Attributing observed CO 2 variations to human or natural cause is critical to deducing and tracki... more Attributing observed CO 2 variations to human or natural cause is critical to deducing and tracking emissions from observations. We have used in situ CO 2 , CO, and planetary boundary layer height (PBLH) measurements recorded during the CalNex-LA (CARB et al., 2008) ground campaign of 15 May-15 June 2010, in Pasadena, CA, to deduce the diurnally varying anthropogenic component of observed CO 2 in the megacity of Los Angeles (LA). This affordable and simple technique, validated by carbon isotope observations, is shown to robustly attribute observed CO 2 variation to anthropogenic or biogenic origin. During CalNex-LA, local fossil fuel combustion contributed up to ∼50 % of the observed CO 2 enhancement overnight, and ∼100 % during midday. This suggests midday column observations over LA, such as those made by satellites relying on reflected sunlight, can be used to track anthropogenic emissions.
Representations of the changing global carbon cycle under climatic and environmental perturbation... more Representations of the changing global carbon cycle under climatic and environmental perturbations require highly detailed accounting of all atmosphere and biosphere exchange. These fluxes remain unsatisfactory, as a consequence of only having data with limited spatiotemporal coverage and precision, which restrict accurate assessments. Through the nature of intimate coupling of global carbon and oxygen cycles via O 2 and CO 2 and their unique triple oxygen isotope compositions in the biosphere and atmosphere, greater insight is available. We report analysis of their isotopic compositions with the widest geographical and temporal coverage (123 new measurements for CO 2 ) and constrain, on an annual basis, the global CO 2 recycling time (1.5 ± 0.2 year) and gross primary productivities of terrestrial (~ 170-200 PgC/year) and oceanic (~ 90-120 PgC/year) biospheres. Observed inter-annual variations in CO 2 triple oxygen isotopic compositions were observed at a magnitude close to the largest contrast set by the terrestrial and oceanic biospheres. The seasonal cycles between the east and west Pacific Ocean were found to be drastically different. This intraannual variability implies that the entire atmospheric CO 2 turnover time is not much longer than the tropospheric mixing time (less than ~ 5 months), verifying the derived recycling time. The new measurements, analyses, and incorporation of other global data sets allow development of an independent approach, providing a strong constraint to biogeochemical models. Imbalance between CO 2 sources and sinks results in increasing atmospheric CO 2 levels 1-3 . The increase is due mainly to fossil fuel burning, emitting at an average rate of 9.4 ± 0.5 PgC/year 2 . As a consequence, the average global temperature has increased by 1.1 °C3 . The combined effect of elevated atmospheric CO 2 levels and temperature leads to observable changes in the global carbon cycle . A number of efforts have been used to quantify the changes of the carbon cycles in response to changing environments . Climate models coupled with biogeochemical modules are frequently used to assess changing ecosystems in the context of changing climate . However, it has been noted that current knowledge is insufficient to simulate and project the ecosystem responses 6,7 , owing to the boundaries of our knowledge of the gross processes. Reviewing the input components and processes considered , terrestrial net ecosystem exchange (NEE) is better studied but gross primary production (GPP) processes (such as photosynthesis) comprising > 3/4 of the total carbon fluxes in the carbon cycling budget remain least well-constrained 8,10-18 . The incomplete knowledge of the gross processes is largely due to rapid hydration and dehydration of CO 2 occurring in chloroplasts; it is also because of this fast reaction that regional and global assessments of the gross components are possible . The carbonic anhydrase
The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution ... more The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution spectra of reflected sunlight in three near-infrared bands centered around 0.76, 1.6, and 2.3 µm and to deliver simultaneous retrievals of column-averaged dry air mole fractions of CO 2 , CH 4 , CO, and H 2 O (denoted XCO 2 , XCH 4 , XCO, and XH 2 O, respectively) at different times of day over North America. In this study, we perform radiative transfer simulations over both clear-sky and all-sky scenes expected to be observed by GeoFTS and estimate the prospective performance of retrievals based on results from Bayesian error analysis and characterization. We find that, for simulated clear-sky retrievals, the average retrieval biases and single-measurement precisions are < 0.2 % for XCO 2 , XCH 4 , and XH 2 O, and < 2 % for XCO, when the a priori values have a bias of 3 % and an uncertainty of 3 %. In addition, an increase in the amount of aerosols and ice clouds leads to a notable increase in the retrieval biases and slight worsening of the retrieval precisions. Furthermore, retrieval precision is a strong function of signal-to-noise ratio and spectral resolution. This simulation study can help guide decisions on the design of the GeoFTS observing system, which can result in cost-effective measurement strategies while achieving satisfactory levels of retrieval precisions and biases. The simultaneous retrievals at different times of day will be important for more accurate estimation of carbon sources and sinks on fine spatiotemporal scales and for studies related to the atmospheric component of the water cycle.
