Search for: All records

We present improved estimates of air–sea CO₂exchange over three latitude bands of the Southern Ocean using atmospheric CO₂measurements from global airborne campaigns and an atmospheric 4-box inverse model based on a mass-indexed isentropic coordinate (M_θe). These flux estimates show two features not clearly resolved in previous estimates based on inverting surface CO₂measurements: a weak winter-time outgassing in the polar region and a sharp phase transition of the seasonal flux cycles between polar/subpolar and subtropical regions. The estimates suggest much stronger summer-time uptake in the polar/subpolar regions than estimates derived through neural-network interpolation of pCO₂data obtained with profiling floats but somewhat weaker uptake than a recent study by Long et al. [Science374, 1275–1280 (2021)], who used the same airborne data and multiple atmospheric transport models (ATMs) to constrain surface fluxes. Our study also uses moist static energy (MSE) budgets from reanalyses to show that most ATMs tend to have excessive diabatic mixing (transport across moist isentrope, θ_e, or M_θesurfaces) at high southern latitudes in the austral summer, which leads to biases in estimates of air–sea CO₂exchange. Furthermore, we show that the MSE-based constraint is consistent with an independent constraint on atmospheric mixing based on combining airborne and surface CO₂observations.

 

As the majority of fossil fuel carbon dioxide (CO₂) emissions originate from cities, the use of novel techniques to leverage available satellite observations of CO₂and proxy species to constrain urban CO₂is of great importance. In this study, we seek to empirically determine relationships between satellite observations of CO₂and the proxy species nitrogen dioxide (NO₂), applying these relationships to NO₂fields to generate NO₂‐derived CO₂fields (NDCFs) from which CO₂emissions can be estimated. We first establish this method using simulations of CO₂and NO₂for the cities of Buenos Aires, Melbourne, and Mexico City, finding that the method is viable throughout the year. For the same three cities, we next calculate empirical relationships (slopes) between co‐located observations of NO₂from the Tropospheric Monitoring Instrument and Snapshot Area Mode observations of CO₂from Orbiting Carbon Observatory‐3. Applying varying combinations of slopes to generate NDCFs, we evaluate methodological uncertainties for each slope application method and use a simple mass balance method to estimate CO₂emissions from NDCFs. We demonstrate monthly urban CO₂emissions estimates that are comparable to emissions inventory estimates. We additionally prove the utility of our method by demonstrating how large uncertainties at a grid cell level (equivalent to ∼1–3 ppm) can be reduced substantially when aggregating emissions estimates from NDCFs generated from all NO₂swaths (about 1%–6%). Rather than rely on prior knowledge of emission ratios, our method circumvents such assumptions and provides a valuable observational constraint on urban CO₂emissions.

 

The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO 2 ), yet estimates of air-sea CO 2 flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO 2 exchange by relating fluxes to horizontal and vertical CO 2 gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO 2 gradient provide robust flux constraints. We found an annual mean flux of –0.53 ± 0.23 petagrams of carbon per year (net uptake) south of 45°S during the period 2009–2018. This is consistent with the mean of atmospheric inversion estimates and surface-ocean partial pressure of CO 2 ( P co 2 )–based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations. 

Abstract. We apply airborne measurements across three seasons(summer, winter and spring 2017–2018) in a multi-inversion framework toquantify methane emissions from the US Corn Belt and Upper Midwest, a keyagricultural and wetland source region. Combing our seasonal results withprior fall values we find that wetlands are the largest regional methanesource (32 %, 20 [16–23] Gg/d), while livestock (enteric/manure; 25 %,15 [14–17] Gg/d) are the largest anthropogenic source. Naturalgas/petroleum, waste/landfills, and coal mines collectively make up theremainder. Optimized fluxes improve model agreement with independentdatasets within and beyond the study timeframe. Inversions reveal coherentand seasonally dependent spatial errors in the WetCHARTs ensemble meanwetland emissions, with an underestimate for the Prairie Pothole region butan overestimate for Great Lakes coastal wetlands. Wetland extent andemission temperature dependence have the largest influence on predictionaccuracy; better representation of coupled soil temperature–hydrologyeffects is therefore needed. Our optimized regional livestock emissionsagree well with the Gridded EPA estimates during spring (to within 7 %) butare ∼ 25 % higher during summer and winter. Spatial analysisfurther shows good top-down and bottom-up agreement for beef facilities (withmainly enteric emissions) but larger (∼ 30 %) seasonaldiscrepancies for dairies and hog farms (with > 40 % manureemissions). Findings thus support bottom-up enteric emission estimates butsuggest errors for manure; we propose that the latter reflects inadequatetreatment of management factors including field application. Overall, ourresults confirm the importance of intensive animal agriculture for regionalmethane emissions, implying substantial mitigation opportunities throughimproved management. 

