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Approximately half of the carbon dioxide (CO 2) released annually by the combustion of fossil fuels stays in the atmosphere (Friedlingstein et al., 2022; Keeling et al., 1976; Schimel et al., 2001). The remaining CO 2 is taken up by the terrestrial biosphere and ocean in roughly equal proportions (Keeling & Manning, 2014; Khatiwala et al., 2009; Sabine et al., 2004). The efficiency of the ocean and land sinks varies with both climate and atmospheric CO 2 , representing an important feedback in the climate system (e.g., Ballantyne et al., 2012

22 pags., 11 figs., 2 tabs. -- Open Access funded by Creative Commons Atribution Licence 4.0, Halogenated very short lived substances (VSLS) affect the ozone budget in the atmosphere. Brominated VSLS are naturally emitted from the ocean, and current oceanic emission inventories vary dramatically. We present a new global oceanic emission inventory of Br‐VSLS (bromoform and dibromomethane), considering the physical forcing in the ocean and the atmosphere, as well as the ocean biogeochemistry control. A data‐oriented machine‐learning emulator was developed to couple the air‐sea exchange with the ocean biogeochemistry. The predicted surface seawater concentrations and the surface atmospheric mixing ratios of Br‐VSLS are evaluated with long‐term, global‐scale observations; and the predicted vertical distributions of Br‐VSLS are compared to the global airborne observations in both boreal summer and winter. The global marine emissions of bromoform and dibromomethane are estimated to be 385 and 54 Gg Br per year, respectively. The new oceanic emission inventory of Br‐VSLS is more skillful than the widely used top‐down approaches for representing the seasonal/spatial variations and the annual means of atmospheric concentrations. The new approach improves the model predictability for the coupled Earth system model and can be used as a basis for investigating the past and future ocean emissions and feedbacks under climate change. This model framework can be used to calculate the bidirectional oceanic fluxes for other compounds of interest., S.‐Y. W. is supported by the NCAR Advanced Study Program (ASP) Postdoctoral Fellowship. The CESM project is supported primarily by the National Science Foundation (NSF). This material is based upon work supported by NCAR, which is a major facility sponsored by the NSF under Cooperative Agreement 1852977. The computing and data storage resources, including the Cheyenne supercomputer (doi:10.5065/D6RX99HX), were provided by the Computational and Information Systems Laboratory (CISL) at NCAR. The Atmospheric Tomography Mission (ATom) is funded by the Earth Science Project Office at NASA (NNX15AJ23G). The NOAA ground‐based measurements were supported in part by NOAA's Atmospheric Chemistry, Carbon Cycle and Climate Program of its Climate Program Office. NASA's ATom mission was funded as a NASA Earth Science Venture ‐ suborbital mission. We thank NASA ESPO, the NASA DC‐8 crew, and the ATom Science Team for their exceptional professionalism in support of this mission. Franziska Ziska (GEOMAR, Germany) and colleagues are acknowledged for compiling the HalOcAt data set. Tomás Sherwen (University of York, UK) and Britton Stephens (NCAR, USA) are acknowledged for helpful discussions. CAM‐chem is a component of the NCAR CESM which is publicly available on the project website (http://www.cesm. ucar.edu/). The HalOcAt data set used for the training of the machine‐learning emulator is available in Ziska et al. (doi: https://doi.org/10.5194/acp‐13‐8915‐ 2013). The NCAR CESM Large Ensemble data set is available from the project website (http://www.cesm.ucar. edu/projects/community‐projects/ LENS/). The NCAR TOGA, UCI WAS, and NOAA PFP measurements during the NASA ATom campaign is available from Wofsy et al. (2018).

International audience; We present observations of local enhancements in carbon dioxide (CO2) from local emissions sources over three eastern US regions during four deployments of the Atmospheric Carbon TransportAmerica (ACT-America) campaign between summer 2016 and spring 2018. Local CO2 emissions werecharacterized by carbon monoxide (CO) to CO2 enhancement ratios (i.e., ΔCO/ΔCO2 ) in air mass mixing observed during aircraft transects within the planetary boundary layer. By analyzing regional-scale variability of CO2 enhancements as a function of ΔCO/ΔCO2 enhancement ratios, observed relative contributions to CO2 emissions were separated into fossil fuel and biomass burning (BB) regimes across regions and seasons. CO2 emission contributions attributed to biomass burning (ΔCO/ΔCO2 > 4%) were negligible during summer and fall in all regions but climbed to ∼9%–11% of observed combustion contributions in the South during winter and spring. Relative CO2 fire emission trends matched observed winter and spring BB contributions,but conflictingly predicted similar levels of BB during the fall. Satellite fire data from MODIS and VIIRS suggested the use of higher spatial resolution fire data that might improve modeled BB emissions but were not able to explain the bulk of the discrepancy

Urban emissions remain an underexamined part of the methane budget. Here we present and interpret aircraft observations of six old and leak‐prone major cities along the East Coast of the United States. We use direct observations of methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), ethane (C2H6), and their correlations to quantify CH4 emissions and attribute to natural gas. We find the five largest cities emit 0.85 (0.63, 1.12) Tg CH4/year, of which 0.75 (0.49, 1.10) Tg CH4/year is attributed to natural gas. Our estimates, which include all thermogenic methane sources including end use, are more than twice that reported in the most recent gridded EPA inventory, which does not include end‐use emissions. These results highlight that current urban inventory estimates of natural gas emissions are substantially low, either due to underestimates of leakage, lack of inclusion of end‐use emissions, or some combination thereof., Key Points Aircraft observations downwind of six major cities along the U.S. East Coast are used to estimate urban methane emissionsObserved urban methane estimates are about twice that reported in the Gridded EPA inventoryMethane emissions from natural gas (including end use) in five cities combined exceeds nationwide emissions estimate from local distribution

