An extensive set of volatile organic compounds (VOCs) and particulate organic matter (POM) was measured in polluted air during the New England Air Quality Study in 2002. Using VOC ratios, the ...photochemical age of the sampled air masses was estimated. This approach was validated (1) by comparing the observed rates at which VOCs were removed from the atmosphere with the rates expected from OH oxidation, (2) by comparing the VOC emission ratios inferred from the data with the average composition of urban air, and (3) by the ability to describe the increase of an alkyl nitrate with time in terms of the chemical kinetics. A large part of the variability observed for oxygenated VOCs (OVOCs) and POM could be explained by a description that includes the removal of the primary anthropogenic emissions, the formation and removal of secondary anthropogenic species, and a biogenic contribution parameterized by the emissions of isoprene. The OVOC sources determined from the data are compared with the available literature, and a satisfactory agreement is obtained. The observed sub‐μm POM was highly correlated with secondary anthropogenic gas‐phase species, strongly suggesting that the POM was from secondary anthropogenic sources. The results are used to describe the speciation and total mass of gas‐ and particle‐phase organic carbon as a function of the photochemical age of an urban air mass. Shortly after emission the organic carbon mass is dominated by primary VOCs, while after two days the dominant contribution is from OVOCs and sub‐μm POM. The total measured organic carbon mass decreased by about 40% over the course of two days. The increase in sub‐μm POM could not be explained by the removal of aromatic precursors alone, suggesting that other species must have contributed and/or that the mechanism for POM formation is more efficient than previously assumed.
Current global inventories of ammonia emissions identify the ocean as the largest natural source. This source depends on seawater pH, temperature, and the concentration of total seawater ammonia ...(NHx(sw)), which reflects a balance between remineralization of organic matter, uptake by plankton, and nitrification. Here we compare NHx(sw) from two global ocean biogeochemical models (BEC and COBALT) against extensive ocean observations. Simulated NHx(sw) are generally biased high. Improved simulation can be achieved in COBALT by increasing the plankton affinity for NHx within observed ranges. The resulting global ocean emissions is 2.5 TgN a−1, much lower than current literature values (7–23 TgN a−1), including the widely used Global Emissions InitiAtive (GEIA) inventory (8 TgN a−1). Such a weak ocean source implies that continental sources contribute more than half of atmospheric NHx over most of the ocean in the Northern Hemisphere. Ammonia emitted from oceanic sources is insufficient to neutralize sulfate aerosol acidity, consistent with observations. There is evidence over the Equatorial Pacific for a missing source of atmospheric ammonia that could be due to photolysis of marine organic nitrogen at the ocean surface or in the atmosphere. Accommodating this possible missing source yields a global ocean emission of ammonia in the range 2–5 TgN a−1, comparable in magnitude to other natural sources from open fires and soils.
Key Points
New observational constraints on the ocean atmosphere ammonia flux
Ocean NH3 flux to the atmosphere is lower than previous estimates
Photolysis of organic N may contribute to the release of N from the ocean
Reliable characterization of particles freshly emitted from the ocean surface requires a sampling method that is able to isolate those particles and prevent them from interacting with ambient gases ...and particles. Here we report measurements of particles directly emitted from the ocean using a newly developed in situ particle generator (Sea Sweep). The Sea Sweep was deployed alongside R/V Atlantis off the coast of California during May of 2010. Bubbles were generated 0.75 m below the ocean surface with stainless steel frits and swept into a hood/vacuum hose to feed a suite of aerosol instrumentation on board the ship. The number size distribution of the directly emitted, nascent particles had a dominant mode at 55–60 nm (dry diameter) and secondary modes at 30–40 nm and 200–300 nm. The nascent aerosol was not volatile at 230°C and was not enriched in SO4=, Ca++, K+, or Mg++above that found in surface seawater. The organic component of the nascent aerosol (7% of the dry submicrometer mass) volatilized at a temperature between 230 and 600°C. The submicrometer organic aerosol characterized by mass spectrometry was dominated by non‐oxygenated hydrocarbons. The nascent aerosol at 50, 100, and 145 nm dry diameter behaved hygroscopically like an internal mixture of sea salt with a small organic component. The CCN/CN activation ratio for 60 nm Sea Sweep particles was near 1 for all supersaturations of 0.3 and higher indicating that all of the particles took up water and grew to cloud drop size. The nascent organic aerosol mass fraction did not increase in regions of higher surface seawater chlorophyll but did show a positive correlation with seawater dimethylsulfide (DMS).
