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Global chemistry-climate models (CCMs) play an important role in assessing the climate and air pollution implications of aerosols and chemically reactive gases. Evaluating these models under past conditions and constraining historical sources and sinks necessitates reliable records of atmospheric mixing ratios spanning preindustrial times. Such precious records were recently obtained for carbon monoxide (CO) documenting for the first time the evolution of this reactive compound over the industrial era. In this study, we compare the simulated atmospheric surface CO mixing ratios ([CO]) from two different sets of CCMs and emissions in the frame of CMIP5 and of CMIP6 (Coupled Model Intercomparison Project Phases 5 and 6) with recent bipolar ice archive reconstructions for the period spanning 1850 to present. We analyze how historical (1850–2014) [CO] outputs from 16 (Atmospheric Chemistry and Climate Model Intercomparison Project) models and 6 AerChemMIP (Aerosol Chemistry Model Intercomparison Project) models over Greenland and Antarctica are able to capture both absolute values and trends recorded in multi-site ice archives. While most models underestimate [CO] at high northern latitudes, a reduction in this bias is observed from ACCMIP to AerChemMIP exercises. Over the 1980–2010 CE period, trends in ice archive and firn air observations and AerChemMIP outputs align remarkably well at high northern and southern latitudes, indicating improved quantification of CO anthropogenic emissions and the main CO sink (OH oxidation) compared to ACCMIP. From 1850 to 1980 CE, AerChemMIP models and observations consistently show increasing [CO] in both the Northern Hemisphere (NH) and Southern Hemisphere (SH), suggesting a robust understanding of the CO budget evolution. However, a divergence in the [CO] growth rate emerges in NH between models and observations over the 1920–1975 CE period, attributed to uncertainties in CO emission factors (EF), particularly EF for RCO (Residential, Commercial and Others) and transportation sectors, although we cannot totally rule out that the CO record based on Greenland ice archives may be biased high by CO chemical production processes occurring in the ice prior the measurements (i.e., in situ CO production). In the Southern Hemisphere, AerChemMIP models simulate an increase in atmospheric [CO] from 1850 to 1980 CE closely reproducing the observations (22±10 ppb and 13±7 ppb, respectively). Such agreement supports CMIP6 biomass burning CO emission inventories which do not reveal a peak in CO emissions in the late 19th century. Furthermore, both SH models and observations reveal an accelerated growth rate in [CO] during 1945–1980 CE relative to 1980–1945 CE, likely linked to increased anthropogenic transportation emissions. [ABSTRACT FROM AUTHOR]