Author(s): Lan, X; Tans, P; Sweeney, C; Andrews, A; Dlugokencky, E; Schwietzke, S; Kofler, J; McKain, K; Thoning, K; Crotwell, M; Montzka, S; Miller, BR; Biraud, SC | Abstract: Recent studies show conflicting estimates of trends in methane (CH4) emissions from oil and natural gas (ONG) operations in the United States. We analyze atmospheric CH4 measurements from 20 North American sites in the National Oceanic and Atmospheric Administration Global Greenhouse Gas Reference Network and determined trends for 2006–2015. Using CH4 vertical gradients as an indicator of regional surface emissions, we find no significant increase in emissions at most sites and modest increases at three sites heavily influenced by ONG activities. Our estimated increases in North American ONG CH4 emissions (on average approximately 3.4 ± 1.4 %/year for 2006–2015, ±σ) are much smaller than estimates from some previous studies and below our detection threshold for total emissions increases at the east coast sites that are sensitive to U.S. outflows. We also find an increasing trend in ethane/methane emission ratios, which has resulted in major overestimation of oil and gas emissions trends in some previous studies.

Earth's atmosphere oxidizes the greenhouse gas methane and other gases, thus determining their lifetimes and oxidation products. Much of this oxidation occurs in the remote, relatively clean free troposphere above the planetary boundary layer, where the oxidation chemistry is thought to be much simpler and better understood than it is in urban regions or forests. The NASA airborne Atmospheric Tomography study (ATom) was designed to produce cross sections of the detailed atmospheric composition in the remote atmosphere over the Pacific and Atlantic Oceans during four seasons. As part of the extensive ATom data set, measurements of the atmosphere's primary oxidant, hydroxyl (OH), and hydroperoxyl (HO₂) are compared to a photochemical box model to test the oxidation chemistry. Generally, observed and modeled median OH and HO₂ agree to with combined uncertainties at the 2σ confidence level, which is ~±40%. For some seasons, this agreement is within ~±20% below 6 km altitude. While this test finds no significant differences, OH observations increasingly exceeded modeled values at altitudes above 8 km, becoming ~35% greater, which is near the combined uncertainties. Measurement uncertainty and possible unknown measurement errors complicate tests for unknown chemistry or incorrect reaction rate coefficients that would substantially affect the OH and HO₂ abundances. Future analysis of detailed comparisons may yield additional discrepancies that are masked in the median values.

©2017. American Geophysical Union. All Rights Reserved. Ozone depleting substances (ODSs) controlled by the Montreal Protocol are potent greenhouse gases (GHGs), as are their substitutes, the hydrofluorocarbons (HFCs). Here we provide for the first time a comprehensive estimate of U.S. emissions of ODSs and HFCs based on precise measurements in discrete air samples from across North America and in the remote atmosphere. Derived emissions show spatial and seasonal variations qualitatively consistent with known uses and largely confirm U.S. Environmental Protection Agency (EPA) national emissions inventories for most gases. The measurement-based results further indicate a substantial decline of ODS emissions from 2008 to 2014, equivalent to ~50% of the CO2-equivalent decline in combined emissions of CO2and all other long-lived GHGs inventoried by the EPA for the same period. Total estimated CO2-equivalent emissions of HFCs were comparable to the sum of ODS emissions in 2014, but can be expected to decline in the future in response to recent policy measures.

The anthropogenic CO2 accumulation rate for the Pacific Ocean was estimated from the decrease in δ13C of the dissolved inorganic carbon measured on six World Ocean Circulation Experiment cruises during the 1990s and repeated during Climate Variability and Predictability in the 2000s. A mean depth-integrated anthropogenic δ13C change of −83 ± 20‰ m decade−1 was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic δ13C decreases occurred between 40°S and 60°S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO2 accumulation rate of 0.41 ± 0.13 mol C m−2 yr−1 (0.82 ± 0.26 Pg C yr−1) was determined based on observed δ13C changes and is in agreement with previous observation- and model-based estimates. The mean dissolved inorganic carbon DIC13 inventory change of −178 ± 43‰ mol m−2 decade−1 was primarily the result of air-sea CO2 exchange acting on the measured air-sea δ13C disequilibrium of ~ −1.2 ± 0.1‰. Regional differences between the DIC13 inventory change and air-sea 13CO2 flux yielded net anthropogenic CO2 uptake rates (independent of ΔpCO2) that ranged from ~0 to 1 mol m−2 yr−1 and basin-wide mean of 1.2 ± 1.5 Pg C yr−1. High rates of surface ocean DIC increase and δ13C decrease observed in the Drake Passage (53°S–60°S) support above average anthropogenic CO2 accumulation since 2005. Observed δ13C changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO2 distribution and illustrate the utility of δ13C as a tracer to unravel the processes controlling the present and future accumulation of anthropogenic CO2 in the ocean.

