 nitrate, over a wide range of temperatures (−21 to 19°C), RH (20 to 95%), inorganic gas, and particle concentrations and also provides further evidence that particles with low pH are ubiquitous

Results from the DC-8 Inlet Characterization Experiment (DICE): Airborne Versus Surface Sampling of Mineral Dust and Sea Salt Aerosols

During May and June of 2003 NASA conducted the DC-8 Inlet Characterization Experiment (DICE). The study was undertaken to quantify the performance of three passive, solid diffuser inlets used aboard the DC-8 aircraft to sample optically effective aerosol sizes. Aerosol optical properties measured behind the University of Hawai’i (UH) and the University of New Hampshire (UNH) inlets were within 10% of the ground based measurements whereas the NASALangley (LaRC) inlet reduced scattering values for supermicrometer dust by approximately 50%. Based on the DICE results the aerodynamic 50% passing efficiency of the inlets and transport plumbing is determined to be above 5.0 and 4.1 μmfor the UH and UNHinlets and 3.6μmfor theLaRCinlet. These aerodynamic sizes correspond to geometric particle diameters of 3.1, 2.5, and 2.0 μm ignoring shape factor and assuming particle densities of 2.6 g cm−3. Sea salt aerosols sampled at high relative humidity revealed that the UH and the UNH inlets performed nearly identically in the marine environment. Aerosol optical properties measured behind the UH inlet were within 30% of measurements made at the NOAA/ESRL Trinidad Head Observatory and in some cases were better than 10%.We conclude that quantitative measurements of optical properties and processes linked to aerosol surface chemistry can be effectively studied aboard theNASA DC-8 using the UH and UNH inlets because aerosol particles less than 4 μm in aerodynamic diameter typically dominate aerosol optical properties and surface area

Deciphering Redox State for a Metal-Rich World

Abstract The Psyche mission’s Oxidation-Reduction Working Group is focused on understanding, determining, and applying the redox state of (16) Psyche to understand the origin of a metal-rich world. The oxidation-reduction state of an asteroid, along with its temperature, parent body size, and composition, is a key parameter in determining the history of an asteroid. Determining the redox state from spacecraft data is most easily done by examining potential metal-oxide buffer pairs. The occurrence of Ni, Fe, C, Cr, P and Si, in that order, in the metal or sulfide phase of an asteroidal body indicates increasingly reduced conditions. Key observations by the Imager and Gamma-Ray and Neutron Spectrometer (GRNS) of Psyche can bracket the redox state using metal-oxide buffers. The presence of Fe,Ni metal can be confirmed by the ratios of Fe/O or Fe/Si and the concentration of Ni variability in metal across the asteroid can be determined by GRNS. The FeO concentration of silicates is complementary to the Ni concentration of metal and can be constrained using filters on the Imager. The presence of FeO in silicates from ground-based observations is one of the few measurements we already have of redox state, although available data permit a wide range of silicate compositions and mineralogies. The presence of C, P or Si concentrated in the metallic, Fe-rich portion of the asteroid, as measured by GRNS, or Ca-sulfide, determined by imaging, would indicate increasingly reducing conditions. Linkage to known types of meteorites, whether metal-rich chondrites, stony-irons or irons, expands the mineralogical, chemical and isotopic data not available from remote observations alone. Redox also controls both silicate and metal mineralogy, influencing differentiation, solidification, and subsolidus cooling, including the relative abundance of sulfur in the core and possible magnetic signatures. The redox state of Psyche, if a fully-differentiated metallic core, might constrain the location and timing of both the formation of Psyche and any oxidation it might have experienced

Wintertime gas-particle partitioning and speciation of inorganic chlorine in the lower troposphere over the Northeast United States and coastal ocean

The formation of photolabile chlorine reservoirs depend on how much chloride is available in the particle to react, which requires the chlorine partitioning to the particle in the troposphere to be well understood. However, limited measurements of gas and particle composition necessary to constrain this chemistry exist. We present measurements from the Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign that show inorganic tropospheric chlorine compounds (Cly) measured in the lower troposphere are dominated by HCl and PM4 particulate chloride (pCl−), with contributions from trace chlorine species like nitryl chloride (ClNO2), hypochlorous acid (HOCl), and molecular chlorine (Cl2). We observed elevated Cly mixing ratios over the ocean (540–625 pptv) compared to over land (178–225 pptv). Observations show 0–20% (0–0.2 μg/m3) of measured chlorine partitions into particles with a diameter less than 1 μm under typical WINTER conditions. The thermodynamic model, ISORROPIA II, overpredicts submicron pCl− by a factor of 2 but is brought into agreement, assuming a small fraction of unmeasured, refractory sea salt \u3c0.1 μg/m3 exists. The model-measurement disagreement could also be caused by an effective equilibrium constant for HCl that is too large. We derive a lower-limit equilibrium function (Keq = 2.5 × 106 exp[5,208(1/T − 1/T0)] mol2·kg−2·atm−1) that lowers the model value\u27s temperature dependency. This work provides constraints on Cly in the troposphere, addresses the sensitivity of chlorine partitioning to minor changes in environmental variables, and highlights the remaining questions interfering with our ability to correctly model pCl− concentrations