Beryllium-7 ( 7 Be), produced by the interaction of cosmic radiation with atoms and molecules pri... more Beryllium-7 ( 7 Be), produced by the interaction of cosmic radiation with atoms and molecules primarily in the upper troposphere and lower stratosphere, provides a useful tracer of cross-tropopause transport and vertical mixing in the troposphere. In the western Pacific subtropical region, the interaction of the subtropical jet stream with monsoon systems potentially enhances the transport. Here, we report one year of 7 Be measurements at daily resolution during 2010, at Mt. Lulin (2862 m above mean sea level; NOAA code: LLN), along with other gaseous compounds such as O 3 and CO and meteorological information, to assess processes that affect the variability of 7 Be. The 7 Be concentrations are of the order 1 mBq/m 3 or less. The 7 Be activity is generally low during summer, largely due to precipitation and unfavorable conditions of atmospheric dynamics (i.e., prevalence of upward motion), but it is occasionally high because of the influence of typhoons. In winter and spring, stratospheric effects observed at the surface were frequent and significant, thereby directly affecting the strength of stratospheric effects on the troposphere, such as the tropospheric oxidation capacity. The effects of the stratospheric intrusions are seen by negative and positive correlations of 7 Be with relative humidity and concentration of O 3 , respectively. The stratospheric effect is further supported by the presence of downwelling transport in this region in the European Centre for Medium-Range Weather Forecasts-Atmospheric Composition Reanalysis Version 4 CO, O 3 , and relative humidity data.
Eleven glasses recovered from Holes 786A and 786B were fresh enough for volatile analysis by infr... more Eleven glasses recovered from Holes 786A and 786B were fresh enough for volatile analysis by infrared spectroscopy. The compositions of these glasses range from boninitic to rhyolitic. The glasses from the boninites contain 1.4 to 1.7 wt% H 2 O, while the rhyolitic glasses contain 2 to 6 wt% H 2 O, and all glasses have less than 30 to 40 ppm CO 2 . The highest H 2 O contents are probably the result of seawater alteration. The unaltered dacitic to rhyolitic glasses were probably quenched at low pressures corresponding to depths of 0-700 m below the seafloor, also corresponding to the depths of collection of these samples, although the water depths may have been different between the Eocene and the present. The lower boninitic H 2 O contents in vesicular glasses suggest shallow quenching on the seafloor.
Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as ... more Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as carbon dioxide (CO2) and methane (CH4) that contribute to modern-day climate change. As such, a growing number of urban policymakers and stakeholders are adopting emission reduction targets and implementing policies to reach those targets. Over the past two decades research teams have established urban GHG monitoring networks to determine how much, where, and why a particular city emits GHGs, and to track changes in emissions over time. Coordination among these efforts has been limited, restricting the scope of analyses and insights. Here we present a harmonized data set synthesizing urban GHG observations from cities with monitoring networks across North America that will facilitate cross-city analyses and address scientific questions that are difficult to address in isolation.
California has been in a severe drought for five years affec5ng weather, vegeta5on, and policy. U... more California has been in a severe drought for five years affec5ng weather, vegeta5on, and policy. Unfortunately, the last year’s strong El Nino condi5ons did not bring the expected extra rainfall relief to southern California, and we are just finishing a year of water ra5oning, concentra5ng on limi5ng irriga5on of outdoor landscape. What changes in the atmospheric CO2 composi5on in the Los Angeles, CA (LA) megacity have occurred during this period? We inves5gate changes reflected in the radiocarbon (ΔC) and stable carbon isotopic composi5on (δC) of the CO2 in LA, using the long-‐term flask sample record at our Pasadena (18 years, 11 with Δ14C; samples collected on alternate aXernoons at 14:00 PST) site (Fig. 1) to put the last five years in context. Pasadena is inland and a good receptor site for emissions in the LA basin for much of the year when the prevailing winds are from the ocean passing over LA. Radiocarbon measurements give informa5on on the fossil fuel and biosphere compone...
H.D. Graven, T. Lueker, M. Fischer, K. Brophy, T. Guilderson, R. Keeling, T. Arnold, R. Bambha, W... more H.D. Graven, T. Lueker, M. Fischer, K. Brophy, T. Guilderson, R. Keeling, T. Arnold, R. Bambha, W. Callahan, E. Campbell, C. Frankenberg, Y. Hsu, L. Iraci, S. Jeong, J. Kim, B. LaFranchi, S. Lehman, A. Manning, H. Michelson, J. Miller, S. Newman, W. Paplawsky, N. Parazoo, C. Sloop, S. Walker, M. Whelan, D. Wunch Imperial College London, Scripps Institution of Oceanography, Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, Met Office Hadley Centre, Sandia National Laboratory, Earth Networks, University of California, Merced, NASA Jet Propulsion Laboratory, California Air Resources Board, NASA Ames Research Center, University of Colorado, Boulder, NOAA, California Institute of Technology
Journal of Geophysical Research: Atmospheres, 2018
Nitrous oxide (N2O) is a potent long‐lived greenhouse gas (GHG) and the strongest current emissio... more Nitrous oxide (N2O) is a potent long‐lived greenhouse gas (GHG) and the strongest current emissions of global anthropogenic stratospheric ozone depletion weighted by its ozone depletion potential. In California, N2O is the third largest contributor to the state's anthropogenic GHG emission inventory, though no study has quantified its statewide annual emissions through top‐down inverse modeling. Here we present the first annual (2013–2014) statewide top‐down estimates of anthropogenic N2O emissions. Utilizing continuous N2O observations from six sites across California in a hierarchical Bayesian inversion, we estimate that annual anthropogenic emissions are 1.5–2.5 times (at 95% confidence) the state inventory (41 Gg N2O in 2014). Without mitigation, this estimate represents 4–7% of total GHG emissions assuming that other reported GHG emissions are reasonably correct. This suggests that control of N2O could be an important component in meeting California's emission reduction...