Methane (CH4) fluxes from Alaska and other arctic regions may be sensitive to thawing permafrost and future climate change, but estimates of both current and future fluxes from the region are uncertain. This study estimates CH4 fluxes across Alaska for 2012-2014 using aircraft observations from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) and a geostatistical inverse model (GIM). We find that a simple flux model based on a daily soil temperature map and a static map of wetland extent reproduces the atmospheric CH4 observations at the state-wide, multi-year scale more effectively than global-scale, state-of-the-art process-based models. This result points to a simple and effective way of representing CH4 flux patterns across Alaska. It further suggests that contemporary process-based models can improve their representation of key processes that control fluxes at regional scales, and that more complex processes included in these models cannot be evaluated given the information content of available atmospheric CH4 observations. In addition, we find that CH4 emissions from the North Slope of Alaska account for 24% of the total statewide flux of 1.74 ± 0.44 Tg CH4 (for May-Oct.). Contemporary global-scale process models only attribute an average of 3% of the total flux to this region. This mismatch occurs for two reasons: process models likely underestimate wetland area in regions without visible surface water, and these models prematurely shut down CH4 fluxes at soil temperatures near 0°C. As a consequence, wetlands covered by vegetation and wetlands with persistently cold soils could be larger contributors to natural CH4 fluxes than in process estimates. Lastly, we find that the seasonality of CH4 fluxes varied during 2012-2014, but that total emissions did not differ significantly among years, despite substantial differences in soil temperature and precipitation; year-to-year variability in these environmental conditions did not affect obvious changes in total CH4 fluxes from the state.

We investigate the role of mesoscale eddies in modulating air-sea CO2 flux and associated biogeochemical fields in Drake Passage using in situ observations and an eddy-resolving numerical model. Both observations and model show a negative correlation between temperature and partial pressure of CO2 (pCO2) anomalies at the sea surface in austral summer, indicating that warm/cold anticyclonic/cyclonic eddies take up more/less CO2. In austral winter, in contrast, relationships are reversed: warm/cold anticyclonic/cyclonic eddies are characterized by a positive/negative pCO2 anomaly and more/less CO2 outgassing. It is argued that DIC-driven effects on pCO2 are greater than temperature effects in austral summer, leading to a negative correlation. In austral winter, however, the reverse is true. An eddy-centric analysis of the model solution reveals that nitrate and iron respond differently to the same vertical mixing: vertical mixing has a greater impact on iron because its normalized vertical gradient at the base of the surface mixed layer is an order of magnitude greater than that of nitrate. This article is protected by copyright. All rights reserved.

The measured 14C:12C isotopic ratio of atmospheric CO2 (and its associated derived Δ14C value) is an ideal tracer for determination of the fossil fuel derived CO2 enhancement contributing to any atmospheric CO2 measurement (Cff ). Given enough such measurements, independent top-down estimation of US fossil fuel-CO2 emissions should be possible. However, the number of Δ14C measurements is presently constrained by cost, available sample volume, and availability of mass spectrometer measurement facilities. Δ14C is therefore measured in just a small fraction of samples obtained by ask air sampling networks around the world. Here, we develop a Projection Pursuit Regression (PPR) model to predict Cff as a function of multiple surrogate gases acquired within the NOAA/ESRL Global Greenhouse Gas Reference Network (GGGRN). The surrogates consist of measured enhancements of various anthropogenic trace gases, including CO, SF6, and halo- and hydrocarbons acquired in vertical airborne sampling profiles near Cape May, NJ and Portsmouth, NH from 2005 through 2010. Model performance for these sites is quantified based on predicted values corresponding to test data excluded from the model building process. Chi-square hypothesis test analysis indicates that these predictions and corresponding observations are consistent given our uncertainty budget which accounts for random effects and one particular systematic effect. However, quantification of the combined uncertainty of the prediction due to all relevant systematic effects is difficult because of the limited range of the observations and their relatively high fractional uncertainties at the sampling sites considered here. To account for the possibility of additional systematic effects, we incorporate another component of uncertainty into our budget. Expanding the number of Δ14C measurements in the NOAA GGGRN and building new PPR models at additional sites would improve our understanding of uncertainties and potentially increase the number of Cff estimates by approximately a factor of three. Provided that these estimates are of comparable quality to Δ14C-based estimates, we expect an improved determination of fossil fuel-CO2 emissions.

Continuous measurements of atmospheric methane (CH4) mole fractions measured by NOAA's Global Greenhouse Gas Reference Network in Barrow, AK (BRW), show strong enhancements above background values when winds come from the land sector from July to December from 1986 to 2015, indicating that emissions from arctic tundra continue through autumn and into early winter. Twenty-nine years of measurements show little change in seasonal mean land sector CH4 enhancements, despite an increase in annual mean temperatures of 1.2 ± 0.8°C/decade (2σ). The record does reveal small increases in CH4 enhancements in November and December after 2010 due to increased late-season emissions. The lack of significant long-term trends suggests that more complex biogeochemical processes are counteracting the observed short-term (monthly) temperature sensitivity of 5.0 ± 3.6 ppb CH4/°C. Our results suggest that even the observed short-term temperature sensitivity from the Arctic will have little impact on the global atmospheric CH4 budget in the long term if future trajectories evolve with the same temperature sensitivity.

We present in situ airborne measurements of methane (CH4) and ethane (C2H6) taken aboard a NOAA DHC-6 Twin Otter research aircraft in May 2014 over the Williston Basin in northwestern North Dakota, a region of rapidly growing oil and natural gas production. The Williston Basin is best known for the Bakken shale formation, from which a significant increase in oil and gas extraction has occurred since 2009. We derive a CH4 emission rate from this region using airborne data by calculating the CH4 enhancement flux through the planetary boundary layer downwind of the region. We calculate CH4 emissions of (36 ± 13), (27 ± 13), (27 ± 12), (27 ± 12), and (25 ± 10) × 103 kg/h from five transects on 3 days in May 2014 downwind of the Bakken shale region of North Dakota. The average emission, (28 ± 5) × 103 kg/h, extrapolates to 0.25 ± 0.05 Tg/yr, which is significantly lower than a previous estimate of CH4 emissions from northwestern North Dakota and southeastern Saskatchewan using satellite remote sensing data. We attribute the majority of CH4 emissions in the region to oil and gas operations in the Bakken based on the similarity between atmospheric C2H6 to CH4 enhancement ratios and the composition of raw natural gas withdrawn from the region.

