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1. A uniform <i>p</i>CO₂ climatology combining open and coastal oceans

   https://doi.org/10.5194/essd-12-2537-2020  

   Landschützer, Peter; Laruelle, Goulven G.; Roobaert, Alizee; Regnier, Pierre (January 2020, Earth System Science Data)

   null (Ed.)

   Abstract. In this study, we present the first combined open- and coastal-ocean pCO2 mapped monthly climatology (Landschützer et al., 2020b, https://doi.org/10.25921/qb25-f418, https://www.nodc.noaa.gov/ocads/oceans/MPI-ULB-SOM_FFN_clim.html, last access: 8 April 2020) constructed from observations collected between 1998 and 2015 extracted from the Surface Ocean CO2 Atlas (SOCAT) database. We combine two neural network-based pCO2 products, one from the open ocean and the other from the coastal ocean, and investigate their consistency along their common overlap areas. While the difference between open- and coastal-ocean estimates along the overlap area increases with latitude, it remains close to 0 µatm globally. Stronger discrepancies, however, exist on the regional level resulting in differences that exceed 10 % of the climatological mean pCO2, or an order of magnitude larger than the uncertainty from state-of-the-art measurements. This also illustrates the potential of such an analysis to highlight where we lack a good representation of the aquatic continuum and future research should be dedicated. A regional analysis further shows that the seasonal carbon dynamics at the coast–open interface are well represented in our climatology. While our combined product is only a first step towards a true representation of both the open-ocean and the coastal-ocean air–sea CO2 flux in marine carbon budgets, we show it is a feasible task and the present data product already constitutes a valuable tool to investigate and quantify the dynamics of the air–sea CO2 exchange consistently for oceanic regions regardless of its distance to the coast. 

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2. A multi-decade record of high-quality <i>f</i>CO₂ data in version 3 of the Surface Ocean CO₂ Atlas (SOCAT)

   https://doi.org/10.5194/essd-8-383-2016  

   Bakker, Dorothee C.; Pfeil, Benjamin; Landa, Camilla S.; Metzl, Nicolas; O'Brien, Kevin M.; Olsen, Are; Smith, Karl; Cosca, Cathy; Harasawa, Sumiko; Jones, Stephen D.; et al (January 2016, Earth System Science Data)

   Abstract. The Surface Ocean CO2 Atlas (SOCAT) is a synthesis of quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million fCO2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million fCO2 values relative to version 2 and extends the record from 2011 to 2014. Version 3 also significantly increases the data availability for 2005 to 2013. SOCAT has an average of approximately 1.2 million surface water fCO2 values per year for the years 2006 to 2012. Quality and documentation of the data has improved. A new feature is the data set quality control (QC) flag of E for data from alternative sensors and platforms. The accuracy of surface water fCO2 has been defined for all data set QC flags. Automated range checking has been carried out for all data sets during their upload into SOCAT. The upgrade of the interactive Data Set Viewer (previously known as the Cruise Data Viewer) allows better interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Automated data upload has been launched for version 4 and will enable more frequent SOCAT releases in the future. High-profile scientific applications of SOCAT include quantification of the ocean sink for atmospheric carbon dioxide and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. This ESSD (Earth System Science Data) "living data" publication documents the methods and data sets used for the assembly of this new version of the SOCAT data collection and compares these with those used for earlier versions of the data collection (Pfeil et al., 2013; Sabine et al., 2013; Bakker et al., 2014). Individual data set files, included in the synthesis product, can be downloaded here: doi:10.1594/PANGAEA.849770. The gridded products are available here: doi:10.3334/CDIAC/OTG.SOCAT_V3_GRID. 

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3. Chlorine-initiated oxidation of <i>n</i>-alkanes under high-NO_<i>x</i> conditions: insights into secondary organic aerosol composition and volatility using a FIGAERO–CIMS

   https://doi.org/10.5194/acp-18-15535-2018  

   Wang, Dongyu S.; Hildebrandt Ruiz, Lea (January 2018, Atmospheric Chemistry and Physics)

   Abstract. Chlorine-initiated oxidation of n-alkanes (C₈₋₁₂) under high-nitrogen oxide conditions was investigated. Observed secondary organic aerosol yields (0.16 to 1.65) are higher than those for OH-initiated oxidation of C₈₋₁₂ alkanes (0.04 to 0.35). A high-resolution time-of-flight chemical ionization mass spectrometer coupled to a Filter Inlet for Gases and AEROsols (FIGAERO–CIMS) was used to characterize the gas- and particle-phase molecular composition. Chlorinated organics were observed, which likely originated from chlorine addition to the double bond present on the heterogeneously produced dihydrofurans. A two-dimensional thermogram representation was developed to visualize the composition and relative volatility of organic aerosol components using unit-mass resolution data. Evidence of oligomer formation and thermal decomposition was observed. Aerosol yield and oligomer formation were suppressed under humid conditions (35% to 67% RH) relative to dry conditions (under 5% RH). The temperature at peak desorption signal, T_max, a proxy for aerosol volatility, was shown to change with aerosol filter loading, which should be constrained when evaluating aerosol volatilities using the FIGAERO–CIMS. Results suggest that long-chain anthropogenic alkanes could contribute significantly to ambient aerosol loading over their atmospheric lifetime. 