Journal of Geophysical Research: Atmospheres, 2017
Atmospheric inverse estimates of gas emissions depend on transport model predictions, hence drivi... more Atmospheric inverse estimates of gas emissions depend on transport model predictions, hence driving a need to assess uncertainties in the transport model. In this study we assess the uncertainty in WRF‐STILT (Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport) model predictions using a combination of meteorological and carbon monoxide (CO) measurements. WRF configurations were selected to minimize meteorological biases using meteorological measurements of winds and boundary layer depths from surface stations and radar wind profiler sites across California. We compare model predictions with CO measurements from four tower sites in California from June 2013 through May 2014 to assess the seasonal biases and random errors in predicted CO mixing ratios. In general, the seasonal mean biases in boundary layer wind speed (< ~ 0.5 m/s), direction (< ~ 15°), and boundary layer height (< ~ 200 m) were small. However, random errors were large (~1.5–3.0 ...
Atmospheric Chemistry and Physics Discussions, 2016
We report continuous surface observations of carbon dioxide (CO 2) and methane (CH 4) from the Lo... more We report continuous surface observations of carbon dioxide (CO 2) and methane (CH 4) from the Los Angeles (LA) Megacity Carbon Project during 2015. We devised a calibration strategy, methods for selection of background air masses, calculation of urban enhancements, and a detailed algorithm for estimating uncertainties in urban scale CO 2 and CH 4 20 measurements. These methods are essential for understanding carbon fluxes from the LA megacity and other complex urban environments globally. We estimate background mole fractions entering LA using observations from four "extra-urban" sites including: two "coastal/marine" sites, one "continental" site in the high desert northeast of LA, and one "continental/midtroposphere" site located in the San Gabriel Mountains. We find that a local marine background can be established to within roughly 1 ppm CO 2 and 10 ppb CH 4 using these local measurement sites. We also show that continental sites may not be 25 relevant for selecting background observations during summer months due to the prevalence of onshore flow, which could transport CO 2 and CH 4 from the LA Basin to relatively remote sites. Overall, atmospheric carbon dioxide and methane levels are highly variable across Los Angeles. "Urban" and "suburban" sites show moderate to large CO 2 and CH 4 enhancements relative to a marine background to estimate. An urban site near Downtown LA has a median enhancement of roughly 20 ppm CO 2 and 150 ppb CH 4 during all hours, and roughly 15 ppm CO 2 and 80 ppb CH 4 during midday hours (roughly 12-30 16:00 LT, local time), which is the typical period of focus for flux inversions. The estimated measurement uncertainty is typically better than 0.1 ppm CO 2 and 1 ppb CH 4 based on the repeated standard gas measurements from the LA sites during the last 1-2 years, similar to Andrews et al. (2014). The largest component of the measurement uncertainty is due to the observations being elevated relative to the single-point calibration method; however the uncertainty in the background mole fraction is much larger than the measurement uncertainty. The approach to identifying background mole fractions described 35
Journal of Geophysical Research: Atmospheres, 2016
We present an analysis of methane (CH4) emissions using atmospheric observations from 13 sites in... more We present an analysis of methane (CH4) emissions using atmospheric observations from 13 sites in California during June 2013 to May 2014. A hierarchical Bayesian inversion method is used to estimate CH4 emissions for spatial regions (0.3° pixels for major regions) by comparing measured CH4 mixing ratios with transport model (Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport) predictions based on seasonally varying California‐specific CH4 prior emission models. The transport model is assessed using a combination of meteorological and carbon monoxide (CO) measurements coupled with the gridded California Air Resources Board (CARB) CO emission inventory. The hierarchical Bayesian inversion suggests that state annual anthropogenic CH4 emissions are 2.42 ± 0.49 Tg CH4/yr (at 95% confidence), higher (1.2–1.8 times) than the current CARB inventory (1.64 Tg CH4/yr in 2013). It should be noted that undiagnosed sources of errors or uncaptured errors in the mod...