We present a 13 year (2002–2015) semimonthly time series of the partial pressure of CO2 in surface water (pCO2surf) and other carbonate system parameters from the Drake Passage. This record shows a clear increase in the magnitude of the sea-air pCO2 gradient, indicating strengthening of the CO2 sink in agreement with recent large-scale analyses of the world oceans. The rate of increase in pCO2surf north of the Antarctic Polar Front (APF) is similar to the atmospheric pCO2 (pCO2atm) trend, whereas the pCO2surf increase south of the APF is slower than the pCO2atm trend. The high-frequency surface observations indicate that an absence of a winter increase in total CO2 (TCO2) and cooling summer sea surface temperatures are largely responsible for increasing CO2 uptake south of the APF. Muted winter trends in surface TCO2 also provide temporary stability to the carbonate system that is already close to undersaturation with respect to aragonite.

Seasonal spatial and temporal gradients for the CO2 mole fraction over North America are examined by creating a climatology from data collected 2004–2013 by the NOAA/ESRL Global Greenhouse Gas Reference Network Aircraft Program relative to trends observed for CO2 at the Mauna Loa Observatory. The data analyzed are from measurements of air samples collected in specially fabricated flask packages at frequencies of days to months at 22 sites over continental North America and shipped back to Boulder, Colorado, for analysis. These measurements are calibrated relative to the CO2 World Meteorological Organization mole fraction scale. The climatologies of CO2 are compared to climatologies of CO, CH4, SF6, N2O (which are also measured from this sampling program), and winds to understand the dominant transport and chemical and biological processes driving changes in the spatial and temporal mole fractions of CO2 as air passes over continental North America. The measurements show that air masses coming off the Pacific on the west coast of North America are relatively homogeneous with altitude. As air masses flow eastward, the lower section from the surface to 4000 m above sea level (masl) becomes distinctly different from the 4000–8000 masl section of the column. This is due in part to the extent of the planetary boundary layer, which is directly impacted by continental sources and sinks, and to the vertical gradient in west-to-east wind speeds. The slowdown and southerly shift in winds at most sites during summer months amplify the summertime drawdown relative to what might be expected from local fluxes. This influence counteracts the dilution of summer time CO2 drawdown (known as the “rectifier effect”) as well as changes the surface influence “footprint” for each site. An early start to the summertime drawdown, a pronounced seasonal cycle in the column mean (500 to 8000 masl), and small vertical gradients in CO2, CO, CH4, SF6, and N2O at high-latitude western sites such as Poker Flat, Alaska, suggest recent influence of transport from southern latitudes and not local processes. This transport pathway provides a significant contribution to the large seasonal cycle observed in the high latitudes at all altitudes sampled. A sampling analysis of the NOAA/ESRL CarbonTracker model suggests that the average sampling resolution of 22 days is sufficient to get a robust estimate of mean seasonal cycle of CO2 during this 10 year period but insufficient to detect interannual variability in emissions over North America.

The Indianapolis Flux Experiment (INFLUX) aims to develop and assess methods for quantifying urban greenhouse gas emissions. Here we use CO2, 14CO2, and CO measurements from tall towers around Indianapolis, USA, to determine urban total CO2, the fossil fuel derived CO2 component (CO2ff), and CO enhancements relative to background measurements. When a local background directly upwind of the urban area is used, the wintertime total CO2 enhancement over Indianapolis can be entirely explained by urban CO2ff emissions. Conversely, when a continental background is used, CO2ff enhancements are larger and account for only half the total CO2 enhancement, effectively representing the combined CO2ff enhancement from Indianapolis and the wider region. In summer, we find that diurnal variability in both background CO2 mole fraction and covarying vertical mixing makes it difficult to use a simple upwind-downwind difference for a reliable determination of total CO2 urban enhancement. We use characteristic CO2ff source sector CO:CO2ff emission ratios to examine the contribution of the CO2ff source sectors to total CO2ff emissions. This method is strongly sensitive to the mobile sector, which produces most CO. We show that the inventory-based emission product (“bottom up”) and atmospheric observations (“top down”) can be directly compared throughout the diurnal cycle using this ratio method. For Indianapolis, the top-down observations are consistent with the bottom-up Hestia data product emission sector patterns for most of the diurnal cycle but disagree during the nighttime hours. Further examination of both the top-down and bottom-up assumptions is needed to assess the exact cause of the discrepancy.

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.

Emissions of methane (CH4) from oil and natural gas (O&G) operations in the most densely drilled area of the Denver-Julesburg Basin in Weld County located in northeastern Colorado are estimated for 2 days in May 2012 using aircraft-based CH4 observations and planetary boundary layer height and ground-based wind profile measurements. Total top-down CH4 emission estimates are 25.8 ± 8.4 and 26.2 ± 10.7 t CH4/h for the 29 and 31 May flights, respectively. Using inventory data, we estimate the total emissions of CH4 from non-O&G gas-related sources at 7.1 ± 1.7 and 6.3 ± 1.0 t CH4/h for these 2 days. The difference in emissions is attributed to O&G sources in the study region, and their total emission is on average 19.3 ± 6.9 t/h, close to 3 times higher than an hourly emission estimate based on Environmental Protection Agency's Greenhouse Gas Reporting Program data for 2012. We derive top-down emissions estimates for propane, n-butane, i-pentane, n-pentane, and benzene from our total top-down CH4 emission estimate and the relative hydrocarbon abundances in aircraft-based discrete air samples. Emissions for these five nonmethane hydrocarbons alone total 25.4 ± 8.2 t/h. Assuming that these emissions are solely originating from O&G-related activities in the study region, our results show that the state inventory for total volatile organic compounds emitted by O&G activities is at least a factor of 2 too low for May 2012. Our top-down emission estimate of benzene emissions from O&G operations is 173 ± 64 kg/h, or 7 times larger than in the state inventory.

