Sulfur hexafluoride (SF6) is a greenhouse gas with one of the highest radiative efficiencies in the atmosphere as well as an important indicator of transport time scales in the stratosphere. The ...current widely used estimate of the atmospheric lifetime of SF6 is 3200 years. In this study we use in situ measurements in the 2000 Arctic polar vortex that sampled air with up to 50% SF6 loss to calculate an SF6 lifetime. Comparison of these measurements with output from the Whole Atmosphere Community Climate Model (WACCM) shows that WACCM transport into the vortex is accurate and that an important SF6 loss mechanism, believed to be electron attachment, is missing in the model. Based on the measurements and estimates of the size of the vortex, we calculate an SF6 lifetime of 850 years with an uncertainty range of 580–1400 years. The amount of SF6 loss is shown to be consistent with that of HFC‐227ea, which has a lifetime of 670–780 years, adding independent support to our new SF6 lifetime estimate. Based on the revised lifetime the global warming potential of SF6 will decrease only slightly for short time horizons (<100 years) but will decrease substantially for time horizons longer than 2000 years. Also, the use of SF6 measurements as an indicator of transport time scales in the stratosphere clearly must account for potential influence from polar vortex air.
Key Points
Atmospheric lifetime of SF6 reduced by nearly a factor of 3 based on measurements in the stratospheric polar vortex
Consistency of SF6 and HFC‐227ea derived mean age of air gives independent confirmation of SF6 lifetime reduction
The signal of mesospheric loss or production of a trace gas is highly concentrated in the stratospheric polar vortices each winter
Plain Language Summary
We have calculated an atmospheric lifetime of the molecule SF6 based on trace gas measurements in the stratospheric polar vortex. This lifetime is 3 times shorter than the commonly used lifetime over the past 20 years. Since SF6 is a greenhouse gas this adjustment has implications for long‐term climate effects.
Purpose
The purpose was to review relevant scientific papers written since 1989 which focused on the prevalence and management of dysgeusia as an oral side effect of cancer treatment.
Methods
Our ...literature search was limited to English language papers published between 1990 and 2008. A total of 30 papers were reviewed; the results of 26 of these papers were included in the present systematic review. A structured assessment form was used by two reviewers for each paper. Studies were weighted as to the quality of the study design, and treatment recommendations were based on the relative strength of each paper.
Results
A wide range in reported prevalence of dysgeusia was identified with the weighted prevalence from 56–76%, depending on the type of cancer treatment. Attempts to prevent dysgeusia through the prophylactic use of zinc sulfate or amifostine have been of limited benefit. Nutritional counseling may be helpful to some patients in minimizing the symptoms of dysgeusia.
Conclusions
Dysgeusia is a common oral side effect of cancer therapy (radiotherapy, chemotherapy, or combined modality therapy) and often impacts negatively on quality of life. From the current literature, there does not appear to be a predictable way of preventing or treating dysgeusia.
HCFC-22 (CHClF ₂) and HFC-134a (CH ₂FCF ₃) are two major gases currently used worldwide in domestic and commercial refrigeration and air conditioning. HCFC-22 contributes to stratospheric ozone ...depletion, and both species are potent greenhouse gases. In this work, we study in situ observations of HCFC-22 and HFC-134a taken from research aircraft over the Pacific Ocean in a 3-y span HIaper-Pole-to-Pole Observations (HIPPO) 2009–2011 and combine these data with long-term ground observations from global surface sites National Oceanic and Atmospheric Administration (NOAA) and Advanced Global Atmospheric Gases Experiment (AGAGE) networks. We find the global annual emissions of HCFC-22 and HFC-134a have increased substantially over the past two decades. Emissions of HFC-134a are consistently higher compared with the United Nations Framework Convention on Climate Change (UNFCCC) inventory since 2000, by 60% more in recent years (2009–2012). Apart from these decadal emission constraints, we also quantify recent seasonal emission patterns showing that summertime emissions of HCFC-22 and HFC-134a are two to three times higher than wintertime emissions. This unforeseen large seasonal variation indicates that unaccounted mechanisms controlling refrigerant gas emissions are missing in the existing inventory estimates. Possible mechanisms enhancing refrigerant losses in summer are ( i ) higher vapor pressure in the sealed compartment of the system at summer high temperatures and ( ii ) more frequent use and service of refrigerators and air conditioners in summer months. Our results suggest that engineering (e.g., better temperature/vibration-resistant system sealing and new system design of more compact/efficient components) and regulatory (e.g., reinforcing system service regulations) steps to improve containment of these gases from working devices could effectively reduce their release to the atmosphere.