In this document we show: (1) Estimates of epsilon (the slope component of the extrapolation unce... more In this document we show: (1) Estimates of epsilon (the slope component of the extrapolation uncertainty) for CO 2 and CH 4 based on laboratory measurements using CRDS analyzer units similar to those deployed in the field; (2) Uncertainty due to permeability of the Nafion drier determined from laboratory experiments; (3) Results from an Allan deviation analysis conducted using daily calibration runs from the LJO (La Jolla) analyzer during January 2016; (4) Example plots showing the CO 2 and CH 4 calibration baseline uncertainty using three possible time series of Picarro sensitivity for the standard tank measurements from the LJO site during January 2016. S1 Uncertainty due to Nafion drier permeability The laboratory experiments described here were performed at the Scripps Institution of Oceanography to estimate the uncertainty in the water vapor correction due to bias caused by the permeation of CO 2 and CH 4 across the membrane of the Nafion drier. We measured two dry standard tanks for 1200 seconds each, alternating one directly after the other. The measurement system setup was identical to those used at our field sites, with a Nafion dryer located upstream of the instrument. The water vapor concentrations at the start of the measurements were 0.095%, reflective of the Nafion dryer conditions during the ambient air measurements just prior to this experiment. As the measurements continued, the Nafion dryer gradually dried out, which reduced the permeation of CO 2 and CH 4 across the membrane. This effect leads to a small increase in the CO 2 and CH 4 levels measured on the Picarro analyzer (Figure S3). In this experiment we assume that other factors such as instrument drift are negligible over the duration of this experiment (approximately 16 hours). The uncertainty due to the Nafion permeation effect is derived from the slope of measured CO 2 , CH 4 concentrations against water vapor concentrations during our experiment, as shown in Figure S3. CO 2 concentrations are found to decrease at a ratio of-1.15 ppm per 1% change in water vapor concentration in the range of 0 to roughly 0.095%, while CH 4 concentrations are found to be small at a ratio of 0.029 ppb per 1% water vapor concentration change within a range of 0.03 to roughly 0.095%. As the water vapor concentrations in our field measurements lie within a range of 0.01±0.001%, we estimate the potential bias introduced by the 0.001% range in water vapor concentrations to be-0.0115 ppm for CO 2 and 0.000029 ppb for CH 4. Note that while the permeability of CH 4 through the Nafion membrane is shown to change dramatically in water vapor concentrations lower than 0.03%, this effect can be effectively ignored for our purposes considering the range of water vapor concentrations measured at our sites. Also, since the relationship between permeation through the Nafion membrane and water vapor concentration has been established, it is also possible to correct for this bias and report an uncertainty on the confidence of our understanding of this relationship. This correction may potentially be added in the future, which would further reduce the uncertainties due to this effect.
Solid waste management represents one of the largest anthropogenic methane emission sources. Howe... more Solid waste management represents one of the largest anthropogenic methane emission sources. However, precise quantification of landfill and composting emissions remains difficult due to variety of site-specific factors that contribute to landfill gas generation and effective capture. Remote sensing is an avenue to quantify process-level emissions from waste management facilities. The California Methane Survey flew the Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) over 270 landfills and 166 organic waste facilities repeatedly during 2016–2018 to quantify their contribution to the statewide methane budget. We use representative methane retrievals from this campaign to present three specific findings where remote sensing enabled better landfill and composting methane monitoring: (1) Quantification of strong point source emissions from the active face landfills that are difficult to capture by in situ monitoring or landfill models, (2) emissions that result...
Legislation in the State of California mandates reductions in emissions of short-lived climate po... more Legislation in the State of California mandates reductions in emissions of short-lived climate pollutants of 40% from 2013 levels by 2030 for CH 4. Identification of the sector(s) responsible for these emissions and their temporal and spatial variability is a key step in achieving these goals. Here, we determine the emissions of CH 4 in Los Angeles from 2011-2017 using a mountaintop remote sensing mapping spectrometer. We show that the pattern of CH 4 emissions contains both seasonal and nonseasonal contributions. We find that the seasonal component peaks in the winter and is correlated (R 2 = 0.58) with utility natural gas consumption from the residential and commercial sectors and not from the industrial and gas-fired power plant sectors. The nonseasonal component is (22.9 ± 1.4) Gg CH 4 /month. If the seasonal correlation is causal, about (1.4 ± 0.1)% of the commercial and residential natural gas consumption in Los Angeles is released into the atmosphere. Plain Language Summary CH 4 is a desirable target for greenhouse gas emission reductions because emission controls will have a rapid impact on radiative forcing. However, its emission budget is highly uncertain and poorly quantified. This paper reports new results from a novel mountaintop remote sensing spectrometer overlooking the Los Angeles basin. The study shows that the megacity's methane emissions are strongly correlated with the consumption of natural gas by residential and commercial consumers, with a leakage rate of (1.4 ± 0.1)%, while the nonseasonal component is (22.9 ± 1.4) Gg CH 4 / month. By identifying a clear relationship between CH 4 emissions and natural gas consumption, our results provide strong constraints on the pathways for fugitive CH 4 emissions from the natural gas distribution system in Los Angeles. Legislation in the State of California mandates reductions in emissions of short-lived climate pollutants of 40% from 2013 levels by 2030 for CH 4 (California Legislature, 2006). In the Los Angeles (LA) basin and other urban areas, previous studies focused on methane source attribution have used a variety of methods including C 2 H 6 as a tracer for fossil methane, and measurements of CH 4 isotopologues and VOCs to distinguish fossil and biogenic sources (
Atmospheric Chemistry and Physics Discussions, 2015
Large urban emissions of greenhouse gases result in large atmospheric enhancements relative to ba... more Large urban emissions of greenhouse gases result in large atmospheric enhancements relative to background that are easily measured. Using CO 2 mole fractions and ∆ 14 C and δ 13 C values of CO 2 in the Los Angeles megacity observed in inland Pasadena (2006-2013) and coastal Palos Verdes peninsula (autumn 2009-2013), we have determined time series for CO 2 contributions from fossil fuel combustion for both sites and broken those down into contributions from petroleum/gasoline and natural gas burning for Pasadena. We find a 10 % reduction in Pasadena CO 2 emissions from fossil fuel combustion during the Great Recession of 2008-2010, which is consistent with the bottom-up inventory determined by the California Air Resources Board. The isotopic variations and total atmospheric CO 2 from our observations are used to infer seasonality of natural gas and petroleum combustion. For natural gas, inferred emissions are out of phase with the seasonal cycle of total natural gas combustion seasonal patterns in bottom-up inventories but are consistent with the seasonality of natural gas usage by the area's electricity generating power plants. For petroleum, the inferred seasonality of CO 2 emissions from burning petroleum is delayed by several months relative to usage indicated by statewide gasoline taxes. Using the high-resolution Hestia-LA data product to compare emissions from parts of the basin sampled by winds at different times of year, we find that variations in observed fossil fuel CO 2 reflect seasonal variations in wind direction. The seasonality of the local CO 2 excess from fossil fuel combustion along the coast, on Palos Verdes peninsula, is higher in fall and winter than spring and summer, almost completely out of phase with that from Pasadena, also because of the annual variations of winds in the region. Variations in fossil fuel CO 2 signals are consistent with sampling the bottom-up Hestia-LA fossil CO 2 emissions product for sub-city source regions in the LA megacity domain when wind directions are considered.
