ALBERT

Description: Mercury is a global toxin that can be introduced to ecosystems through atmospheric deposition. Mercury oxidation is thought to occur in the free troposphere by bromine radicals, but direct observational evidence for this process is currently unavailable. During the 2013 Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks (NOMADSS) campaign, we measured enhanced oxidized mercury and bromine monoxide in a free tropospheric air mass over Texas. We use trace gas measurements, air mass back-trajectories, and a chemical box model to confirm the origin and chemical history of the sampled air mass. We find the presence of elevated oxidized mercury to be consistent with oxidation of elemental mercury by bromine atoms in this subsiding upper tropospheric air mass within the subtropical Pacific High, where dry atmospheric conditions are conducive to oxidized mercury accumulation. Our results support the role of bromine as the dominant oxidant of mercury in the upper troposphere.

Description: Measurements of hydroxyl (OH) and hydroperoxy (HO 2 *) radical concentrations were made at the Pasadena ground site during the CalNex-LA 2010 campaign using the Laser-Induced Fluorescence - Fluorescence Assay by Gas Expansion (LIF-FAGE) technique. The measured concentrations of OH and HO 2 * exhibited a distinct weekend effect, with higher radical concentrations observed on the weekends corresponding to lower levels of nitrogen oxides (NO x ). The radical measurements were compared to results from a zero-dimensional model using the Regional Atmospheric Chemical Mechanism-2 (RACM2) constrained by NO x and other measured trace gases. The chemical model overpredicted measured OH concentrations during the weekends by a factor of approximately 1.4 ± 0.3 (1σ), but the agreement was better during the weekdays (ratio of 1.0 ± 0.2). Model predicted HO 2 * concentrations underpredicted by a factor of 1.3 ± 0.2 on the weekends, while measured weekday concentrations were underpredicted by a factor of 3.0 ± 0.5. However, increasing the modeled OH reactivity to match the measured total OH reactivity improved the overall agreement for both OH and HO 2 * on all days. A radical budget analysis suggests that photolysis of carbonyls and formaldehyde together accounted for approximately 40% of radical initiation with photolysis of nitrous acid accounting for 30% at the measurement height and ozone photolysis contributing less than 20%. An analysis of the ozone production sensitivity reveals that during the week, ozone production was limited by volatile organic compounds throughout the day during the campaign, but NO x -limited during the afternoon on the weekends.

Description: City lights and urban air Nature Geoscience 4, 730 (2011). doi:10.1038/ngeo1300 Authors: H. Stark, S. S. Brown, K. W. Wong, J. Stutz, C. D. Elvidge, I. B. Pollack, T. B. Ryerson, W. P. Dube, N. L. Wagner & D. D. Parrish

Description: Abstract Traditional methods of carbon monitoring in mountainous regions are challenged by complex terrain. Recently, solar‐induced fluorescence (SIF) has been found to be an indicator of gross primary production (GPP), and the increased availability of remotely‐sensed SIF provides an opportunity to estimate GPP across the Western US. Although the empirical linkage between SIF and GPP is strong, the current mechanistic understanding of this linkage is incomplete, and depends upon changes in leaf biochemical processes in which absorbed sunlight leads to photochemistry, heat (via non‐photochemical quenching, NPQ), fluorescence, or tissue damage. An improved mechanistic understanding is necessary to leverage SIF observations to improve representation of ecosystem processes within land surface models. Here, we included an improved fluorescence model within the Community Land Model, Version 4.5 (CLM 4.5) to simulate seasonal changes in SIF at a subalpine forest in Colorado. We found that when the model accounted for sustained NPQ this provided a larger seasonal change in fluorescence yield leading to simulated SIF that more closely resembled the observed seasonal pattern (GOME‐2 satellite platform and a tower‐mounted spectrometer system). We found that an acclimation model based on mean air temperature was a useful predictor for sustained NPQ. Although light intensity was not an important factor for this analysis, it should be considered before applying the sustained NPQ and SIF to other cold climate evergreen biomes. More leaf level fluorescence measurements are necessary to better understand the seasonal relationship between sustained and reversible components of NPQ and to what extent that influences solar‐induced fluorescence.

Description: N-linked glycans play key roles in protein folding, stability, and function. Biosynthetic modification of N-linked glycans, within the endoplasmic reticulum, features sequential trimming and readornment steps. One unusual enzyme, endo-α-mannosidase, cleaves mannoside linkages internally within an N-linked glycan chain, short circuiting the classical N-glycan biosynthetic pathway. Here, using two bacterial orthologs, we present the first structural and mechanistic dissection of endo-α-mannosidase. Structures solved at resolutions 1.7–2.1 Å reveal a (β/α)8 barrel fold in which the catalytic center is present in a long substrate-binding groove, consistent with cleavage within the N-glycan chain. Enzymatic cleavage of authentic Glc1/3Man9GlcNAc2 yields Glc1/3-Man. Using the bespoke substrate α-Glc-1,3-α-Man fluoride, the enzyme was shown to act with retention of anomeric configuration. Complexes with the established endo-α-mannosidase inhibitor α-Glc-1,3-deoxymannonojirimycin and a newly developed inhibitor, α-Glc-1,3-isofagomine, and with the reducing-end product α-1,2-mannobiose structurally define the -2 to +2 subsites of the enzyme. These structural and mechanistic data provide a foundation upon which to develop new enzyme inhibitors targeting the hijacking of N-glycan synthesis in viral disease and cancer.