Year‐round precipitation in coastal East Antarctica and Antarctic Peninsula was used to investigate the seasonal patterns in sources of atmospheric perchlorate (ClO4− ${{\text{ClO}}_{4}}^{-}$). Although featuring distinct climates, the two locations exhibit similar annual mean and seasonal cycles of ClO4− ${{\text{ClO}}_{4}}^{-}$ concentration, with higher values in autumn and lower concentrations in winter and spring. Tropospheric formation dominates atmospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ in spring and summer, which is influenced by both oxidants levels and environmental conditions (e.g., air humidity). Tropospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ production may also be promoted by elevated levels of oxidants brought by air mass from the interior Antarctic ice sheet in spring and summer. The autumn concentration maximum may originate from ClO4− ${{\text{ClO}}_{4}}^{-}$ produced in the stratosphere through reactions between reactive chlorine and ozone during spring and summer. In winter, the stratospheric input may contribute to ClO4− ${{\text{ClO}}_{4}}^{-}$ via polar stratospheric clouds sedimentation. Plain Language Summary: Perchlorate (ClO4− ${{\text{ClO}}_{4}}^{-}$) is an inorganic anion with a persistent presence in the environment, where its exposure can pose a significant health risk to humans. Environmental ClO4− ${{\text{ClO}}_{4}}^{-}$ is derived from both man‐made and natural sources. Natural ClO4− ${{\text{ClO}}_{4}}^{-}$, widespread in the environment, is thought to be formed in the atmosphere. However, knowledge on the sources and, in particular, the formation mechanisms of natural ClO4− ${{\text{ClO}}_{4}}^{-}$ is quite limited. Antarctica, with negligible man‐made sources, is one of the best regions for investigations on natural ClO4− ${{\text{ClO}}_{4}}^{-}$. Year‐round precipitation samples were collected at China Zhongshan Station located in coastal East Antarctica and China Great Wall Station on King George Island, Antarctic Peninsula. Results show that atmospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ concentration presents obvious seasonal cycles, which are related to variations in sources. A significant amount of ClO4− ${{\text{ClO}}_{4}}^{-}$ is associated with tropospheric chemistry in spring and summer. Precursor levels, environmental conditions, and air mass from the interior Antarctica may influence tropospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ formation. The maximum concentration in autumn may originate from ClO4− ${{\text{ClO}}_{4}}^{-}$ formed in the stratosphere during spring and summer, and the stratospheric input may also contribute to atmospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ in winter. Key Points: Antarctic atmospheric perchlorate (ClO4− ${{\text{ClO}}_{4}}^{-}$) concentration at different locations exhibits a clear seasonal cycleThe highest concentration in autumn is likely related to ClO4− ${{\text{ClO}}_{4}}^{-}$ produced in the stratosphere in spring and summerMajor source of ClO4− ${{\text{ClO}}_{4}}^{-}$ in spring and summer is tropospheric formation influenced by both oxidants and environmental conditions [ABSTRACT FROM AUTHOR]

The NASA Atmospheric Tomography Mission (ATom) completed four seasonal deployments (August 2016, February 2017, October 2017, May 2018), each with regular 0.2–12 km profiling by transecting the remote Pacific Ocean and Atlantic Ocean basins. Additional data were also acquired for the Southern Ocean, the Arctic basin, and two flights over Antarctica. ATom in situ measurements provide a near-complete chemical characterization of the ∼ 140 000 10 s (80 m by 2 km) air parcels measured along the flight path. This paper presents the Modeling Data Stream (MDS), a continuous gap-filled record of the 10 s parcels containing the chemical species needed to initialize a gas-phase chemistry model for the budgets of tropospheric ozone and methane. Global 3D models have been used to calculate the Reactivity Data Stream (RDS), which is comprised of the chemical reactivities (production and loss) for methane, ozone, and carbon monoxide, through 24 h integration of the 10 s parcels. These parcels accurately sample tropospheric heterogeneity and allow us to partially deconstruct the spatial scales and variability that define tropospheric chemistry from composition to reactions. This paper provides a first look at and analysis of the up-to-date MDS and RDS data including all four deployments (Prather et al., 2023, 10.7280/D1B12H). ATom's regular profiling of the ocean basins allows for weighted averages to build probability densities for the key species and reactivities presented here. These statistics provide climatological metrics for global chemistry models, e.g., the large-scale pattern of ozone and methane loss in the lower troposphere and the more sporadic hotspots of ozone production in the upper troposphere. The profiling curtains of reactivity also identify meteorologically variable and hence deployment-specific hotspots of photochemical activity. Added calculations of the sensitivities of the production and loss terms relative to each species emphasize the few dominant species that control the ozone and methane budgets and whose statistical patterns should be key model–measurement metrics. From the sensitivities, we also derive linearized lifetimes of ozone and methane on a parcel-by-parcel basis and average over the basins, providing an observational basis for these previously model-only diagnostics. We had found that most model differences in the ozone and methane budgets are caused by the models calculating different climatologies for the key species such as O 3 , CO, H 2 O, NO x , CH 4 , and T , and thus these ATom measurements make a substantial contribution to the understanding of model differences and even identifying model errors in global tropospheric chemistry. [ABSTRACT FROM AUTHOR]