[1] Methane (CH4) emissions from natural gas production are not well quantified and have the potential to offset the climate benefits of natural gas over other fossil fuels. We use atmospheric measurements in a mass balance approach to estimate CH4 emissions of 55 ± 15 × 103 kg h−1 from a natural gas and oil production field in Uintah County, Utah, on 1 day: 3 February 2012. This emission rate corresponds to 6.2%–11.7% (1σ) of average hourly natural gas production in Uintah County in the month of February. This study demonstrates the mass balance technique as a valuable tool for estimating emissions from oil and gas production regions and illustrates the need for further atmospheric measurements to determine the representativeness of our single-day estimate and to better assess inventories of CH4 emissions.

[1] Atmospheric methane (CH4) concentration in the mid-to-upper troposphere has been retrieved using atmospheric infrared sounder (AIRS) data on NASA EOS/AQUA. By selecting the AIRS strong CH4 absorption channels near 1306 cm−1, severe CH4 depletion was mapped during a stratospheric intrusion event on 27 March 2010. The areas with depleted CH4 mixing ratio are collocated with enhanced ozone (O3) and low tropopause height. Aircraft measurements observed the depleted CH4 and enhanced O3 down to 550 hPa. An estimate of the depleted CH4 amount which resulted from stratospheric intrusion is −54 to −67 Tg yr−1. This study suggests that the AIRS and/or other thermal infrared sounders can provide an observation of CH4 variation associated with stratospheric intrusion, a key unknown in CH4 budget, and this data set will be also useful for studying the stratosphere-troposphere exchange (STE).

The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21st century. This increase will reduce the concentration of CO32− of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage. Using the large 2650 m3 coral reef mesocosm at the BIOSPHERE-2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcification of coral reef organisms at the community scale. Our experimental design was to obtain a long (3.8 years) time series of the net calcification of the complete system and all relevant physical and chemical variables (temperature, salinity, light, nutrients, Ca2+,pCO2, TCO2, and total alkalinity). Periodic additions of NaHCO3, Na2CO3, and/or CaCl2 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcification in response to our manipulations of the saturation state. We show that the net community calcification rate responds to manipulations in the concentrations of both Ca2+ and CO32− and that the rate is well described as a linear function of the ion concentration product, [Ca2+]0.69[CO32−]. This suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcification on coral reefs at the ecosystem level. We compare the sensitivity of calcification to short-term (days) and long-term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification between the years 1880 and 2065 A.D. based on our long-term results is 40%. Previous small-scale, short-term organismal studies predicted a calcification reduction of 14-30%. This much longer, community-scale study suggests that the impact on coral reefs may be greater than previously suspected. In the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses.

[1] In any data assimilation framework, the background error covariance statistics play the critical role of filtering the observed information and determining the quality of the analysis. For atmospheric CO2 data assimilation, however, the background errors cannot be prescribed via traditional forecast or ensemble-based techniques as these fail to account for the uncertainties in the carbon emissions and uptake, or for the errors associated with the CO2 transport model. We propose an approach where the differences between two modeled CO2 concentration fields, based on different but plausible CO2 flux distributions and atmospheric transport models, are used as a proxy for the statistics of the background errors. The resulting error statistics: (1) vary regionally and seasonally to better capture the uncertainty in the background CO2 field, and (2) have a positive impact on the analysis estimates by allowing observations to adjust predictions over large areas. A state-of-the-art four-dimensional variational (4D-VAR) system developed at the European Centre for Medium-Range Weather Forecasts (ECMWF) is used to illustrate the impact of the proposed approach for characterizing background error statistics on atmospheric CO2 concentration estimates. Observations from the Greenhouse gases Observing SATellite “IBUKI” (GOSAT) are assimilated into the ECMWF 4D-VAR system along with meteorological variables, using both the new error statistics and those based on a traditional forecast-based technique. Evaluation of the four-dimensional CO2 fields against independent CO2 observations confirms that the performance of the data assimilation system improves substantially in the summer, when significant variability and uncertainty in the fluxes are present.

[1] This analysis provides an up-to-date assessment of long-term (1990–2010) rural ozone trends using all available data in the western (12 sites) and eastern (41 sites) USA. Rather than focus solely on average ozone values or air quality standard violations, we consider the full range of ozone values, reporting trends for the 5th, 50th and 95th percentiles. Domestic ozone precursor emissions decreased strongly during 1990–2010. Accordingly 83%, 66% and 20% of summertime eastern U.S. sites experienced statistically significant ozone decreases in the 95th, 50th and 5th percentiles, respectively. During spring 43% of the eastern sites have statistically significant ozone decreases for the 95th percentile with no sites showing a significant increase. At the 50th percentile there is little overall change in the eastern U.S. In contrast, only 17% (2 sites) and 8% (1 site) of summertime western U.S. sites have statistically significant ozone decreases in the 95th and 50th percentiles, respectively. During spring no western site has a significant decrease, while 50% have a significant median increase. This dichotomy in U.S. ozone trends is discussed in terms of changing anthropogenic and biomass burning emissions. Consideration is given to the concept that increasing baseline ozone flowing into the western U.S. is counteracting ozone reductions due to domestic emission reductions. An update to the springtime free tropospheric ozone trend above western North America shows that ozone has increased significantly from 1995 to 2011 at the rate of 0.41 ± 0.27 ppbv yr−1. Finally, the ozone changes are examined in relation to regional temperature trends.