Significance HCFC-22 (CHClF ₂) and HFC-134a (CH ₂FCF ₃) are two major gases currently used worldwide in domestic and commercial refrigeration and air conditioning. HCFC-22 contributes to stratospheric ozone depletion, and both species are potent greenhouse gases. We find pronounced seasonal variations of global emissions for these two major refrigerants, with summer emissions two to three times higher than in winter. Thus results suggest that global emissions of these potent greenhouse gases might be mitigated by improved design and engineering of refrigeration systems and/or by reinforcing system service regulations.
Peroxyacetyl nitrate (PAN) is produced in the atmosphere by photochemical oxidation of non-methane volatile organic compounds in the presence of nitrogen oxides (NO x ), and it can be transported ...over long distances at cold temperatures before decomposing thermally to release NO x in the remote troposphere. It is both a tracer and a precursor for transpacific ozone pollution transported from East Asia to North America. Here, we directly demonstrate this transport with PAN satellite observations from the infrared atmospheric sounding interferometer (IASI). We reprocess the IASI PAN retrievals by replacing the constant prior vertical profile with vertical shape factors from the GEOS-Chem model that capture the contrasting shapes observed from aircraft over South Korea (KORUS-AQ) and the North Pacific (ATom). The reprocessed IASI PAN observations show maximum transpacific transport of East Asian pollution in spring, with events over the Northeast Pacific offshore from the Western US associated in GEOS-Chem with elevated ozone in the lower free troposphere. However, these events increase surface ozone in the US by less than 1 ppbv because the East Asian pollution mainly remains offshore as it circulates the Pacific High.
In this study we reexamine nearly four decades of in situ balloon‐based stratospheric observations of SF6 and CO2 with an idealized model and reanalysis products. We use new techniques to account for ...the spatial and temporal inhomogeneity of the sparse balloon profiles and to calculate stratospheric mean ages of air more consistently from the observations with the idealized model. By doing so we are able to more clearly show and account for the variability of mean age of air throughout the bulk of the depth of the stratosphere. From an idealized model guided by the observations, we identify variability in the mean age due to the seasonal cycle of stratospheric transport, the quasi‐biennial oscillation in tropical zonal winds, major volcanic eruptions, and linear trends that vary significantly with altitude. We calculate a negative mean age trend in the lowest 5 km of the stratosphere that agrees within uncertainties with a trend calculated from a set of chemistry climate model mean ages in this layer. The mean age trends reverse sign in the middle and upper stratosphere and are in agreement with a previous positive trend estimate using the same observational data set, although we have substantially reduced the uncertainty on the trend. Our analysis shows that a long time series of in situ profile measurements of trace gases such as SF6 and CO2 can be a unique and useful indicator of stratospheric circulation variability on a range of time scales and an important contributor to help validate the stratospheric portion of global chemistry climate models. However, with only SF6 and CO2 measurements, the competing effects on mean age between mean circulation and mixing (tropical entrainment) are not uniquely separable.
Key Points
Refined calculation of stratospheric mean age of air trendsMean ages have decreased in the lower stratosphere and increased in the middle stratosphereTrace gas measurements are a useful indicator of stratosphere circulation changes
National-scale emissions of carbon tetrachloride (CCl₄) are derived based on inverse modeling of atmospheric observations at multiple sites across the United States from the National Oceanic and ...Atmospheric Administration’s flask air sampling network. We estimate an annual average US emission of 4.0 (2.0–6.5) Gg CCl₄ y−1 during 2008–2012, which is almost two orders of magnitude larger than reported to the US Environmental Protection Agency (EPA) Toxics Release Inventory (TRI) (mean of 0.06 Gg y−1) but only 8% (3–22%) of global CCl₄ emissions during these years. Emissive regions identified by the observations and consistently shown in all inversion results include the Gulf Coast states, the San Francisco Bay Area in California, and the Denver area in Colorado. Both the observation-derived emissions and the US EPA TRI identified Texas and Louisiana as the largest contributors, accounting for one- to two-thirds of the US national total CCl₄ emission during 2008–2012. These results are qualitatively consistent with multiple aircraft and ship surveys conducted in earlier years, which suggested significant enhancements in atmospheric mole fractions measured near Houston and surrounding areas. Furthermore, the emission distribution derived for CCl₄ throughout the United States is more consistent with the distribution of industrial activities included in the TRI than with the distribution of other potential CCl₄ sources such as uncapped landfills or activities related to population density (e.g., use of chlorine-containing bleach).
Ozone is a key constituent of the troposphere, where it drives photochemical processes, impacts air quality, and acts as a climate forcer. Large-scale in situ observations of ozone commensurate with ...the grid resolution of current Earth system models are necessary to validate model outputs and satellite retrievals. In this paper, we examine measurements from the Atmospheric Tomography (ATom; four deployments in 2016–2018) and the HIAPER Pole-to-Pole Observations (HIPPO; five deployments in 2009–2011) experiments, two global-scale airborne campaigns covering the Pacific and Atlantic basins.