Nitrogen oxides, collectively referred to as NO x (NO + NO 2), are an important component of atmospheric chemistry involved in the production and destruction of various oxidants that contribute to the oxidative capacity of the troposphere. The primary sink for NO x is atmospheric nitrate, which has an influence on climate and the biogeochemical cycling of reactive nitrogen. NO x sources and NO x -to-NO 3- formation pathways remain poorly constrained in the remote marine boundary layer of the Southern Ocean, particularly outside of the more frequently sampled summer months. This study presents seasonally resolved measurements of the isotopic composition (δ15 N, δ18 O, and Δ17 O) of atmospheric nitrate in coarse-mode (> 1 µ m) aerosols, collected between South Africa and the sea ice edge in summer, winter, and spring. Similar latitudinal trends in δ15 N–NO 3- were observed in summer and spring, suggesting similar NO x sources. Based on δ15 N–NO 3- , the main NO x sources were likely a combination of lightning, biomass burning, and/or soil emissions at the low latitudes, as well as oceanic alkyl nitrates and snowpack emissions from continental Antarctica or the sea ice at the mid-latitudes and high latitudes, respectively. Snowpack emissions associated with photolysis were derived from both the Antarctic snowpack and snow on sea ice. A combination of natural NO x sources, likely transported from the lower-latitude Atlantic, contribute to the background-level NO 3- observed in winter, with the potential for a stratospheric NO 3- source evidenced by one sample of Antarctic origin. Greater values of δ18 O–NO 3- in spring and winter compared to summer suggest an increased influence of oxidation pathways that incorporate oxygen atoms from O 3 into the end product NO 3- (i.e. N 2 O 5 , DMS, and halogen oxides (XO)). Significant linear relationships between δ18 O and Δ17 O suggest isotopic mixing between H 2 O (v) and O 3 in winter and isotopic mixing between H 2 O (v) and O 3 /XO in spring. The onset of sunlight in spring, coupled with large sea ice extent, can activate chlorine chemistry with the potential to increase peroxy radical concentrations, contributing to oxidant chemistry in the marine boundary layer. As a result, isotopic mixing with an additional third end-member (atmospheric O 2) occurs in spring. [ABSTRACT FROM AUTHOR]

The NASA Atmospheric Tomography (ATom) Mission completed four seasonal deployments (August 2016, February 2017, October 2017, May 2018), each with regular 0.2-12 km profiling through transecting the remote Pacific and Atlantic Ocean basins. Additional data are acquired also for the Southern Ocean and Artic basin, as well as two flights over Antarctica. ATom in situ measurements provide a near-complete chemical characterization of the ~140,000 10-second (80 m by 2 km) air parcels measured along the flight path. This paper presents the Modeling Data Stream (MDS), a continuous gap-filled record of the 10-s parcels containing the chemical species needed to initialize a gas-phase chemistry model for the budgets of tropospheric ozone and methane. Global 3D models have been used to calculate the Reactivity Data Stream RDS), which is comprised of the chemical reactivities (production and loss) for methane, ozone, and carbon monoxide, through 24-hour integration of the 10-s parcels. These parcels accurately sample tropospheric heterogeneity and allow us to partially deconstruct the spatial scales and variability that defines tropospheric chemistry from composition to reactions. This paper provides a first look and analysis of the up-to-date MDS and RDS data including all four deployments (Prather et al., 2023, doi: 10.7280/D1B12H). ATom's regular profiling of the ocean basins allows for weighted averages to build probability densities for key species and reactivities presented here. These statistics provide climatological metrics for global chemistry models, for example, the large-scale pattern of ozone and methane loss in the lower troposphere, and the more sporadic hot spots of ozone production in the upper troposphere. The profiling curtains of reactivity also identify meteorologically variable and hence deploymentspecific hot spots of photochemical activity. Added calculations of the sensitivities of the production and loss terms relative to each species emphasize the few dominant species that control the ozone and methane budgets, and whose statistical patterns should be key model-measurement metrics. From the sensitivities, we also derive linearized lifetimes of ozone and methane on a parcel-by-parcel basis and average over the basins, providing an observational basis for these previously model-only diagnostics. We had found that most model differences in the ozone and methane budgets are caused by the models calculating different climatologies for the key species such as O3, CO, H2O, NOx, CH4 plus T, and thus these ATom measurements provide a substantial contribution to the understanding of model differences and even identifying model errors in global tropospheric chemistry. [ABSTRACT FROM AUTHOR]