Independent quantification of anthropogenic greenhouse gas (GHG) emission trends is a necessary f... more Independent quantification of anthropogenic greenhouse gas (GHG) emission trends is a necessary foundation for any GHG mitigation agreement. Atmospheric observations have the potential to provide objective information for monitoring, verifying, and validating anthropogenic GHG emissions. Over large spatial scales the biosphere's influence masks anthropogenic signals, obfuscating attribution. In comparison, megacities, with their large, localized GHG emissions forming characteristic urban domes, provide relatively easily detected anthropogenic atmospheric signals. Here we present the initial network design of a pilot program in Los Angeles (LA) as part of the Megacity Carbon project. The network is designed to sample carbon dioxide and methane distributions throughout the urban dome with a combination of in-situ point, slant column, and total column observations, providing a rich dataset for understanding urban emissions and distributions while simultaneously providing a baseline...
Future greenhouse gas (GHG) mitigation agreements will require independent quantification of anth... more Future greenhouse gas (GHG) mitigation agreements will require independent quantification of anthropogenic emission trends. Atmospheric observations contain information about true and total GHG emissions, and therefore provide a foundation for monitoring, verifying, and validating anthropogenic GHG emissions. Atmospheric observations also are strongly influenced by biospheric fluxes, presenting a challenge for disentanglement and attribution. Megacities provide an optimal target for atmospheric monitoring of human-derived emissions. Intense anthropogenic emissions are concentrated in small spatial areas, creating a strong and detectable local signal, facilitating observation and attribution. The Megacity Carbon project aims to capitalize on these strong signals, by developing and demonstrating atmospheric observing systems to track GHG emission trends. To quantitatively track emission changes with time, we must carefully consider observing network design. Here we present a modeling ...
Attributing observed CO 2 variations to human or natural cause is critical to deducing and tracki... more Attributing observed CO 2 variations to human or natural cause is critical to deducing and tracking emissions from observations. We have used in situ CO 2 , CO, and planetary boundary layer height (PBLH) measurements recorded during the CalNex-LA (CARB et al., 2008) ground campaign of 15 May-15 June 2010, in Pasadena, CA, to deduce the diurnally varying anthropogenic component of observed CO 2 in the megacity of Los Angeles (LA). This affordable and simple technique, validated by carbon isotope observations, is shown to robustly attribute observed CO 2 variation to anthropogenic or biogenic origin. During CalNex-LA, local fossil fuel combustion contributed up to ∼50 % of the observed CO 2 enhancement overnight, and ∼100 % during midday. This suggests midday column observations over LA, such as those made by satellites relying on reflected sunlight, can be used to track anthropogenic emissions.