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4. Terrestrial exospheric dayside H-density profile at 3–15 <i>R</i>_E from UVIS/HDAC and TWINS Lyman-<i>α</i> data combined

   https://doi.org/10.5194/angeo-40-271-2022  

   Zoennchen, Jochen H.; Connor, Hyunju K.; Jung, Jaewoong; Nass, Uwe; Fahr, Hans J. (January 2022, Annales Geophysicae)

   Abstract. Terrestrial ecliptic dayside observations of the exospheric Lyman-α column intensity between 3–15 Earth radii (RE) by UVIS/HDAC (UVIS – ultraviolet imaging spectrograph; HDAC – hydrogen-deuterium absorptioncell) Lyman-α photometer at CASSINI have been analyzed to derive the neutral exospheric H-density profile at the Earth's ecliptic dayside in this radial range. The data were measured during CASSINI's swing-by maneuver at the Earth on 18 August 1999 and are published by Werner et al. (2004). In this study the dayside HDAC Lyman-α observations published by Werner et al. (2004) are compared to calculated Lyman-α intensities based on the 3D H-density model derived from TWINS (Two Wide-angle Imaging Neutral-atom Spectrometers) Lyman-α observations between 2008–2010 (Zoennchen et al., 2015). It was found that both Lyman-α profiles show a very similar radial dependence in particular between 3–8 RE. Between 3.0–5.5 RE impact distance Lyman-α observations of both TWINS and UVIS/HDAC exist at the ecliptic dayside. In this overlapping region the cross-calibration of the HDAC profile against the calculated TWINS profile was done, assuming that the exosphere there was similar for both due to comparable space weather conditions. As a result of the cross-calibration the conversion factor between counts per second and rayleigh, fc=3.285 counts s−1 R−1, is determined for these HDAC observations. Using this factor the radial H-density profile for the Earth's ecliptic dayside was derived from the UVIS/HDAC observations, which constrained the neutral H density there at 10 RE to a value of 35 cm−3. Furthermore, a faster radial H-density decrease was found at distances above 8 RE (≈r-3) compared to the lower distances of 3–7 RE (≈r-2.37). This increased loss of neutral H above 8 RE might indicate a higher rate of H ionization in the vicinity of the magnetopause at 9–11 RE (near subsolar point) and beyond, because of increasing charge exchange interactions of exospheric H atoms with solar wind ions outside the magnetosphere. 

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5. Spatially and temporally resolved measurements of NO_<i>x</i> fluxes by airborne eddy covariance over Greater London

   https://doi.org/10.5194/acp-21-15283-2021  

   Vaughan, Adam R.; Lee, James D.; Metzger, Stefan; Durden, David; Lewis, Alastair C.; Shaw, Marvin D.; Drysdale, Will S.; Purvis, Ruth M.; Davison, Brian; Hewitt, C. Nicholas (January 2021, Atmospheric Chemistry and Physics)

   null (Ed.)

   Abstract. Flux measurements of nitrogen oxides (NOx) were made over London usingairborne eddy covariance from a low-flying aircraft. Seven low-altitude flights were conducted over Greater London, performing multiple overpasses across the city during eight days in July 2014. NOx fluxes across theGreater London region (GLR) exhibited high heterogeneity and strong diurnalvariability, with central areas responsible for the highest emission rates(20–30 mg m−2 h−1). Other high-emission areas included the M25 orbital motorway. The complexity of London's emission characteristics makes it challenging to pinpoint single emissions sources definitively usingairborne measurements. Multiple sources, including road transport andresidential, commercial and industrial combustion sources, are all likely to contribute to measured fluxes. Measured flux estimates were compared toscaled National Atmospheric Emissions Inventory (NAEI) estimates, accountingfor monthly, daily and hourly variability. Significant differences were found between the flux-driven emissions and the NAEI estimates acrossGreater London, with measured values up to 2 times higher in Central London than those predicted by the inventory. To overcome the limitations ofusing the national inventory to contextualise measured fluxes, we usedphysics-guided flux data fusion to train environmental response functions(ERFs) between measured flux and environmental drivers (meteorological and surface). The aim was to generate time-of-day emission surfaces usingcalculated ERF relationships for the entire GLR; 98 % spatial coverage was achieved across the GLR at 400 m2 spatial resolution. All flight legprojections showed substantial heterogeneity across the domain, with highemissions emanating from Central London and major road infrastructure. Thediurnal emission structure of the GLR was also investigated, through ERF,with the morning rush hour distinguished from lower emissions during the early afternoon. Overall, the integration of airborne fluxes with anERF-driven strategy enabled the first independent generation of surfaceNOx emissions, at high resolution using an eddy-covariance approach,for an entire city region. 

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