Description: Because of the importance of HONO as a radical reservoir, consistent and accurate measurements of its concentration are needed. As part of SHARP (Study of Houston Atmospheric Radical Precursors), time series of HONO were obtained by six different measurement techniques on the roof of the Moody Tower (MT) at the University of Houston. Techniques used were long path differential optical absorption spectroscopy (DOAS), stripping coil- visible absorption photometry (SC-AP), long-path absorption photometry (LOPAP®), mist chamber/ ion chromatography (MC-IC), quantum cascade-tunable infrared laser differential absorption spectroscopy (QC-TILDAS) and ion drift -chemical ionization mass spectrometry (ID-CIMS). Various combinations of techniques were in operation from 15 April through 31 May 2009. All instruments recorded a similar diurnal pattern of HONO concentrations with higher median and mean values during the night than during the day. Highest values were observed in the final two weeks of the campaign. Inlets for the MC-IC, SC-AP, and QC-TILDAS were collocated and agreed most closely with each other based on several measures. Largest differences between pairs of measurements were evident during the day for concentrations 〈 ~100 ppt. Above ~ 200 ppt, concentrations from the SC-AP, MC-IC and QC-TILDAS converged to within about 20%, with slightly larger discrepancies when DOAS was considered. During the first two weeks, HONO measured by ID-CIMS agreed with these techniques, but ID-CIMS reported higher values during the afternoon and evening of the final four weeks, possibly from interference from unknown sources. A number of factors, including building related sources, likely affected measured concentrations.

Description: Episodes of elevated bromine oxide (BrO) concentration are known to occur at high latitudes in the Arctic boundary layer and to lead to catalytic destruction of ozone at those latitudes; these events have not been observed at lower latitudes. With the use of differential optical absorption spectroscopy (DOAS), locally high BrO concentrations were observed at mid-latitudes at the Dead Sea, Israel, during spring 1997. Mixing ratios peaked daily at around 80 parts per trillion around noon and were correlated with low boundary-layer ozone mixing ratios.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hebestreit -- Stutz -- Rosen -- Matveiv V -- Peleg -- Luria -- Platt -- New York, N.Y. -- Science. 1999 Jan 1;283(5398):55-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉K. Hebestreit, J. Stutz, U. Platt, Institut fur Umweltphysik, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 366, D-69120 Heidelberg, Germany. D. Rosen, V. Matveiv, M. Peleg, M. Luria, Environmental Science, School of Applie.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9872738" target="_blank"〉PubMed〈/a〉