Representations of the changing global carbon cycle under climatic and environmental perturbation... more Representations of the changing global carbon cycle under climatic and environmental perturbations require highly detailed accounting of all atmosphere and biosphere exchange. These fluxes remain unsatisfactory, as a consequence of only having data with limited spatiotemporal coverage and precision, which restrict accurate assessments. Through the nature of intimate coupling of global carbon and oxygen cycles via O 2 and CO 2 and their unique triple oxygen isotope compositions in the biosphere and atmosphere, greater insight is available. We report analysis of their isotopic compositions with the widest geographical and temporal coverage (123 new measurements for CO 2 ) and constrain, on an annual basis, the global CO 2 recycling time (1.5 ± 0.2 year) and gross primary productivities of terrestrial (~ 170-200 PgC/year) and oceanic (~ 90-120 PgC/year) biospheres. Observed inter-annual variations in CO 2 triple oxygen isotopic compositions were observed at a magnitude close to the largest contrast set by the terrestrial and oceanic biospheres. The seasonal cycles between the east and west Pacific Ocean were found to be drastically different. This intraannual variability implies that the entire atmospheric CO 2 turnover time is not much longer than the tropospheric mixing time (less than ~ 5 months), verifying the derived recycling time. The new measurements, analyses, and incorporation of other global data sets allow development of an independent approach, providing a strong constraint to biogeochemical models. Imbalance between CO 2 sources and sinks results in increasing atmospheric CO 2 levels 1-3 . The increase is due mainly to fossil fuel burning, emitting at an average rate of 9.4 ± 0.5 PgC/year 2 . As a consequence, the average global temperature has increased by 1.1 °C3 . The combined effect of elevated atmospheric CO 2 levels and temperature leads to observable changes in the global carbon cycle . A number of efforts have been used to quantify the changes of the carbon cycles in response to changing environments . Climate models coupled with biogeochemical modules are frequently used to assess changing ecosystems in the context of changing climate . However, it has been noted that current knowledge is insufficient to simulate and project the ecosystem responses 6,7 , owing to the boundaries of our knowledge of the gross processes. Reviewing the input components and processes considered , terrestrial net ecosystem exchange (NEE) is better studied but gross primary production (GPP) processes (such as photosynthesis) comprising > 3/4 of the total carbon fluxes in the carbon cycling budget remain least well-constrained 8,10-18 . The incomplete knowledge of the gross processes is largely due to rapid hydration and dehydration of CO 2 occurring in chloroplasts; it is also because of this fast reaction that regional and global assessments of the gross components are possible . The carbonic anhydrase
The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution ... more The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution spectra of reflected sunlight in three near-infrared bands centered around 0.76, 1.6, and 2.3 µm and to deliver simultaneous retrievals of column-averaged dry air mole fractions of CO 2 , CH 4 , CO, and H 2 O (denoted XCO 2 , XCH 4 , XCO, and XH 2 O, respectively) at different times of day over North America. In this study, we perform radiative transfer simulations over both clear-sky and all-sky scenes expected to be observed by GeoFTS and estimate the prospective performance of retrievals based on results from Bayesian error analysis and characterization. We find that, for simulated clear-sky retrievals, the average retrieval biases and single-measurement precisions are < 0.2 % for XCO 2 , XCH 4 , and XH 2 O, and < 2 % for XCO, when the a priori values have a bias of 3 % and an uncertainty of 3 %. In addition, an increase in the amount of aerosols and ice clouds leads to a notable increase in the retrieval biases and slight worsening of the retrieval precisions. Furthermore, retrieval precision is a strong function of signal-to-noise ratio and spectral resolution. This simulation study can help guide decisions on the design of the GeoFTS observing system, which can result in cost-effective measurement strategies while achieving satisfactory levels of retrieval precisions and biases. The simultaneous retrievals at different times of day will be important for more accurate estimation of carbon sources and sinks on fine spatiotemporal scales and for studies related to the atmospheric component of the water cycle.
Beryllium-7 ( 7 Be), produced by the interaction of cosmic radiation with atoms and molecules pri... more Beryllium-7 ( 7 Be), produced by the interaction of cosmic radiation with atoms and molecules primarily in the upper troposphere and lower stratosphere, provides a useful tracer of cross-tropopause transport and vertical mixing in the troposphere. In the western Pacific subtropical region, the interaction of the subtropical jet stream with monsoon systems potentially enhances the transport. Here, we report one year of 7 Be measurements at daily resolution during 2010, at Mt. Lulin (2862 m above mean sea level; NOAA code: LLN), along with other gaseous compounds such as O 3 and CO and meteorological information, to assess processes that affect the variability of 7 Be. The 7 Be concentrations are of the order 1 mBq/m 3 or less. The 7 Be activity is generally low during summer, largely due to precipitation and unfavorable conditions of atmospheric dynamics (i.e., prevalence of upward motion), but it is occasionally high because of the influence of typhoons. In winter and spring, stratospheric effects observed at the surface were frequent and significant, thereby directly affecting the strength of stratospheric effects on the troposphere, such as the tropospheric oxidation capacity. The effects of the stratospheric intrusions are seen by negative and positive correlations of 7 Be with relative humidity and concentration of O 3 , respectively. The stratospheric effect is further supported by the presence of downwelling transport in this region in the European Centre for Medium-Range Weather Forecasts-Atmospheric Composition Reanalysis Version 4 CO, O 3 , and relative humidity data.
Eleven glasses recovered from Holes 786A and 786B were fresh enough for volatile analysis by infr... more Eleven glasses recovered from Holes 786A and 786B were fresh enough for volatile analysis by infrared spectroscopy. The compositions of these glasses range from boninitic to rhyolitic. The glasses from the boninites contain 1.4 to 1.7 wt% H 2 O, while the rhyolitic glasses contain 2 to 6 wt% H 2 O, and all glasses have less than 30 to 40 ppm CO 2 . The highest H 2 O contents are probably the result of seawater alteration. The unaltered dacitic to rhyolitic glasses were probably quenched at low pressures corresponding to depths of 0-700 m below the seafloor, also corresponding to the depths of collection of these samples, although the water depths may have been different between the Eocene and the present. The lower boninitic H 2 O contents in vesicular glasses suggest shallow quenching on the seafloor.
Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as ... more Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as carbon dioxide (CO2) and methane (CH4) that contribute to modern-day climate change. As such, a growing number of urban policymakers and stakeholders are adopting emission reduction targets and implementing policies to reach those targets. Over the past two decades research teams have established urban GHG monitoring networks to determine how much, where, and why a particular city emits GHGs, and to track changes in emissions over time. Coordination among these efforts has been limited, restricting the scope of analyses and insights. Here we present a harmonized data set synthesizing urban GHG observations from cities with monitoring networks across North America that will facilitate cross-city analyses and address scientific questions that are difficult to address in isolation.