Key Points
The ocean is a source of sub 100nm particles to the atmosphere
Hygroscopically the particles behave like an internal mixture of sea salt/organic
Organic mass fraction did not correlate with chlorophyll
Organic compounds were measured by proton transfer reaction‐mass spectrometry (PTR‐MS) on board the National Oceanic and Atmospheric Administration's research ship Ronald H. Brown during the New ...England Air Quality Study (NEAQS) in July and August of 2002. PTR‐MS has the potential to measure many important organic species with a fast time response, but its validity has not been proven sufficiently. The results obtained by PTR‐MS during NEAQS were compared with those from (oxygenated) hydrocarbon measurements by gas chromatography/mass spectrometry (GC‐MS), peroxyacyl nitrate measurements by gas chromatography/electron capture detection, and carboxylic acid measurements by mist chamber/ion chromatography. The PTR‐MS and GC‐MS data for methanol, acetonitrile, acetone, isoprene, benzene, and toluene agreed within the measurement uncertainties. The comparison for C8 aromatics and acetaldehyde was less quantitative due to calibration inaccuracies. In addition, PTR‐MS measured the sum of methyl vinyl ketone and methacrolein at 71 amu, the sum of C9 aromatics at 121 amu, and the sum of monoterpenes at 81 and 137 amu. The PTR‐MS signal at 61 amu was found to correlate well with data for acetic acid. The signal at 73 amu correlated reasonably well with methyl ethyl ketone data, but the quantitative disagreement suggested interference from other species, possibly methyl glyoxal. The signal at 77 amu correlated well with data for peroxyacetyl nitrate, and the sensitivity inferred from the field data agreed within 30% with the results from laboratory calibrations. Finally, the signal at 105 amu was attributed to styrene and peroxy isobutyryl nitrate. These results prove that many important organic species can be measured accurately and with a fast response time by PTR‐MS.
Observations and model calculations indicate that highly non-linear multiphase atmospheric processes involving inorganic Cl and Br significantly impact tropospheric chemistry and composition, aerosol ...evolution, and radiative transfer. The sensitivity of global atmospheric chemistry to the production of marine aerosol and the associated activation and cycling of inorganic Cl and Br was investigated using a size-resolved multiphase coupled chemistry–global climate model (National Center for Atmospheric Research's Community Atmosphere Model (CAM) v3.6.33). Simulated results revealed strong meridional and vertical gradients in Cl and Br species. They also point to possible physicochemical mechanisms that may account for several previously unexplained phenomena, including the enrichment of Br- in submicron aerosol and the presence of a BrO maximum in the polar free troposphere. However, simulated total volatile inorganic Br mixing ratios in the troposphere were generally higher than observed, due in part to the overly efficient net production of BrCl. In addition, the emission scheme for marine aerosol and associated Br−, which is the only source for Br in the model, overestimates emission fluxes from the high-latitude Southern Ocean. Br in the stratosphere was lower than observed due to the lack of long-lived precursor organobromine species in the simulation. Comparing simulations using chemical mechanisms with and without reactive Cl and Br species demonstrates a significant temporal and spatial sensitivity of primary atmospheric oxidants (O3, HOx, NOx), CH4, non-methane hydrocarbons (NMHCs), and dimethyl sulfide (DMS) to halogen cycling. Globally, halogen chemistry had relatively less impact on SO2 and non-sea-salt (nss) SO42− although significant regional differences were evident. Although variable geographically, much of this sensitivity is attributable to either over-vigorous activation of Br (primarily BrCl) via the chemical mechanism or overproduction of sea-salt aerosol simulated under higher-wind regimes. In regions where simulated mixing ratios of reactive Br and Cl fell within observed ranges, though, halogen chemistry drove large changes in oxidant fields and associated chemical processes relative to simulations with no halogens. However, the overall simulated impacts of Br chemistry globally are overestimated and thus caution is warranted in their interpretation.
