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1. Secondary organic aerosol formation from the β-pinene+NO₃ system: effect of humidity and peroxy radical fate

   https://doi.org/10.5194/acp-15-7497-2015  

   Boyd, C. M. ; Sanchez, J. ; Xu, L. ; Eugene, A. J. ; Nah, T. ; Tuet, W. Y. ; Guzman, M. I. ; Ng, N. L. ( January 2015 , Atmospheric Chemistry and Physics)

   Abstract. The formation of secondary organic aerosol (SOA) from the oxidation of β-pinene via nitrate radicals is investigated in the Georgia Tech Environmental Chamber (GTEC) facility. Aerosol yields are determined for experiments performed under both dry (relative humidity (RH) < 2 %) and humid (RH = 50 % and RH = 70 %) conditions. To probe the effects of peroxy radical (RO₂) fate on aerosol formation, "RO₂ + NO₃ dominant" and "RO₂ + HO₂ dominant" experiments are performed. Gas-phase organic nitrate species (with molecular weights of 215, 229, 231, and 245 amu, which likely correspond to molecular formulas of C₁₀H₁₇NO₄, C₁₀H₁₅NO₅, C₁₀H₁₇NO₅, and C₁₀H₁₅NO₆, respectively) are detected by chemical ionization mass spectrometry (CIMS) and their formation mechanisms are proposed. The NO⁺ (at m/z 30) and NO₂⁺ (at m/z 46) ions contribute about 11 % to the combined organics and nitrate signals in the typical aerosol mass spectrum, with the NO⁺ : NO₂⁺ ratio ranging from 4.8 to 10.2 in all experiments conducted. The SOA yields in the "RO₂ + NO₃ dominant" and "RO₂ + HO₂ dominant" experiments are comparable. For a wide range of organic mass loadings (5.1–216.1 μg m^&minus;3), the aerosol mass yield is calculated to be 27.0–104.1 %.more »Although humidity does not appear to affect SOA yields, there is evidence of particle-phase hydrolysis of organic nitrates, which are estimated to compose 45–74 % of the organic aerosol. The extent of organic nitrate hydrolysis is significantly lower than that observed in previous studies on photooxidation of volatile organic compounds in the presence of NO_x. It is estimated that about 90 and 10 % of the organic nitrates formed from the β-pinene+NO₃ reaction are primary organic nitrates and tertiary organic nitrates, respectively. While the primary organic nitrates do not appear to hydrolyze, the tertiary organic nitrates undergo hydrolysis with a lifetime of 3–4.5 h. Results from this laboratory chamber study provide the fundamental data to evaluate the contributions of monoterpene + NO₃ reaction to ambient organic aerosol measured in the southeastern United States, including the Southern Oxidant and Aerosol Study (SOAS) and the Southeastern Center for Air Pollution and Epidemiology (SCAPE) study.

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2. Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene

   https://doi.org/10.5194/acp-18-1643-2018  

   Hinks, Mallory L. ; Montoya-Aguilera, Julia ; Ellison, Lucas ; Lin, Peng ; Laskin, Alexander ; Laskin, Julia ; Shiraiwa, Manabu ; Dabdub, Donald ; Nizkorodov, Sergey A. ( January 2018 , Atmospheric Chemistry and Physics)

   The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NO_x toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at &lt;&thinsp;2 % RH and 75 % RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI&ndash;HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75 % RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from &lt;&thinsp;2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from &lt;&thinsp;2 to 75&ndash;90 % for low-NO_x toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the molecular corridor approach, confirmed that low-NO_x toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NO_x toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions,more »which produce water and oligomers from smaller compounds in low-NO_x toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles.« less
3. Colony formation in <i>Phaeocystis antarctica</i>: connecting molecular mechanisms with iron biogeochemistry

   https://doi.org/10.5194/bg-15-4923-2018  

   Bender, Sara J. ; Moran, Dawn M. ; McIlvin, Matthew R. ; Zheng, Hong ; McCrow, John P. ; Badger, Jonathan ; DiTullio, Giacomo R. ; Allen, Andrew E. ; Saito, Mak A. ( January 2018 , Biogeosciences)

   Abstract. Phaeocystis antarctica is an important phytoplankter of the Ross Sea where it dominates the early season bloom after sea ice retreat and is a major contributor to carbon export. The factors that influence Phaeocystis colony formation and the resultant Ross Sea bloom initiation have been of great scientific interest, yet there is little known about the underlying mechanisms responsible for these phenomena. Here, we present laboratory and field studies on Phaeocystis antarctica grown under multiple iron conditions using a coupled proteomic and transcriptomic approach. P. antarctica had a lower iron limitation threshold than a Ross Sea diatom Chaetoceros sp., and at increased iron nutrition (&gt;120pM Fe') a shift from flagellate cells to a majority of colonial cells in P. antarctica was observed, implying a role for iron as a trigger for colony formation. Proteome analysis revealed an extensive and coordinated shift in proteome structure linked to iron availability and life cycle transitions with 327 and 436 proteins measured as significantly different between low and high iron in strains 1871 and 1374, respectively. The enzymes flavodoxin and plastocyanin that can functionally replace iron metalloenzymes were observed at low iron treatments consistent with cellular iron-sparing strategies, with plastocyanin havingmore »a larger dynamic range. The numerous isoforms of the putative iron-starvation-induced protein (ISIP) group (ISIP2A and ISIP3) had abundance patterns coinciding with that of either low or high iron (and coincident flagellate or the colonial cell types in strain 1871), implying that there may be specific iron acquisition systems for each life cycle type. The proteome analysis also revealed numerous structural proteins associated with each cell type: within flagellate cells actin and tubulin from flagella and haptonema structures as well as a suite of calcium-binding proteins with EF domains were observed. In the colony-dominated samples a variety of structural proteins were observed that are also often found in multicellular organisms including spondins, lectins, fibrillins, and glycoproteins with von Willebrand domains. A large number of proteins of unknown function were identified that became abundant at either high or low iron availability. These results were compared to the first metaproteomic analysis of a Ross Sea Phaeocystis bloom to connect the mechanistic information to the in situ ecology and biogeochemistry. Proteins associated with both flagellate and colonial cells were observed in the bloom sample consistent with the need for both cell types within a growing bloom. Bacterial iron storage and B₁₂ biosynthesis proteins were also observed consistent with chemical synergies within the colony microbiome to cope with the biogeochemical conditions. Together these responses reveal a complex, highly coordinated effort by P. antarctica to regulate its phenotype at the molecular level in response to iron and provide a window into the biology, ecology, and biogeochemistry of this group.