California has been in a severe drought for five years affec5ng weather, vegeta5on, and policy. U... more California has been in a severe drought for five years affec5ng weather, vegeta5on, and policy. Unfortunately, the last year’s strong El Nino condi5ons did not bring the expected extra rainfall relief to southern California, and we are just finishing a year of water ra5oning, concentra5ng on limi5ng irriga5on of outdoor landscape. What changes in the atmospheric CO2 composi5on in the Los Angeles, CA (LA) megacity have occurred during this period? We inves5gate changes reflected in the radiocarbon (ΔC) and stable carbon isotopic composi5on (δC) of the CO2 in LA, using the long-‐term flask sample record at our Pasadena (18 years, 11 with Δ14C; samples collected on alternate aXernoons at 14:00 PST) site (Fig. 1) to put the last five years in context. Pasadena is inland and a good receptor site for emissions in the LA basin for much of the year when the prevailing winds are from the ocean passing over LA. Radiocarbon measurements give informa5on on the fossil fuel and biosphere compone...
H.D. Graven, T. Lueker, M. Fischer, K. Brophy, T. Guilderson, R. Keeling, T. Arnold, R. Bambha, W... more H.D. Graven, T. Lueker, M. Fischer, K. Brophy, T. Guilderson, R. Keeling, T. Arnold, R. Bambha, W. Callahan, E. Campbell, C. Frankenberg, Y. Hsu, L. Iraci, S. Jeong, J. Kim, B. LaFranchi, S. Lehman, A. Manning, H. Michelson, J. Miller, S. Newman, W. Paplawsky, N. Parazoo, C. Sloop, S. Walker, M. Whelan, D. Wunch Imperial College London, Scripps Institution of Oceanography, Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, Met Office Hadley Centre, Sandia National Laboratory, Earth Networks, University of California, Merced, NASA Jet Propulsion Laboratory, California Air Resources Board, NASA Ames Research Center, University of Colorado, Boulder, NOAA, California Institute of Technology
Journal of Geophysical Research: Atmospheres, 2018
Nitrous oxide (N2O) is a potent long‐lived greenhouse gas (GHG) and the strongest current emissio... more Nitrous oxide (N2O) is a potent long‐lived greenhouse gas (GHG) and the strongest current emissions of global anthropogenic stratospheric ozone depletion weighted by its ozone depletion potential. In California, N2O is the third largest contributor to the state's anthropogenic GHG emission inventory, though no study has quantified its statewide annual emissions through top‐down inverse modeling. Here we present the first annual (2013–2014) statewide top‐down estimates of anthropogenic N2O emissions. Utilizing continuous N2O observations from six sites across California in a hierarchical Bayesian inversion, we estimate that annual anthropogenic emissions are 1.5–2.5 times (at 95% confidence) the state inventory (41 Gg N2O in 2014). Without mitigation, this estimate represents 4–7% of total GHG emissions assuming that other reported GHG emissions are reasonably correct. This suggests that control of N2O could be an important component in meeting California's emission reduction...
Journal of Geophysical Research: Atmospheres, 2017
Atmospheric inverse estimates of gas emissions depend on transport model predictions, hence drivi... more Atmospheric inverse estimates of gas emissions depend on transport model predictions, hence driving a need to assess uncertainties in the transport model. In this study we assess the uncertainty in WRF‐STILT (Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport) model predictions using a combination of meteorological and carbon monoxide (CO) measurements. WRF configurations were selected to minimize meteorological biases using meteorological measurements of winds and boundary layer depths from surface stations and radar wind profiler sites across California. We compare model predictions with CO measurements from four tower sites in California from June 2013 through May 2014 to assess the seasonal biases and random errors in predicted CO mixing ratios. In general, the seasonal mean biases in boundary layer wind speed (< ~ 0.5 m/s), direction (< ~ 15°), and boundary layer height (< ~ 200 m) were small. However, random errors were large (~1.5–3.0 ...