Description: The United States is now experiencing the most rapid expansion in oil and gas production in four decades, owing in large part to implementation of new extraction technologies such as horizontal drilling combined with hydraulic fracturing. The environmental impacts of this development, from its effect on water quality to the influence of increased methane leakage on climate, have been a matter of intense debate. Air quality impacts are associated with emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs), whose photochemistry leads to production of ozone, a secondary pollutant with negative health effects. Recent observations in oil- and gas-producing basins in the western United States have identified ozone mixing ratios well in excess of present air quality standards, but only during winter. Understanding winter ozone production in these regions is scientifically challenging. It occurs during cold periods of snow cover when meteorological inversions concentrate air pollutants from oil and gas activities, but when solar irradiance and absolute humidity, which are both required to initiate conventional photochemistry essential for ozone production, are at a minimum. Here, using data from a remote location in the oil and gas basin of northeastern Utah and a box model, we provide a quantitative assessment of the photochemistry that leads to these extreme winter ozone pollution events, and identify key factors that control ozone production in this unique environment. We find that ozone production occurs at lower NOx and much larger VOC concentrations than does its summertime urban counterpart, leading to carbonyl (oxygenated VOCs with a C = O moiety) photolysis as a dominant oxidant source. Extreme VOC concentrations optimize the ozone production efficiency of NOx. There is considerable potential for global growth in oil and gas extraction from shale. This analysis could help inform strategies to monitor and mitigate air quality impacts and provide broader insight into the response of winter ozone to primary pollutants.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Edwards, Peter M -- Brown, Steven S -- Roberts, James M -- Ahmadov, Ravan -- Banta, Robert M -- deGouw, Joost A -- Dube, William P -- Field, Robert A -- Flynn, James H -- Gilman, Jessica B -- Graus, Martin -- Helmig, Detlev -- Koss, Abigail -- Langford, Andrew O -- Lefer, Barry L -- Lerner, Brian M -- Li, Rui -- Li, Shao-Meng -- McKeen, Stuart A -- Murphy, Shane M -- Parrish, David D -- Senff, Christoph J -- Soltis, Jeffrey -- Stutz, Jochen -- Sweeney, Colm -- Thompson, Chelsea R -- Trainer, Michael K -- Tsai, Catalina -- Veres, Patrick R -- Washenfelder, Rebecca A -- Warneke, Carsten -- Wild, Robert J -- Young, Cora J -- Yuan, Bin -- Zamora, Robert -- England -- Nature. 2014 Oct 16;514(7522):351-4. doi: 10.1038/nature13767. Epub 2014 Oct 1.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, USA [3] Department of Chemistry, University of York, York YO10 5DD, UK (P.M.E.); Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, 6020 Austria (M.G.); Department of Chemistry, Memorial University of Newfoundland, St John's, Newfoundland A1B 3X7, Canada (C.J.Y.). ; NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA. ; 1] NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, USA. ; Department of Atmospheric Science, University of Wyoming, Larmie, Wyoming 82070, USA. ; Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204, USA. ; Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA. ; Air Quality Research Division, Environment Canada, Toronto, Ontario M3H 5T4, Canada. ; Department of Oceanic and Atmospheric Sciences, University of California, Los Angeles, Los Angeles, California 90095, USA. ; 1] NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] Department of Chemistry, University of York, York YO10 5DD, UK (P.M.E.); Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, 6020 Austria (M.G.); Department of Chemistry, Memorial University of Newfoundland, St John's, Newfoundland A1B 3X7, Canada (C.J.Y.).〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25274311" target="_blank"〉PubMed〈/a〉

Description: Li et al. (Reports, 18 April 2014, p. 292) proposed a unity nitrous acid (HONO) yield for reaction between nitrogen dioxide and the hydroperoxyl-water complex and suggested a substantial overestimation in HONO photolysis contribution to hydroxyl radical budget. Based on airborne observations of all parameters in this chemical system, we have determined an upper-limit HONO yield of 0.03 for the reaction.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ye, Chunxiang -- Zhou, Xianliang -- Pu, Dennis -- Stutz, Jochen -- Festa, James -- Spolaor, Max -- Cantrell, Christopher -- Mauldin, Roy L -- Weinheimer, Andrew -- Haggerty, Julie -- New York, N.Y. -- Science. 2015 Jun 19;348(6241):1326. doi: 10.1126/science.aaa1992.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Wadsworth Center, New York State Department of Health, Albany, NY, USA. ; Wadsworth Center, New York State Department of Health, Albany, NY, USA. Department of Environmental Health Sciences, State University of New York, Albany, NY, USA. xianliang.zhou@health.ny.gov. ; Department of Environmental Health Sciences, State University of New York, Albany, NY, USA. ; University of California, Los Angeles, CA, USA. ; University of Colorado, Boulder, CO, USA. ; University of Colorado, Boulder, CO, USA. Department of Physics, University of Helsinki, Helsinki, Finland. ; National Center for Atmosphere Research, Earth System Laboratory, Boulder, CO, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26089507" target="_blank"〉PubMed〈/a〉

Description: [1]  The California Research at the Nexus of Air Quality and Climate Change (CalNex) field study was conducted throughout California in May, June and July of 2010. The study was organized to address issues simultaneously relevant to atmospheric pollution and climate change, including (1) emission inventory assessment, (2) atmospheric transport and dispersion, (3) atmospheric chemical processing, and (4) cloud-aerosol interactions and aerosol radiative effects. Measurements from networks of ground sites, a research ship, tall towers, balloon-borne ozonesondes, multiple aircraft, and satellites provided in-situ and remotely sensed data on trace pollutant and greenhouse gas concentrations, aerosol chemical composition and microphysical properties, cloud microphysics, and meteorological parameters. This overview report provides operational information for the variety of sites, platforms, and measurements, their joint deployment strategy, and summarizes findings that have resulted from the collaborative analyses of the CalNex field study. Climate-relevant findings from CalNex include leakage from natural gas infrastructure may account for the excess of observed methane over emission estimates in Los Angeles. Air-quality relevant findings include the significant decline in mobile fleet VOC and NOx emissions continues to have an impact on ozone in the Los Angeles basin; the relative contributions of diesel and gasoline emission to secondary organic aerosol are not fully understood; and nighttime NO3 chemistry contributes significantly to secondary organic aerosol mass. Findings simultaneously relevant to climate and air quality include marine vessel emissions changes due to fuel sulfur and speed controls result in a net warming effect, but have substantial positive impacts on local air quality.