ATom and HIPPO represent the first global-scale, vertically resolved measurements of O3 distributions throughout the troposphere, with HIPPO sampling the atmosphere over the Pacific and ATom sampling both the Pacific and Atlantic. Given the relatively limited temporal resolution of these two campaigns, we first compare ATom and HIPPO ozone data to longer-term observational records to establish the representativeness of our dataset. We show that these two airborne campaigns captured on average 53 %, 54 %, and 38 % of the ozone variability in the marine boundary layer, free troposphere, and upper troposphere–lower stratosphere (UTLS), respectively, at nine well-established ozonesonde sites. Additionally, ATom captured the most frequent ozone concentrations measured by regular commercial aircraft flights in the northern Atlantic UTLS. We then use the repeated vertical profiles from these two campaigns to confirm and extend the existing knowledge of tropospheric ozone spatial and vertical distributions throughout the remote troposphere. We highlight a clear hemispheric gradient, with greater ozone in the Northern Hemisphere, consistent with greater precursor emissions and consistent with previous modeling and satellite studies. We also show that the ozone distribution below 8 km was similar in the extra-tropics of the Atlantic and Pacific basins, likely due to zonal circulation patterns. However, twice as much ozone was found in the tropical Atlantic as in the tropical Pacific, due to well-documented dynamical patterns transporting continental air masses over the Atlantic. Finally, we show that the seasonal variability of tropospheric ozone over the Pacific and the Atlantic basins is driven year-round by transported continental plumes and photochemistry, and the vertical distribution is driven by photochemistry and mixing with stratospheric air. This new dataset provides additional constraints for global climate and chemistry models to improve our understanding of both ozone production and loss processes in remote regions, as well as the influence of anthropogenic emissions on baseline ozone.
We use a modified version of the tropical leaky pipe (TLP) model of the stratosphere to explore how well an idealized model can (1) reproduce global chemistry‐climate model (CCM) output and (2) ...constrain transport characteristics necessary to replicate measurements of long‐lived trace gases. The version of the TLP model we use includes the simulation of long‐lived trace gases, such as SF6 and CO2, as well as photochemically active trace gases such as CFC‐11, CFC‐12, and N2O. The TLP model was found to accurately replicate trace gas output from the Canadian Middle Atmosphere Model (CMAM) for time‐averaged profiles in the tropics and each extratropical region. Given confidence that the TLP model represents the basic transport features in CMAM we then used the TLP model to interpret differences between CMAM output and measurements from the Atmospheric Chemistry Experiment and balloons. The TLP model is shown to uniquely determine residual mean circulation and recirculation (mixing between the extratropics and tropics) changes necessary for CMAM to more accurately simulate the measurements. Such guidance on these transport parameters is novel due to the relatively high precision and the simultaneous derivation of important parameters, as compared to previous studies. The TLP model can ideally be used as a bridge between measurements and CCMs to potentially allow more targeted modification of the CCMs than would otherwise be possible.
Key Points
Idealized stratospheric model accurately simulates CMAM trace gas and mean age profiles
Idealized model provides quantitative transport guidance for CCM to better simulate observations
Specific suite of trace gas measurements provides unique transport information to validate CCMs
Abstract This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling ...campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The stratospheric inorganic bromine (Bry) burden arising from the degradation of brominated very short-lived organic substances (VSLorg) and its partitioning between reactive and reservoir species is ...needed for a comprehensive assessment of the ozone depletion potential of brominated trace gases. Here we present modeled inorganic bromine abundances over the Pacific tropical tropopause based on aircraft observations of VSLorg from two campaigns of the Airborne Tropical TRopopause EXperiment (ATTREX 2013, carried out over the eastern Pacific, and ATTREX 2014, carried out over the western Pacific) and chemistry-climate simulations (along ATTREX flight tracks) using the specific meteorology prevailing. Using the Community Atmosphere Model with Chemistry (CAM-Chem) we model that BrO and Br are the daytime dominant species. Integrated across all ATTREX flights, BrO represents ∼ 43 and 48 % of daytime Bry abundance at 17 km over the western and eastern Pacific, respectively. The results also show zones where Br / BrO > 1 depending on the solar zenith angle (SZA), ozone concentration, and temperature. On the other hand, BrCl and BrONO2 were found to be the dominant nighttime species with ∼ 61 and 56 % of abundance at 17 km over the western and eastern Pacific, respectively. The western-to-eastern differences in the partitioning of inorganic bromine are explained by different abundances of ozone (O3), nitrogen dioxide (NO2), total inorganic chlorine (Cly), and the efficiency of heterogeneous reactions of bromine reservoirs (mostly BrONO2 and HBr) occurring on ice crystals.
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