Antarctic Tropospheric Chemistry Investigation (ANTCI) 2003 overview

The Antarctic Tropospheric Chemistry Investigation (ANTCI) was carried out from late November to December 2003 with both extended ground-based and tethered balloon studies at Amundsen Scott Station, South Pole. ANTCI 2003 was the first of two Antarctic field studies with the primary goal of further exploring the active photochemistry of the South Pole region that was first identified in the previous Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program. Since ISCAT was fully ground-based, ANTCI 2003 goals included expanding chemical studies both vertically upward to investigate mixing and horizontally to better understand large-scale plateau NO, production and transport. Thus, in addition to ground-based experiments at South Pole, Twin Otter aircraft sampling took place out to hundreds of kilometers in several directions from the South Pole. These were designed to specifically address the issue of how representative past South Pole chemical measurements are of the surrounding high plateau region. The Twin Otterwas also used to make transects along the coast both north and south of McMurdo Station. The present paper summarizes the overall setting and results of this investigation and highlights the many new findings that were obtained

Distinguishing the Origin of Asteroid (16) Psyche

Abstract The asteroid (16) Psyche may be the metal-rich remnant of a differentiated planetesimal, or it may be a highly reduced, metal-rich asteroidal material that never differentiated. The NASA Psyche mission aims to determine Psyche’s provenance. Here we describe the possible solar system regions of origin for Psyche, prior to its likely implantation into the asteroid belt, the physical and chemical processes that can enrich metal in an asteroid, and possible meteoritic analogs. The spacecraft payload is designed to be able to discriminate among possible formation theories. The project will determine Psyche’s origin and formation by measuring any strong remanent magnetic fields, which would imply it was the core of a differentiated body; the scale of metal to silicate mixing will be determined by both the neutron spectrometers and the filtered images; the degree of disruption between metal and rock may be determined by the correlation of gravity with composition; some mineralogy (e.g., modeled silicate/metal ratio, and inferred existence of low-calcium pyroxene or olivine, for example) will be detected using filtered images; and the nickel content of Psyche’s metal phase will be measured using the GRNS

Distinguishing the Origin of Asteroid (16) Psyche

International audienceThe asteroid (16) Psyche may be the metal-rich remnant of a differentiated planetesimal, or it may be a highly reduced, metal-rich asteroidal material that never differentiated. The NASA Psyche mission aims to determine Psyche's provenance. Here we describe the possible solar system regions of origin for Psyche, prior to its likely implantation into the asteroid belt, the physical and chemical processes that can enrich metal in an asteroid, and possible meteoritic analogs. The spacecraft payload is designed to be able to discriminate among possible formation theories. The project will determine Psyche's origin and formation by measuring any strong remanent magnetic fields, which would imply it was the core of a differentiated body; the scale of metal to silicate mixing will be determined by both the neutron spectrometers and the filtered images; the degree of disruption between metal and rock may be determined by the correlation of gravity with composition; some mineralogy (e.g., modeled silicate/metal ratio, and inferred existence of low-calcium pyroxene or olivine, for example) will be detected using filtered images; and the nickel content of Psyche's metal phase will be measured using the GRNS

High levels of nitryl chloride in the polluted subtropical marine boundary layer

The cycling of halogen compounds in the lower atmosphere is poorly understood. It is known that halogens such as chlorine, bromine and iodine are converted from halides, which are relatively inert, to reactive radicals. These reactive radicals can affect ozone production and destruction, aerosol formation and the lifetimes of important trace gases such as methane, mercury and naturally occurring sulphur compounds. However, the processes by which halides are converted to reactive halogens are uncertain. Here, we report atmospheric measurements of nitryl chloride, an active halogen, along the southeast coastline of the United States and near Houston, Texas. We show that the main source of nitryl chloride is the night-time reaction of dinitrogen pentoxide with chloride-containing aerosol. The levels observed are much greater than earlier estimates based on numerical models and are sufficiently large to affect oxidant photochemistry in areas where nitrogen oxides and aerosol chloride sources coexist, such as urban areas and ship engine exhaust plumes