Abstract: Obtaining Precise Continuous Measurements Of Water Vapor Isotopic Composition In Dry Places (Polar Or High-altitude Regions) Is An Important Challenge. The Current Limitation Is The Strong Influence Of Humidity On The Measured Water Isotopic Composition By Laser Spectroscopy Instruments For Low Humidity Levels (Below 3000 Ppmv). This Problem Is Addressed By Determining The Relationships Between Humidity And Measured δ18o And δD Of Known Water Standards. Here, We Present The Development Of A Robust Field Instrument Able To Generate Water Vapor, Down To 70 Ppmv, At Very Stable Humidity Levels (Average 1σ Lower Than 10 Ppmv). This Instrument, Operated By A Raspberry Interface, Can Be Coupled To A Commercial Laser Spectroscopy Instrument. We Checked The Stability Of The System As Well As Its Accuracy When Expressing The Measured Isotopic Composition Of Water Vapor On The Vsmow–slap (Vienna Standard Mean Ocean Water – Standard Light Antarctic Precipitation) Scale. It Proved To Be Highly Stable During Autonomous Operation Over More Than 1 Year At The East Antarctic Concordia And Dumont D'urville Stations.

Abstract: This Paper Assesses The Quality Of Iasi (Infrared Atmospheric Sounding Interferometer)/metop-a (Iasi-a) And Iasi/metop-b (Iasi-b) Ozone (O3) Products (Total And Partial O3 Columns) Retrieved With The Fast Optimal Retrievals On Layers For Iasi Ozone (Forli-o3; V20151001) Software For 9 Years (2008–july 2017) Through An Extensive Intercomparison And Validation Exercise Using Independent Observations (Satellite, Ground-based And Ozonesonde). Compared With The Previous Version Of Forli-o3 (V20140922), Several Improvements Have Been Introduced In Forli-o3 V20151001, Including Absorbance Look-up Tables Recalculated To Cover A Larger Spectral Range, With Additional Numerical Corrections. This Leads To A Change Of ∼4% In The Total Ozone Column (Toc) Product, Which Is Mainly Associated With A Decrease In The Retrieved O3 Concentration In The Middle Stratosphere (Above 30hpa/25km). Iasi-a And Iasi-b Tocs Are Consistent, With A Global Mean Difference Of Less Than 0.3% For Both Daytime And Nighttime Measurements; Iasi-a Is Slightly Higher Than Iasi-b. A Global Difference Of Less Than 2.4% Is Found For The Tropospheric (Tropo) O3 Column Product (Iasi-a Is Lower Than Iasi-b), Which Is Partly Due To A Temporary Issue Related To The Iasi-a Viewing Angle In 2015. Our Validation Shows That Iasi-a And Iasi-b Tocs Are Consistent With Gome-2 (Global Ozone Monitoring Experiment-2), Dobson, Brewer, Saoz (Système D'analyse Par Observation Zénithale) And Ftir (Fourier Transform Infrared) Tocs, With Global Mean Differences In The Range Of 0.1%–2% Depending On The Instruments Compared. The Worst Agreement With Uv–vis Retrieved Toc (Satellite And Ground) Is Found At The Southern High Latitudes. The Iasi-a And Ground-based Toc Comparison For The Period From 2008 To July 2017 Shows The Long-term Stability Of Iasi-a, With Insignificant Or Small Negative Drifts Of 1%–3%decade−1. The Comparison Results Of Iasi-a And Iasi-b Against Smoothed Ftir And Ozonesonde Partial O3 Columns Vary With Altitude And Latitude, With The Maximum Standard Deviation Being Seen For The 300–150hpa Column (20%–40%) Due To Strong Ozone Variability And Large Total Retrievals Errors. Compared With Ozonesonde Data, The Iasi-a And Iasi-b O3 Tropo Column (Defined As The Column Between The Surface And 300hpa) Is Positively Biased In The High Latitudes (4%–5%) And Negatively Biased In The Midlatitudes And Tropics (11%–13% And 16%–19%, Respectively). The Iasi-a-to-ozonesonde Tropo Comparison For The Period From 2008 To 2016 Shows A Significant Negative Drift In The Northern Hemisphere Of -8.6±3.4%decade−1, Which Is Also Found In The Iasi-a-to-ftir Tropo Comparison. When Considering The Period From 2011 To 2016, The Drift Value For The Tropo Column Decreases And Becomes Statistically Insignificant. The Observed Negative Drifts Of The Iasi-a Tropo O3 Product (8%–16%decade−1) Over The 2008–2017 Period Might Be Taken Into Consideration When Deriving Trends From This Product And This Time Period.