Extra‐tropical cyclones are a relevant feature in the climate at middle and high latitudes. Despite their importance, most studies typically focus only on cyclones identified at a single atmospheric level and on events close to the surface. This paper provides a new perspective on the Southern Hemisphere (SH) cyclone events based on the multilevel cyclone tracking algorithm STACKER. The algorithm, using relative vorticity, detects the raw tracks at single levels and objectively combines them to provide the 3D events and their evolutionary timeline. As a result, a 3D cyclone climatology, based on ECMWF Reanalysis ERA‐I data from 12 pressure levels in the troposphere and lowermost stratosphere is presented. To the best of our knowledge, this is the first analysis carried out throughout the troposphere and the lowermost extratropical/subpolar stratosphere in order to give a comprehensive picture of the cyclone events as physical entities throughout their lifetime. Cyclone properties analysed are track densities, translational velocity, vorticity and lifetimes. For the subtropical and extra‐tropical SH, results support many previous ideas about cyclone characteristics, but new insights are also obtained. A total of 58,231 multilevel cyclone events lasting at least 2 days were detected, with vertical structures spanning two or more levels. This means an average of 303 cyclone events of all types per month, between 2001 and 2017, disregarding seasonality. Results show that cyclones are most frequently detected at the lowest levels of 925 and 700 hPa. By considering that cyclonic systems can be grouped into families according to their vertical extent, results per month on average show that shallow systems are the most frequent events with approximately 248 systems detected, followed by 43 intermediary and 11 deep events. Shallow and deep systems have a large percentage of events with genesis at 925 and 700 hPa. Density statistics show that shallow events are present at all latitude ranges mostly poleward of 30°S with high‐ and medium‐intensities, while intermediate ones are mostly restricted to mid‐latitudes and deep events are mostly confined to sub‐polar and polar latitudes. Cyclones over Antarctica seem to be mostly intermediary and deep cyclones, with longer lifetimes and lower velocities. [ABSTRACT FROM AUTHOR]