[1] We estimate nitrous oxide (N2O) emissions from Central California for the period of December 2007 through November 2009 by comparing N2O mixing ratios measured at a tall tower (Walnut Grove, WGC) with transport model predictions based on two global a priori N2O emission models (EDGAR32 and EDGAR42). Atmospheric particle trajectories and surface footprints are computed using the Weather Research and Forecasting (WRF) and Stochastic Time-Inverted Lagrangian Transport (STILT) models. Regression analyses show that the slopes of predicted on measured N2O from both emission models are low, suggesting that actual N2O emissions are significantly higher than the EDGAR inventories for all seasons. Bayesian inverse analyses of regional N2O emissions show that posterior annual N2O emissions are larger than both EDGAR inventories by factors of 2.0 ± 0.4 (EDGAR32) and 2.1 ± 0.4 (EDGAR42) with seasonal variation ranging from 1.6 ± 0.3 to 2.5 ± 0.4 for an influence region of Central California within approximately 150 km of the tower. These results suggest that if the spatial distribution of N2O emissions in California follows the EDGAR emission models, then actual emissions are 2.7 ± 0.5 times greater than the current California emission inventory, and total N2O emissions account for 8.1 ± 1.4% of total greenhouse gas emissions from California.

[1] Atmospheric CO2 gradients are usually dominated by the signal from net terrestrial biological fluxes, despite the fact that fossil fuel combustion fluxes are larger in the annual mean. Here, we use a six year long series of 14CO2 and CO2 measurements obtained from vertical profiles at two northeast U.S. aircraft sampling sites to partition lower troposphere CO2 enhancements (and depletions) into terrestrial biological and fossil fuel components (Cbio and Cff). Mean Cff is 1.5 ppm, and 2.4 ppm when we consider only planetary boundary layer samples. However, we find that the contribution of Cbio to CO2 enhancements is large throughout the year, and averages 60% in winter. Paired observations of Cff and the lower troposphere enhancements (Δgas) of 22 other anthropogenic gases (CH4, CO, halo- and hydrocarbons and others) measured in the same samples are used to determine apparent emission ratios for each gas. We then scale these ratios by the well known U.S. fossil fuel CO2 emissions to provide observationally based estimates of national emissions for each gas and compare these to “bottom up” estimates from inventories. Correlations of Δgas with Cff for almost all gases are statistically significant with median r2for winter, summer and the entire year of 0.59, 0.45, and 0.42, respectively. Many gases exhibit statistically significant winter:summer differences in ratios that indicate seasonality of emissions or chemical destruction. The variability of ratios in a given season is not readily attributable to meteorological or geographic variables and instead most likely reflects real, short-term spatiotemporal variability of emissions.

[1] The multispecies analysis of daily air samples collected at the NOAA Boulder Atmospheric Observatory (BAO) in Weld County in northeastern Colorado since 2007 shows highly correlated alkane enhancements caused by a regionally distributed mix of sources in the Denver-Julesburg Basin. To further characterize the emissions of methane and non-methane hydrocarbons (propane, n-butane, i-pentane, n-pentane and benzene) around BAO, a pilot study involving automobile-based surveys was carried out during the summer of 2008. A mix of venting emissions (leaks) of raw natural gas and flashing emissions from condensate storage tanks can explain the alkane ratios we observe in air masses impacted by oil and gas operations in northeastern Colorado. Using the WRAP Phase III inventory of total volatile organic compound (VOC) emissions from oil and gas exploration, production and processing, together with flashing and venting emission speciation profiles provided by State agencies or the oil and gas industry, we derive a range of bottom-up speciated emissions for Weld County in 2008. We use the observed ambient molar ratios and flashing and venting emissions data to calculate top-down scenarios for the amount of natural gas leaked to the atmosphere and the associated methane and non-methane emissions. Our analysis suggests that the emissions of the species we measured are most likely underestimated in current inventories and that the uncertainties attached to these estimates can be as high as a factor of two.

[1] CO2 surface fluxes that are statistically consistent with surface layer measurements of CO2, when propagated forward in time by atmospheric transport models, underestimate the seasonal cycle amplitude of total column CO2 in the northern temperate latitudes by 1–2 ppm. In this paper we verify the systematic nature of this underestimation at a number of Total Carbon Column Observation Network (TCCON) stations by comparing their measurements with a number of transport models. In particular, at Park Falls, Wisconsin (United States), we estimate this mismatch to be 1.4 ppm and try to attribute portions of this mismatch to different factors affecting the total column. We find that errors due to (1) the averaging kernel and prior profile used in forward models, (2) water vapor in the model atmosphere, (3) incorrect vertical transport by transport models in the free troposphere, (4) incorrect aging of air in transport models in the stratosphere, and (5) air mass dependence in TCCON data can explain up to 1 ppm of this mismatch. The remaining 0.4 ppm mismatch is at the edge of the ≤0.4 ppm accuracy requirement on satellite measurements to improve on our current estimate of surface fluxes. Uncertainties in the biosphere fluxes driving the transport models could explain a part of the remaining 0.4 ppm mismatch, implying that with corrections to the factors behind the accounted-for 1 ppm underestimation, present inverse modeling frameworks could effectively assimilate satellite CO2 measurements.