Abstract: The nitrogen stable isotopic composition in nitrate (δ15N-NO−3) measured in ice cores from low-snow-accumulation regions in East Antarctica has the potential to provide constraints on past ultraviolet (UV) radiation and thereby total column ozone (TCO) due to the sensitivity of nitrate (NO−3) photolysis to UV radiation. However, understanding the transfer of reactive nitrogen at the air–snow interface in polar regions is paramount for the interpretation of ice core records of δ15N-NO−3 and NO−3 mass concentrations. As NO−3 undergoes a number of post-depositional processes before it is archived in ice cores, site-specific observations of δ15N-NO−3 and air–snow transfer modelling are necessary to understand and quantify the complex photochemical processes at play. As part of the Isotopic Constraints on Past Ozone Layer Thickness in Polar Ice (ISOL-ICE) project, we report new measurements of NO−3 mass concentration and δ15N-NO−3 in the atmosphere, skin layer (operationally defined as the top 5 mm of the snowpack), and snow pit depth profiles at Kohnen Station, Dronning Maud Land (DML), Antarctica. We compare the results to previous studies and new data, presented here, from Dome C on the East Antarctic Plateau. Additionally, we apply the conceptual 1D model of TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) to assess the impact of NO−3 recycling on δ15N-NO−3 and NO−3 mass concentrations archived in snow and firn. We find clear evidence of NO−3 photolysis at DML and confirmation of previous theoretical, field, and laboratory studies that UV photolysis is driving NO−3 recycling and redistribution at DML. Firstly, strong denitrification of the snowpack is observed through the δ15N-NO−3 signature, which evolves from the enriched snowpack (−3 ‰ to 100 ‰), to the skin layer (−20 ‰ to 3 ‰), to the depleted atmosphere (−50 ‰ to −20 ‰), corresponding to mass loss of NO−3 from the snowpack. Based on the TRANSITS model, we find that NO−3 is recycled two times, on average, before it is archived in the snowpack below 15 cm and within 0.75 years (i.e. below the photic zone). Mean annual archived δ15N-NO−3 and NO−3 mass concentration values are 50 ‰ and 60 ng g−1, respectively, at the DML site. We report an e-folding depth (light attenuation) of 2–5 cm for the DML site, which is considerably lower than Dome C. A reduced photolytic loss of NO−3 at DML results in less enrichment of δ15N-NO−3 than at Dome C mainly due to the shallower e-folding depth but also due to the higher snow accumulation rate based on TRANSITS-modelled sensitivities. Even at a relatively low snow accumulation rate of 6 cm yr−1 (water equivalent; w.e.), the snow accumulation rate at DML is great enough to preserve the seasonal cycle of NO−3 mass concentration and δ15N-NO−3, in contrast to Dome C where the depth profiles are smoothed due to longer exposure of surface snow layers to incoming UV radiation before burial. TRANSITS sensitivity analysis of δ15N-NO−3 at DML highlights that the dominant factors controlling the archived δ15N-NO−3 signature are the e-folding depth and snow accumulation rate, with a smaller role from changes in the snowfall timing and TCO. Mean TRANSITS model sensitivities of archived δ15N-NO−3 at the DML site are 100 ‰ for an e-folding depth change of 8 cm, 110 ‰ for an annual snow accumulation rate change of 8.5 cm yr−1 w.e., 10 ‰ for a change in the dominant snow deposition season between winter and summer, and 10 ‰ for a TCO change of 100 DU (Dobson units). Here we set the framework for the interpretation of a 1000-year ice core record of δ15N-NO−3 from DML. Ice core δ15N-NO−3 records at DML will be less sensitive to changes in UV than at Dome C; however the higher snow accumulation rate and more accurate dating at DML allows for higher-resolution δ15N-NO−3 records.