Current chemistry climate models do not include polar emissions and chemistry of halogens. This work presents the first implementation of an interactive polar module into the very short‐lived (VSL) halogen version of the Community Atmosphere Model with Chemistry (CAM‐Chem) model. The polar module includes photochemical release of molecular bromine, chlorine, and interhalogens from the sea‐ice surface, and brine diffusion of iodine biologically produced underneath and within porous sea‐ice. It also includes heterogeneous recycling of inorganic halogen reservoirs deposited over fresh sea‐ice surfaces and snow‐covered regions. The polar emission of chlorine, bromine, and iodine reach approximately 32, 250, and 39 Gg/year for Antarctica and 33, 271, and 4 Gg/year for the Arctic, respectively, with a marked seasonal cycle mainly driven by sunlight and sea‐ice coverage. Model results are validated against polar boundary layer measurements of ClO, BrO, and IO, and satellite BrO and IO columns. This validation includes satellite observations of IO over inner Antarctica for which an iodine "leapfrog" mechanism is proposed to transport active iodine from coastal source regions to the interior of the continent. The modeled chlorine and bromine polar sources represent up to 45% and 80% of the global biogenic VSLCl and VSLBr emissions, respectively, while the Antarctic sea‐ice iodine flux is ~10 times larger than that from the Southern Ocean. We present the first estimate of the contribution of polar halogen emissions to the global tropospheric halogen budget. CAM‐Chem includes now a complete representation of halogen sources and chemistry from pole‐to‐pole and from the Earth's surface up to the stratopause. Plain Language Summary: We present the first implementation of an interactive polar module into the halogen version of the Community Atmosphere Model with Chemistry (CAM‐Chem) model with the intention of expanding the model applicability to the polar regions, besides its wide usage for atmospheric studies throughout the tropics and midlatitudes. The state‐of‐the‐art polar module considers full gas‐phase and heterogeneous inorganic chlorine, bromine, and iodine chemistry and sources, which add up to the organic halogen emissions from the ocean surface (the so‐called very short‐lived substances, VSL). The online sea‐ice halogen sources depend on the seasonal variation of different types of icy surfaces and the intensity of radiation reaching the polar surface. Our results indicate that the contribution of polar halogen sources represents between 45% and 80% of the global biogenic VSL chlorine and bromine emissions, respectively; and that the Antarctic iodine sea‐ice annual flux is ~10 times larger than the total iodine source arising from the Southern Ocean. This work provides, for the first time, quantitative estimates of the annual and seasonal flux strength of each halogen family from the Arctic and Antarctic, as well as their contribution to the global tropospheric halogen budget, highlighting the importance of including the contribution of polar tropospheric halogens in global chemistry‐climate models. Key Points: The contribution of polar sea‐ice sources to the global tropospheric halogen budget has been computed using the CAM‐Chem modelThe annual halogen flux from the sea‐ice surface represents between 45% and 80% of the global chloro‐ and bromo‐carbon oceanic VSL emissionsIn Antarctica, the annual iodine sea‐ice flux is ~10 times larger than the oceanic inorganic iodine source [ABSTRACT FROM AUTHOR]

Bromine chemistry plays an important role in tropospheric ozone depletion events in polar regions. Autocatalytic reactions lead to bromine explosion events, causing ozone depletion to near-zero levels in the polar troposphere. Bromine chemistry over Antarctica is not fully understood, and ground-based observations are scarce. This work presents year-long observations of bromine oxide (BrO) over the Bharati station (69.41°S, 76.19°E) using Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) from December 2018 to February 2020. The results show that elevated BrO mixing ratios were found during spring (September), with a maximum value of 10.21 ± 4.38 pptv for clear sky conditions and 33.15 ± 2.23 pptv for cloudy conditions. BrO was not observed above the detection limit (∼3 × 1013 molecule cm−2) outside spring on clear days. In general, lower mixing ratios were observed on clear days over Bharati compared to stations in West Antarctica. This indicates a different source strength over East Antarctica compared to West Antarctica. BrO vertical column densities were high during spring, with a maximum value of 1.34 ± 0.35 × 1014 molecule cm−2. The vertical profiles of the BrO mixing ratios show a peak at the surface during spring (average of 6.5 ± 1.91 pptv), decreasing sharply with altitude. Back trajectories show that air masses passing over the first year ice showed higher BrO, although factors such as meteorology play an important role in determining the absolute levels. Using a box model, we show that bromine chemistry can deplete as much as 2.15 ppb of ozone in a day at the Bharati Station on clear days, which shows that it does not lead to complete ozone depletion events over Bharati. • Year-long observations over Bharati, Antarctica, show elevated BrO only during spring, unlike other Antarctic Stations. • BrO values at Bharati are lower compared to stations in West Antarctic. • BrO levels were not sufficient to cause severe ozone depletion. [ABSTRACT FROM AUTHOR]