[1] Measurements of atmospheric N2O spanning altitudes from the surface to 14 km, and latitudes from 67°S to 85°N, show high concentrations in the tropics and subtropics, with strong maxima in the middle and upper troposphere. The pattern varies significantly over time scales of a few weeks. Global simulations do not accurately capture observed distributions with latitude, altitude, or time. Inversion results indicate strong, episodic inputs of nitrous oxide from tropical regions (as large as 1 Tg N-N2O over 9 weeks) are necessary to produce observed vertical and latitudinal distributions. These findings highlight strong tropical sources of N2O with high temporal variability, and the necessity of using full vertical profile observations in deriving emissions from atmospheric measurements.

[1] Spaceborne measurements by the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua satellite provide a global view of the methane (CH4) distribution in the mid-upper troposphere (MUT-CH4). The focus of this study is to examine the spatiotemporal variation of MUT-CH4 in the high Northern Hemisphere (HNH) using AIRS retrievals, aircraft measurements, and simulations from a forward chemistry-transport model (i.e., ACTM). Data from 2004 and 2005 focusing over two regions (Alaska and Siberia) are analyzed. An important feature in the seasonal variation of CH4 we found is the summer increase of MUT-CH4, which is nearly opposite to the summer minimum of CH4 in the marine boundary layer (MBL). This study also demonstrated an apparent increase of CH4 over Alaska associated with the 2004 Alaska forest fire and a negative bias of the ACTM simulations in the HNH. The larger bias of the model simulations in the late winter to early spring may indicate possible unidentified CH4 emission sources (e.g., the use of energy or gas leakage) during this period, but more studies will be needed due to the retrieval uncertainties in the polar winter season. The summer increase of MUT-CH4 is related to surface emission, but the enhanced convection in summer is likely the most important driver.

[1] Antarctic coastal waters have an abundance of marine organisms that secrete the mineral aragonite for growth and survival. Increasing oceanic anthropogenic CO2 uptake will push these waters to a point whereby aragonite will start to geochemically corrode, with direct consequences for the Antarctic ecosystem. Here we combine surface CO2 data in the Ross Sea, Antarctica with a regional ocean/sea-ice model to better pinpoint the timing of corrosive conditions. Our analysis suggests sea-ice cover and deep-water entrainment during winter results in 65% lower storage of anthropogenic CO2 in comparison to atmospheric CO2 equilibrium. This means that instead of corrosive ‘acidified’ waters beginning as early as the winter of 2015, anthropogenic CO2 disequilibrium delays its onset by up to 30 years, giving this Antarctic marine ecosystem a several decade reprieve to corrosive conditions. Our results demonstrate a broader importance of understanding natural oceanic carbon cycle variability for the onset of corrosive conditions.

[1] The Southern Ocean is a climatically sensitive region that plays an important role in the regional and global modulation of atmospheric CO2. Based on satellite-derived sea ice data, wind and cloudiness estimates from numerical models (National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis), and in situ measurements of surface (0–20 m depth) chlorophyll a (ChlSurf) and dissolved inorganic carbon (DICSurf) concentration, we show sea ice concentration from June to November and spring wind patterns between 1979 and 2006 had a significant influence on midsummer (January) primary productivity and carbonate chemistry for the Western Shelf of the Antarctic Peninsula (WAP, 64°–68°S, 63.4°–73.3°W). In general, strong (>3.5 m s−1) and persistent (>2 months) northerly winds during the previous spring were associated with relatively high (monthly mean > 2 mg m−3) ChlSurf and low (monthly mean 200 m depth) “winter-like” DIC on the WAP.

[1] This paper presents the characterization and validation of retrievals of atmospheric methane (CH4) vertical profiles by the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua platform. AIRS channels near 7.6 μm are used for CH4 retrieval, and they are most sensitive to the middle to upper troposphere, i.e., about 200–300 hPa in the tropics and 400–500 hPa in the polar region. The atmospheric temperature-humidity profiles, surface skin temperature, and emissivity required to derive CH4 are obtained from retrievals using separate AIRS channels and the Advanced Microwave Sounding Unit (AMSU). Comparison of AIRS retrieved profiles with some in situ aircraft CH4 profiles implied that the forward model used in the AIRS retrieval system V4.0 required a 2% increase in methane absorption coefficients for strong absorption channels, and this bias adjustment was implemented in the AIRS retrieval system V5.0. As a new operational product in V5.0, AIRS CH4 were validated using in situ aircraft observations at 22 sites of the NOAA Earth System Research Laboratory, Global Monitoring Division (NOAA/ESRL/GMD), ranging from the Arctic to the tropical South Pacific Ocean, but their altitudes are usually above 300 hPa. The results show the bias of the retrieved CH4 profiles for this version is −1.4∼0.1% and its RMS difference is about 0.5–1.6%, depending on altitude. These validation comparisons provide critical assessment of the retrieval algorithm and will continue using more in situ observations together with future improvement to the retrieval algorithm. AIRS CH4 products include not only the CH4 profile but also the information content. As examples, the products of AIRS CH4 in August 2004 and the difference of CH4 in May and September 2004 are shown. From these results a few features are evident: (1) a large AIRS CH4 plume southwest of the Tibetan plateau that may be associated with deep convection during the Asian summer monsoon; (2) high mixing ratios of AIRS CH4 in southeastern Asia and in the high northern hemisphere in the summer; and (3) the increase of AIRS CH4 from May to September in the high northern hemisphere that is likely linked with wetland emission but needs more study. Further analysis of these data and its comparison with model data will be addressed in a separate paper.

In this paper we describe the methodology of an offline retrieval of CO 2 from AIRS data and show comparisons of these retrievals with all available NOAA ESRL/GMD aircraft data during 2005. In general, we find that when compared to the aircraft the AIRS CO 2 estimates agree to approximately ±0.5% in middle-tropospheric CO 2 column abundances between ±65 degrees latitude.