A parameterization for the size- and composition-resolved production fluxes of nascent marine aerosol was developed from prior experimental observations and extrapolated to ambient conditions based ...on estimates of air entrainment by the breaking of wind-driven ocean waves. Production of particulate organic carbon (OCaer) was parameterized based on Langmuir equilibrium-type association of organic matter to bubble plumes in seawater and resulting aerosol as constrained by measurements of aerosol produced from productive and oligotrophic seawater. This novel approach is the first to parameterize size- and composition-resolved aerosol production based on explicit evaluation of wind-driven air entrainment/detrainment fluxes and chlorophyll-a as a proxy for surfactants in surface seawater. Production fluxes were simulated globally with an eight aerosol-size-bin version of the NCAR Community Atmosphere Model (CAM v3.5.07). Simulated production fluxes fell within the range of published estimates based on observationally constrained parameterizations. Because the parameterization does not consider contributions from spume drops, the simulated global mass flux (1.5 × 103 Tg y−1) is near the lower end of published estimates. The simulated production of aerosol number (1.4 × 106 m−2 s−1) and OCaer (29 Tg C y−1) fall near the upper end of published estimates and suggest that primary marine aerosols may have greater influences on the physicochemical evolution of the troposphere, radiative transfer and climate, and associated feedbacks on the surface ocean than suggested by previous model studies.
Physical and biogeochemical processes in seawater controlling primary marine aerosol (PMA) production and composition are poorly understood and associated with large uncertainties in estimated fluxes ...into the atmosphere. PMA production was investigated in the biologically productive NE Pacific Ocean and in biologically productive and oligotrophic regions of the NW Atlantic Ocean. Physicochemical properties of model PMA, produced by aeration of fresh seawater under controlled conditions, were quantified. Diel variability in model PMA mass and number fluxes was observed in biologically productive waters, increasing following sunrise and decreasing to predawn levels overnight. Such variability was not seen in oligotrophic waters. During daytime, surfactant scavenging by aeration in the aerosol generator without replenishing the seawater in the reservoir reduced the model PMA production in productive waters to nighttime levels but had no influence on production from oligotrophic waters. Results suggest bubble plume interactions with sunlight‐mediated biogenic surfactants in productive seawater significantly enhanced model PMA production.
Key Points
Surface ocean biogeochemistry mediates physics of marine aerosol production
Diel cycles in biologically productive surface seawater mediate production
Observations show chemical processes affecting mass and number production fluxes
Striatal and cortical mitochondria from knock‐in and transgenic mutant huntingtin mice were examined for their sensitivity to calcium induction of the permeability transition, a cause of ...mitochondrial depolarization and ATP loss. The permeability transition has been suggested to contribute to cell death in Huntington's Disease. Mitochondria were examined from slowly progressing knock‐in mouse models with different length polyglutarnine expansions (Q20, Q50, Q92, Q111) and from the rapidly progressing transgenic R6/2 mice overexpressing exon I of human huntingtin with more than 110 polyglutamines. As previously observed in rats, striatal mitochondria from background strain CD1 and C57BL/6 control mice were more sensitive to calcium than cortical mitochondria. Between 5 and 12 months in knock‐in Q92 mice and between 8 and 12 weeks in knock‐in Q111 mice, striatal mitochondria developed resistance, becoming equally sensitive to calcium as cortical mitochondria, while those from Q50 mice were unchanged. Cortical mitochondrial calcium sensitivity did not change. In R6/2 mice striatal and cortical mitochondria were equally resistant to Ca2+ while striatal mitochondria from littermate controls were more susceptible. No increases in calcium sensitivity were observed in the mitochondria from Huntington's Disease (HD) mice compared to controls. Neither motor abnormalities, nor expression of cyclophilin D corresponded to the changes in mitochondrial sensitivity. Polyglutamine expansions in huntingtin produced an early increased resistance to calcium in striatal mitochondria suggesting mitochondria undergo compensatory changes in calcium sensitivity in response to the many cellular changes wrought by polyglutamine expansion.
This study examines atmospheric reactive chlorine chemistry at the Cape Verde Atmospheric Observatory in the eastern tropical Atlantic. During May–June, 2007, Cl2 levels ranged from below detection ...(∼2 ppt) to 30 ppt. Elevated Cl2 was associated with high HNO3 (40 to 120 ppt) in polluted continental outflow transported in the marine boundary layer (MBL) to the site. Lower Cl2 was observed in recently subsided air masses with multiday free tropospheric oceanic trajectories and in air containing Saharan dust. Model simulations show that the observations of elevated Cl2 in polluted marine air are consistent with initiation of Cl chemistry by OH + HCl and subsequent heterogeneous, autocatalytic Cl cycling involving marine aerosols. Model estimates suggest that Cl atom reactions significantly impact the fates of methane and dimethylsulfide at Cape Verde and are moderately important for ozone cycling.
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