This article reports on satellite observations of iodine monoxide (IO) and bromine monoxide (BrO). The region of interest is Antarctica in the time between spring and autumn. Both molecules, IO and BrO, are reactive halogen species and strongly influence tropospheric composition. As a result, a better understanding of their spatial distribution and temporal evolution is necessary to assess accurately their role in tropospheric chemistry. Especially in the case of IO, information on its present magnitude, spatial distribution patterns and source regions is still sparse. The present study is based on six years of SCIAMACHY (Scanning Imaging Absorption spectro Meter for Atmospheric Cartography) data recorded in nadir viewing geometry. Multi-year averages of monthly mean IO columns are presented and compared to the distributions of BrO. Influences of the IO air mass factor and the IO absorption cross section temperature dependence on the absolute vertical columns are discussed. The long-term observations of IO and BrO columns yield new insight into the temporal and spatial variation of IO above the Antarctic region. The occurrence of IO on Antarctic sea ice in late spring (November) is discovered and presented. In addition, the comparison between IO and BrO distributions show many differences, which argues for different mechanisms and individual nature of the release of the two halogen oxide precursors. The state of the ecosystem, in particular the changing condition of the sea ice in late spring, is used to explain the observations of the IO behaviour over Antarctica and the differences between IO and BrO distributions. [ABSTRACT FROM AUTHOR]

The vertical distribution of nitric oxide (NO) was investigated by profiling from a tethered balloon platform during the 2003 Antarctic Tropospheric Chemistry Investigation (ANTCI) at South Pole (SP), Antarctica. The lower atmosphere was probed between the surface and 120m height by pulling air from an inlet attached to the balloon through a thin-wall, 135m-long Teflon sampling line and by analyzing NO in this airflow with a ground-borne monitor. Losses and conversion of NO during the 2–4-min residence time in the sampling line were on average on the order of 6–16%, providing a feasible approach for the measurement of vertical NO profiles under SP conditions. NO was found to be highly variable within the lowest 100m of the atmosphere. Greatly enhanced NO mixing ratios were constrained to a shallow (20–50m height) air layer nearest to the surface, above which NO rapidly dropped to its mixed boundary layer background levels. Concurrent measurements of ozone and meteorological conditions provide insight into linkages between the ongoing snowpack and boundary layer nitrogen oxides (NO x =NO+NO2) and ozone chemistry. Since [OH] and [HO2] are non-linearly coupled to absolute levels of NO x , their concentrations and the rate of ozone production are expected to similarly show appreciable changes on small vertical scales during conditions with enhanced [NO x ]. [Copyright &y& Elsevier]

The role of the vast Antarctic polar plateau in the global mercury cycle was previously relatively unknown. Here, for the first time, mercury concentrations in snow and air, combined with vertical flux measurements at the South Pole (November–December 2003 and November 2005) have provided considerable insight into the cycling of this element through the Antarctic environment. These insights include observations showing atmospheric oxidized mercury depositing to the snow pack, subsequent photoreduction, and emissions of gaseous elemental mercury from the snow pack. Oxidized mercury (e.g., reactive gaseous mercury and fine particulate mercury) showed high concentrations (100–1000pgm−3) in the near-surface air, with these concentrations strongly correlated with vertical mixing rates and showing rapid surface deposition. This suggests that the troposphere over Antarctica is enhanced in oxidized mercury, with mercury cycling between elemental and oxidized states, and between the atmosphere and snow pack. Based on these limited measurements at South Pole, we estimate that the Antarctic polar plateau could sequester as much as 60 metric tons of Hg annually. These data also suggest that there could be a seasonal cycling of atmospheric mercury oxidation, deposition, and re-emission via photoreduction of 490 metric tons annually. This cycling is restricted to the annual sunlit period and peaks 3–4 weeks after solar maximum. To our knowledge, these provisional values represent the first estimates of the mercury balance and cycling for the extensive Antarctic polar plateau. [Copyright &y& Elsevier]