[1] The 14CO2 released into the stratosphere during bomb testing in the early 1960s provides a global constraint on air-sea gas exchange of soluble atmospheric gases like CO2. Using the most complete database of dissolved inorganic radiocarbon, DI14C, available to date and a suite of ocean general circulation models in an inverse mode we recalculate the ocean inventory of bomb-produced DI14C in the global ocean and confirm that there is a 25% decrease from previous estimates using older DI14C data sets. Additionally, we find a 33% lower globally averaged gas transfer velocity for CO2 compared to previous estimates (Wanninkhof, 1992) using the NCEP/NCAR Reanalysis 1 1954–2000 where the global mean winds are 6.9 m s−1. Unlike some earlier ocean radiocarbon studies, the implied gas transfer velocity finally closes the gap between small-scale deliberate tracer studies and global-scale estimates. Additionally, the total inventory of bomb-produced radiocarbon in the ocean is now in agreement with global budgets based on radiocarbon measurements made in the stratosphere and troposphere. Using the implied relationship between wind speed and gas transfer velocity ks = 0.27〈u102〉(Sc/660)−0.5 and standard partial pressure difference climatology of CO2 we obtain an net air-sea flux estimate of 1.3 ± 0.5 PgCyr−1 for 1995. After accounting for the carbon transferred from rivers to the deep ocean, our estimate of oceanic uptake (1.8 ± 0.5 PgCyr−1) compares well with estimates based on ocean inventories, ocean transport inversions using ocean concentration data, and model simulations.

[1] Measurements of carbonyl sulfide (COS) from a global air-monitoring network over multiple years suggest that atmospheric mixing ratios of COS are strongly influenced by terrestrial vegetation in the Northern Hemisphere (NH) and by the oceans in the Southern Hemisphere (SH). The annual mean NH mixing ratio estimated from results at seven surface sites during 2000.2–2005.2 was 476 ± 4 ppt, or slightly less than the mean of 491 ± 2 ppt derived from results at three surface sites in the SH. The lowest annual mean mixing ratios were measured at low-altitude continental sites in the midlatitude and high-latitude NH. Mixing ratios undergo substantial seasonal variations at nearly all sites across the globe; the largest seasonal variations are observed at the NH sites having the lowest annual means. There is little coherence in the seasonality in the NH and SH, suggesting that the COS seasonality is driven by different processes in each hemisphere. These seasonal changes cause the NH/SH ratio, as estimated from the available surface data, to vary regularly from 0.91 ± 0.01 to 1.04 ± 0.02 across a year; the annual mean NH/SH ratio was 0.97 ± 0.01. Results from over 160 aircraft profiles regularly collected at eight sites over the continental United States throughout an entire year reveal substantial vertical gradients for COS mixing ratios that vary with season. While similar mixing ratios are observed throughout the NH troposphere during January–April (up to 8 km above sea level (asl)), during the growing season substantially reduced mixing ratios are observed in the boundary layer above the continental United States (defined here as

[1] Observations of SF6 are used to quantify the mean time since air was in (“mean age” from) the Northern Hemisphere (NH) midlatitude surface layer. The mean age is a fundamental property of tropospheric transport that can be used in theoretical studies and used to evaluate transport in comprehensive models. Comparisons of simulated SF6 and an idealized clock tracer confirm that the time lag between the SF6 mixing ratio at a given location and the NH midlatitude surface provides an accurate estimate of the mean age. The ages calculated from surface SF6 measurements show large meridional gradients in the tropics but weak gradients in the extratropics, with near-zero ages at the surface north of 30°N and ages around 1.4 years south of 30°S. Aircraft measurements show weak vertical age gradients in the lower and middle troposphere, with only slight increases of age with height in the NH and slight decreases with height in the Southern Hemisphere. There are large seasonal variations in the age at tropical stations (annual amplitudes around 0.5–1.0 year), with younger ages during northern winter, but only weak seasonal variations at higher latitudes. The seasonality and interannual variations in the tropics and Southern Hemisphere are related to changes in locations of tropical convection. There is qualitative agreement, in both spatial and temporal variations, between the simulated ages and observations. The model ages tend to be older than observed, with differences of ~0.2 year in the Northern Hemisphere upper troposphere and throughout the Southern Hemisphere troposphere.

[1] The tropospheric seasonal cycles of N2O, CFC-11 (CCl3F), and CFC-12 (CCl2F2) are influenced by atmospheric dynamics. The interannually varying summertime minima in mole fractions of these trace gases have been attributed to interannual variations in mixing of stratospheric air (depleted in CFCs and N2O) with tropospheric air with a few months lag. The amount of wave activity that drives the stratospheric circulation and influences the winter stratospheric jet and subsequent mass transport across the tropopause appears to be the primary cause of this interannual variability. We relate the observed seasonal minima of species at three Northern Hemisphere sites (Mace Head, Ireland; Trinidad Head, U.S.; and Barrow, Alaska) with the behavior of the winter stratospheric jet. As a result, a good correlation is obtained between zonal winds in winter at 10 hPa, 58°N–68°N, and the detrended seasonal minima in the stratosphere-influenced tracers. For these three tracers, individual Pearson correlation coefficients (r) between 0.51 and 0.71 were found, with overall correlations of between 0.67 and 0.77 when “composite species” were considered. Finally, we note that the long-term observations of CFCs and N2O in the troposphere provide an independent monitoring method complementary to satellite data. Furthermore, they could provide a useful observational measure of the strength of stratosphere-troposphere exchange and, thus, could be used to monitor any long-term trend in the Brewer-Dobson circulation which is predicted by climate models to increase over the coming decades.