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4. Modeling the physiology of the aquatic temnospondyl <i>Archegosaurusdecheni</i> from the early Permian of Germany

   https://doi.org/10.5194/fr-20-105-2017  

   Witzmann, Florian ; Brainerd, Elizabeth ( January 2017 , Fossil Record)

   Abstract. Physiological aspects like heat balance, gas exchange, osmoregulation, and digestion of the early Permian aquatic temnospondyl Archegosaurus decheni, which lived in a tropical freshwater lake, are assessed based on osteological correlates of physiologically relevant soft-tissue organs and by physiological estimations analogous to air-breathing fishes. Body mass (M) of an adult Archegosaurus with an overall body length of more than 1m is estimated as 7kg using graphic double integration. Standard metabolic rate (SMR) at 20°C (12kJh⁻¹) and active metabolic rate (AMR) at 25°C (47kJh⁻¹) were estimated according to the interspecific allometry of metabolic rate (measured as oxygen consumption) of all fish (V_O2 = 4. 8M^0. 88) and form the basis for most of the subsequent estimations. Archegosaurus is interpreted as a facultative air breather that got O₂ from the internal gills at rest in well-aerated water but relied on its lungs for O₂ uptake in times of activity and hypoxia. The bulk of CO₂ was always eliminated via the gills. Our estimations suggest that if Archegosaurus did not have gills and released 100% CO₂ from its lungs, it would have to breathe much more frequently to release enough CO₂ relative to the lung ventilation required formore »just O₂ uptake. Estimations of absorption and assimilation in the digestive tract of Archegosaurus suggest that an adult had to eat about six middle-sized specimens of the acanthodian fish Acanthodes (ca. 8cm body length) per day to meet its energy demands. Archegosaurus is regarded as an ammonotelic animal that excreted ammonia (NH₃) directly to the water through the gills and the skin, and these diffusional routes dominated nitrogen excretion by the kidneys as urine. Osmotic influx of water through the gills had to be compensated for by production of dilute, hypoosmotic urine by the kidneys. Whereas Archegosaurus has long been regarded as a salamander-like animal, there is evidence that its physiology was more fish- than tetrapod-like in many respects.

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5. Physiological and biochemical responses of <i>Emiliania huxleyi</i> to ocean acidification and warming are modulated by UV radiation

   https://doi.org/10.5194/bg-16-561-2019  

   Tong, Shanying ; Hutchins, David A. ; Gao, Kunshan ( January 2019 , Biogeosciences)

   Abstract. Marine phytoplankton such as bloom-forming, calcite-producingcoccolithophores, are naturally exposed to solar ultraviolet radiation (UVR,280–400nm) in the ocean's upper mixed layers. Nevertheless, the effects ofincreasing carbon dioxide (CO₂)-induced ocean acidification and warming have rarelybeen investigated in the presence of UVR. We examined calcification andphotosynthetic carbon fixation performance in the most cosmopolitancoccolithophorid, Emiliania huxleyi, grown under high(1000µatm, HC; pH_T: 7.70) and low (400µatm,LC; pH_T: 8.02) CO₂ levels, at 15^∘C,20^∘C and 24^∘C with or without UVR. The HCtreatment did not affect photosynthetic carbon fixation at 15^∘C,but significantly enhanced it with increasing temperature. Exposure to UVRinhibited photosynthesis, with higher inhibition by UVA (320–395nm) thanUVB (295–320nm), except in the HC and 24^∘C-grown cells, in whichUVB caused more inhibition than UVA. A reduced thickness of the coccolith layerin the HC-grown cells appeared to be responsible for the UV-inducedinhibition, and an increased repair rate of UVA-derived damage in theHC–high-temperature grown cells could be responsible for lowered UVA-induced inhibition.While calcification was reduced with elevated CO₂ concentration,exposure to UVB or UVA affected the process differentially, with the formerinhibiting it and the latter enhancing it. UVA-induced stimulationmore »of calcification washigher in the HC-grown cells at 15 and 20^∘C, whereas at24^∘C observed enhancement was not significant. The calcificationto photosynthesis ratio (Cal∕Pho ratio) was lower in the HC treatment,and increasing temperature also lowered the value. However, at 20 and24^∘C, exposure to UVR significantly increased the Cal∕Phoratio, especially in HC-grown cells, by up to 100%. This implies thatUVR can counteract the negative effects of the “greenhouse” treatment onthe Cal∕Pho ratio; hence, UVR may be a key stressor when considering theimpacts of future greenhouse conditions on E. huxleyi.

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