As part of the Antarctic Tropospheric Chemistry Investigation (ANTCI), bulk aerosol-particle samples collected at the South Pole were analyzed for nitrate, sulfate, methanesulfonate (MSA), selected trace elements and radionuclides. The samples were collected in the same manner as in the Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) campaigns of 1998 and 2000. The ANTCI mean sulfate (124ngm−3) and MSA (9.1ngm−3) concentrations were comparable to those during ISCAT, but high MSA and sodium and high MSA/sulfate in late November/early December indicated pervasive maritime influences during that time. Trajectory analyses indicate that the Weddell Sea and the Southern Ocean near Wilkes Land were probable sources for the ocean-derived sulfate. The transport of marine air occurs mainly in the buffer layer or free troposphere, and the rapid oxidation of biogenic sulfur to SO2 appears to be the basis for the observed low MSA/sulfate ratios. Elements typically associated with mineral dust (Al, Fe, K) and other elements with continental sources (Pb, Sb, Zn) had higher concentrations during ANTCI than ISCAT. The mean filterable nitrate (f-NO3 −) concentration (280ngm−3) also was conspicuously higher than during ISCAT (39 and 150ngm−3). Several peaks in f-NO3 − were synchronous with those for MSA and sulfate, but some samples had high f-NO3 − but neither high MSA nor sulfate. While there is some evidence that nitrate or nitric acid is transported to SP from distant sources, local emissions of nitrogen oxides from the snow are a far more important source overall. [Copyright &y& Elsevier]

Vertical boundary-layer ozone profiles were measured from a tethered balloon platform during the 2003 Antarctic Tropospheric Chemistry Investigation (ANTCI) at South Pole Station, Antarctica. Electrochemical concentration cell (ECC) ozonesondes were used in obtaining 128 ascent and descent profile measurements to about 500m height during 13–30 December 2003. Various data checks and intercomparisons were done to confirm the accuracy of the ozonesondes. The ozonesondes compared well to a surface ozone ultra-violet (UV) absorption monitor located next to the tether balloon site. During the 18-day period, ozonesonde measurement checks at the surface averaged 0.2±1.0ppbv higher than the continuous ozone measurements under ambient concentrations ranging from 18 to 51ppbv. This agreement was also consistent when compared to the nearby NOAA UV-monitor sampling at 17m above ground level during well-mixed conditions near the surface. In addition to the single ECC sonde profiles, five dual ECC ozonesondes were run on the tether platform. Four release balloon-borne ozonesondes were also launched during the project. Under very sharp ozone gradient events, the release ozonesonde (with a rise rate of ∼4–6ms−1) passed through the gradient layer too quickly to capture the detail as measured by the controlled tethersonde at ∼0.3ms−1 ascent/descent rate. Another method of ozone profiling was also done utilizing the UV monitor at the tether site and a 135-m-long Teflon sampling line with a sampling inlet mounted to and raised with the tethered balloon. The ECC ozonesonde averaged about 0.7±0.8ppbv lower than the long-line sampling method from eight profiles. [Copyright &y& Elsevier]

This paper focuses on the use of an acoustic sounder, or sodar, during the 2003 Antarctic Tropospheric Chemistry Investigation (ANTCI), to document the behavior of very shallow (<50m) stable boundary layers thought to be one of the critical factors for explaining the very high levels of nitric oxide (NO) found in past field experiments at the South Pole. The use of a tethered balloon, profiling wind, temperature, NO, and ozone provided for a detailed interpretation of sodar data for the period 12–30 December 2003. For the same period, sonic anemometer 2-m turbulence measurements, averaged to 0.5h, linked surface processes to the evolution of the boundary layer in response to changing radiative balance and synoptic weather changes. A mixing-layer detection method was developed and applied to half-hour average sodar amplitude profiles for the period 23 November–30 December 2003. These data also allowed for testing of simple diagnostic equations for the mixing-layer depth as well as estimates of vertical diffusion rates under stable conditions, the latter being important for the effective depth of the mixing layer vis-à-vis the nonlinear NO chemistry postulated from earlier analyses. With the extended sampling period, two sub-seasonal regimes were examined: (1) a late-December period, with the full suite of supporting measurements, where the earlier results that shallow mixing layers associated with light winds and strong surface stability can be among the dominant factors leading to high NO levels were repeated and (2) a late November period that revealed additional complexities with very high NO concentrations appearing at times in concert with higher winds, weaker surface stability, and deeper mixing layers. The latter results are only consistent with a more complicated picture of how NO can build to very high levels that involves invoking the previously expressed dependence of elevated NO levels on nonlinear NO x (NO x =NO+NO2) chemistry, greater fluxes of NO x from the snowpack than previously observed at the South Pole, and the potential for enhanced NO x accumulation effects involving air parcels draining off the high plateau. The results of ANTCI from 2003 thus argue for more complete future observations of boundary layer conditions over the high Antarctic Plateau and determination of the spatial and temporal variability of snow nitrate concentrations over the high plateau and their relation to NO recycling and the snow accumulation/ablation/erosion cycle. [Copyright &y& Elsevier]