Abstract. We present the development and assessment of a new flight system that uses acommercially available continuous-wave, tunable infrared laser directabsorption spectrometer to measure N₂O, CO₂, CO, andH₂O. When the commercial system is operated in an off-the-shelfmanner, we find a clear cabin pressure–altitude dependency forN₂O, CO₂, and CO. The characteristics of this artifactmake it difficult to reconcile with conventional calibration methods. Wepresent a novel procedure that extends upon traditional calibrationapproaches in a high-flow system with high-frequency, short-duration samplingof a known calibration gas of near-ambient concentration. This approachcorrects for cabin pressure dependency as well as other sources of drift inthe analyzer while maintaining a ∼90% duty cycle for 1Hz sampling.Assessment and validation of the flight system with both extensive in-flightcalibrations and comparisons with other flight-proven sensors demonstrate thevalidity of this method. In-flight 1σ precision is estimated at0.05ppb, 0.10ppm, 1.00ppb, and 10ppm for N₂O,CO₂, CO, and H₂O respectively, and traceability to WorldMeteorological Organization (WMO) standards (1σ) is 0.28ppb,0.33ppm, and 1.92ppb for N₂O, CO₂, and CO. We showthe system is capable of precise, accurate 1Hz airborne observations ofN₂O, CO₂, CO, and H₂O and highlight flightdata, illustrating the value of this analyzer for studying N₂Oemissions on ∼100km spatial scales.

 

We use TROPOMI (TROPOspheric Monitoring Instrument) tropospheric nitrogen dioxide (NO₂) measurements to identify cropland soil nitrogen oxide (NO_x = NO + NO₂) emissions at daily to seasonal scales in the U.S. Southern Mississippi River Valley. Evaluating 1.5 years of TROPOMI observations with a box model, we observe seasonality in local NO_xenhancements and estimate maximum cropland soil NO_xemissions (15–34 ng N m⁻² s⁻¹) early in growing season (May–June). We observe soil NO_xpulsing in response to daily decreases in volumetric soil moisture (VSM) as measured by the Soil Moisture Active Passive (SMAP) satellite. Daily NO₂enhancements reach up to 0.8 × 10¹⁵ molecules cm⁻²4–8 days after precipitation when VSM decreases to ~30%, reflecting emissions behavior distinct from previously defined soil NO_xpulse events. This demonstrates that TROPOMI NO₂observations, combined with observations of underlying process controls (e.g., soil moisture), can constrain soil NO_xprocesses from space.

 

We present airborne observations of the vertical gradient of atmospheric oxygen (δ(O₂/N₂)) and carbon dioxide (CO₂) through the atmospheric boundary layer (BL) over the Drake Passage region of the Southern Ocean, during the O₂/N₂Ratio and CO₂Airborne Southern Ocean Study, from 15 January to 29 February 2016. Gradients were predominately anticorrelated, with excesses ofδ(O₂/N₂) and depletions of CO₂found within the boundary layer, relative to a mean reference height of 1.7 km. Through analysis of the molar ratio of the gradients (GR), the behavior of other trace gases measured in situ, and modeling experiments with the Community Earth System Model, we found that the main driver of gradients was air‐sea exchange of O₂and CO₂driven by biological processes, more so than solubility effects. An exception to this was in the eastern Drake Passage, where positive GRs were occasionally observed, likely due to the dominance of thermal forcing on the air‐sea flux of both species. GRs were more spatially consistent than the magnitudes of the gradients, suggesting that GRs can provide integrated process constraints over broad spatial scales. Based on the model simulation within a domain bounded by 45°S, 75°S, 100°W, and 45°W, we show that the sampling density of the campaign was such that the observed mean GR (± standard error), −4.0± 0.8 mol O₂per mol CO₂, was a reasonable proxy for both the mean GR and the mean molar ratio of air‐sea fluxes of O₂and CO₂during the O₂/N₂Ratio and CO₂Airborne Southern Ocean Study.

 

Carbon monoxide (CO) is an ozone precursor, oxidant sink, and widely used pollution tracer. The importance of anthropogenic versus other CO sources in the US is uncertain. Here, we interpret extensive airborne measurements with an atmospheric model to constrain US fossil and nonfossil CO sources. Measurements reveal a low bias in the simulated CO background and a 30% overestimate of US fossil CO emissions in the 2016 National Emissions Inventory. After optimization we apply the model for source partitioning. During summer, regional fossil sources account for just 9%–16% of the sampled boundary layer CO, and 32%–38% of the North American enhancement—complicating use of CO as a fossil fuel tracer. The remainder predominantly reflects biogenic hydrocarbon oxidation plus fires. Fossil sources account for less domain‐wide spatial variability at this time than nonfossil and background contributions. The regional fossil contribution rises in other seasons, and drives ambient variability downwind of urban areas.