Abstract: Multiple year-round (2006–2015) records of the bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located in East Antarctica. The well-marked maximum of non-sea-salt sulfate (nssSO₄) in January (100 ± 28 ng m⁻³ versus 4.4 ± 2.3 ng m⁻³ in July) is consistent with observations made at the coast (280 ± 78 ng m⁻³ in January versus 16 ± 9 ng m⁻³ in July at Dumont d'Urville, for instance). In contrast, the well-marked maximum of MSA at the coast in January (60 ± 23 ng m⁻³ at Dumont d'Urville) is not observed at Concordia (5.2 ± 2.0 ng m⁻³ in January). Instead, the MSA level at Concordia peaks in October (5.6 ± 1.9 ng m⁻³) and March (14.9 ± 5.7 ng m⁻³). As a result, a surprisingly low MSA-to-nssSO₄ ratio (R_MSA) is observed at Concordia in mid-summer (0.05 ± 0.02 in January versus 0.25 ± 0.09 in March). We find that the low value of R_MSA in mid-summer at Concordia is mainly driven by a drop of MSA levels that takes place in submicron aerosol (0.3 µm diameter). The drop of MSA coincides with periods of high photochemical activity as indicated by high ozone levels, strongly suggesting the occurrence of an efficient chemical destruction of MSA over the Antarctic plateau in mid-summer. The relationship between MSA and nssSO₄ levels is examined separately for each season and indicates that concentration of non-biogenic sulfate over the Antarctic plateau does not exceed 1 ng m⁻³ in fall and winter and remains close to 5 ng m⁻³ in spring. This weak non-biogenic sulfate level is discussed in the light of radionuclides (²¹⁰Pb, ¹⁰Be, and ⁷Be) also measured on bulk aerosol samples collected at Concordia. The findings highlight the complexity in using MSA in deep ice cores extracted from inland Antarctica as a proxy of past dimethyl sulfide emissions from the Southern Ocean.

Abstract: Abstract. Variations In The Stable Oxygen Isotope Composition Of Atmospheric Nitrate Act As Novel Tools For Studying Oxidative Processes Taking Place In The Troposphere. They Provide Both Qualitative And Quantitative Constraints On The Pathways Determining The Fate Of Atmospheric Nitrogen Oxides (No + No2 = Nox). The Unique And Distinctive 17o Excess (Δ17o = δ17o − 0.52 × δ18o) Of Ozone, Which Is Transferred To Nox Via Oxidation, Is A Particularly Useful Isotopic Fingerprint In Studies Of Nox Transformations. Constraining The Propagation Of 17o Excess Within The Nox Cycle Is Critical In Polar Areas, Where There Exists The Possibility Of Extending Atmospheric Investigations To The Glacial–interglacial Timescale Using Deep Ice Core Records Of Nitrate. Here We Present Measurements Of The Comprehensive Isotopic Composition Of Atmospheric Nitrate Collected At Dome C (East Antarctic Plateau) During The Austral Summer Of 2011/2012. Nitrate Isotope Analysis Has Been Here Combined For The First Time With Key Precursors Involved In Nitrate Production (Nox, O3, Oh, Ho2, Ro2, Etc.) And Direct Observations Of The Transferrable Δ17o Of Surface Ozone, Which Was Measured At Dome C Throughout 2012 Using Our Recently Developed Analytical Approach. Assuming That Nitrate Is Mainly Produced In Antarctica In Summer Through The Oh + No2 Pathway And Using Concurrent Measurements Of Oh And No2, We Calculated A Δ17o Signature For Nitrate On The Order Of (21–22 ± 3) ‰. These Values Are Lower Than The Measured Values That Ranged Between 27 And 31 ‰. This Discrepancy Between Expected And Observed Δ17o(no3−) Values Suggests The Existence Of An Unknown Process That Contributes Significantly To The Atmospheric Nitrate Budget Over This East Antarctic Region. However, Systematic Errors Or False Isotopic Balance Transfer Functions Are Not Totally Excluded.