Vertical profile measurements of ozone, water vapor, and meteorological conditions, as well as surface and tower measurements of these parameters during the 2003 Antarctic Tropospheric Chemistry Investigation (ANTCI) yielded their vertical (between the surface and 500m) and temporal distribution in the boundary layer at South Pole (SP) during December 13–30, 2003. Ozone in the surface and lower planetary boundary layer above SP was frequently enhanced over lower free tropospheric levels. During stable atmospheric conditions (which typically existed during low wind and fair sky conditions) ozone accumulated in the surface layer to reach up to twice its background concentration. These conditions were correlated with air transport from the N–SE sector, when air flowed downslope from the Antarctic plateau towards the SP. These data provide further insight into the vigorous photochemistry and ozone production that result from the highly elevated levels of nitrogen oxides (NO x ) in the Antarctic surface layer. [Copyright &y& Elsevier]

The Antarctic Tropospheric Chemistry Investigation (ANTCI) was carried out from late November to December 2003 with both extended ground-based and tethered balloon studies at Amundsen Scott Station, South Pole. ANTCI 2003 was the first of two Antarctic field studies with the primary goal of further exploring the active photochemistry of the South Pole region that was first identified in the previous Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program. Since ISCAT was fully ground-based, ANTCI 2003 goals included expanding chemical studies both vertically upward to investigate mixing and horizontally to better understand large-scale plateau NO x production and transport. Thus, in addition to ground-based experiments at South Pole, Twin Otter aircraft sampling took place out to hundreds of kilometers in several directions from the South Pole. These were designed to specifically address the issue of how representative past South Pole chemical measurements are of the surrounding high plateau region. The Twin Otter was also used to make transects along the coast both north and south of McMurdo Station. The present paper summarizes the overall setting and results of this investigation and highlights the many new findings that were obtained. [Copyright &y& Elsevier]

Earlier reports show very low concentrations of phosphine in remote air of the lower troposphere of nonpolar regions, in the low ng m-3 range during the night and in the pg m-3 range during daylight around noon. In this study, abnormally and unexpectedly high phosphine concentrations (30.0–407.8 ng m-3, 11 locations) were found in polar air samples collected on Millor Peninsula, eastern Antarctica and Fildes Peninsula, western Antarctica. The maximum concentration was measured in the atmosphere of penguin colonies. Field phosphine emission rates from four colonies were 8.99 ng m-2 h-1 (skua colony), 9.56 ng m-2 h-1 (gentoo penguin colony), 39.96 ng m-2 h-1 (seal colony) and 63.58 ng m-2 h-1 (empire penguin colony), respectively. Our air sampling sites are located downwind of two large penguin colonies, indicating that penguin colony emission is the predominant source for atmospheric PH3 on Millor Peninsula. Laboratory scale incubation of ornithogenic soils amended by penguin guanos yielded a maximum PH3 production rate of 0.58 ng kg-1 d-1 specifically at low temperature (4 °C). Significant concentrations of phosphine occur in the atmosphere of coastal Antarctica and confirm the existence of a small gaseous link in the phosphorus cycle of the Antarctic tundra ecosystem. [ABSTRACT FROM AUTHOR]