Atmospheric Chemistry and Physics Discussions, 2016
We report continuous surface observations of carbon dioxide (CO 2) and methane (CH 4) from the Lo... more We report continuous surface observations of carbon dioxide (CO 2) and methane (CH 4) from the Los Angeles (LA) Megacity Carbon Project during 2015. We devised a calibration strategy, methods for selection of background air masses, calculation of urban enhancements, and a detailed algorithm for estimating uncertainties in urban scale CO 2 and CH 4 20 measurements. These methods are essential for understanding carbon fluxes from the LA megacity and other complex urban environments globally. We estimate background mole fractions entering LA using observations from four "extra-urban" sites including: two "coastal/marine" sites, one "continental" site in the high desert northeast of LA, and one "continental/midtroposphere" site located in the San Gabriel Mountains. We find that a local marine background can be established to within roughly 1 ppm CO 2 and 10 ppb CH 4 using these local measurement sites. We also show that continental sites may not be 25 relevant for selecting background observations during summer months due to the prevalence of onshore flow, which could transport CO 2 and CH 4 from the LA Basin to relatively remote sites. Overall, atmospheric carbon dioxide and methane levels are highly variable across Los Angeles. "Urban" and "suburban" sites show moderate to large CO 2 and CH 4 enhancements relative to a marine background to estimate. An urban site near Downtown LA has a median enhancement of roughly 20 ppm CO 2 and 150 ppb CH 4 during all hours, and roughly 15 ppm CO 2 and 80 ppb CH 4 during midday hours (roughly 12-30 16:00 LT, local time), which is the typical period of focus for flux inversions. The estimated measurement uncertainty is typically better than 0.1 ppm CO 2 and 1 ppb CH 4 based on the repeated standard gas measurements from the LA sites during the last 1-2 years, similar to Andrews et al. (2014). The largest component of the measurement uncertainty is due to the observations being elevated relative to the single-point calibration method; however the uncertainty in the background mole fraction is much larger than the measurement uncertainty. The approach to identifying background mole fractions described 35
Journal of Geophysical Research: Atmospheres, 2016
We present an analysis of methane (CH4) emissions using atmospheric observations from 13 sites in... more We present an analysis of methane (CH4) emissions using atmospheric observations from 13 sites in California during June 2013 to May 2014. A hierarchical Bayesian inversion method is used to estimate CH4 emissions for spatial regions (0.3° pixels for major regions) by comparing measured CH4 mixing ratios with transport model (Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport) predictions based on seasonally varying California‐specific CH4 prior emission models. The transport model is assessed using a combination of meteorological and carbon monoxide (CO) measurements coupled with the gridded California Air Resources Board (CARB) CO emission inventory. The hierarchical Bayesian inversion suggests that state annual anthropogenic CH4 emissions are 2.42 ± 0.49 Tg CH4/yr (at 95% confidence), higher (1.2–1.8 times) than the current CARB inventory (1.64 Tg CH4/yr in 2013). It should be noted that undiagnosed sources of errors or uncaptured errors in the mod...
In this document we show: (1) Estimates of epsilon (the slope component of the extrapolation unce... more In this document we show: (1) Estimates of epsilon (the slope component of the extrapolation uncertainty) for CO 2 and CH 4 based on laboratory measurements using CRDS analyzer units similar to those deployed in the field; (2) Uncertainty due to permeability of the Nafion drier determined from laboratory experiments; (3) Results from an Allan deviation analysis conducted using daily calibration runs from the LJO (La Jolla) analyzer during January 2016; (4) Example plots showing the CO 2 and CH 4 calibration baseline uncertainty using three possible time series of Picarro sensitivity for the standard tank measurements from the LJO site during January 2016. S1 Uncertainty due to Nafion drier permeability The laboratory experiments described here were performed at the Scripps Institution of Oceanography to estimate the uncertainty in the water vapor correction due to bias caused by the permeation of CO 2 and CH 4 across the membrane of the Nafion drier. We measured two dry standard tanks for 1200 seconds each, alternating one directly after the other. The measurement system setup was identical to those used at our field sites, with a Nafion dryer located upstream of the instrument. The water vapor concentrations at the start of the measurements were 0.095%, reflective of the Nafion dryer conditions during the ambient air measurements just prior to this experiment. As the measurements continued, the Nafion dryer gradually dried out, which reduced the permeation of CO 2 and CH 4 across the membrane. This effect leads to a small increase in the CO 2 and CH 4 levels measured on the Picarro analyzer (Figure S3). In this experiment we assume that other factors such as instrument drift are negligible over the duration of this experiment (approximately 16 hours). The uncertainty due to the Nafion permeation effect is derived from the slope of measured CO 2 , CH 4 concentrations against water vapor concentrations during our experiment, as shown in Figure S3. CO 2 concentrations are found to decrease at a ratio of-1.15 ppm per 1% change in water vapor concentration in the range of 0 to roughly 0.095%, while CH 4 concentrations are found to be small at a ratio of 0.029 ppb per 1% water vapor concentration change within a range of 0.03 to roughly 0.095%. As the water vapor concentrations in our field measurements lie within a range of 0.01±0.001%, we estimate the potential bias introduced by the 0.001% range in water vapor concentrations to be-0.0115 ppm for CO 2 and 0.000029 ppb for CH 4. Note that while the permeability of CH 4 through the Nafion membrane is shown to change dramatically in water vapor concentrations lower than 0.03%, this effect can be effectively ignored for our purposes considering the range of water vapor concentrations measured at our sites. Also, since the relationship between permeation through the Nafion membrane and water vapor concentration has been established, it is also possible to correct for this bias and report an uncertainty on the confidence of our understanding of this relationship. This correction may potentially be added in the future, which would further reduce the uncertainties due to this effect.
Solid waste management represents one of the largest anthropogenic methane emission sources. Howe... more Solid waste management represents one of the largest anthropogenic methane emission sources. However, precise quantification of landfill and composting emissions remains difficult due to variety of site-specific factors that contribute to landfill gas generation and effective capture. Remote sensing is an avenue to quantify process-level emissions from waste management facilities. The California Methane Survey flew the Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) over 270 landfills and 166 organic waste facilities repeatedly during 2016–2018 to quantify their contribution to the statewide methane budget. We use representative methane retrievals from this campaign to present three specific findings where remote sensing enabled better landfill and composting methane monitoring: (1) Quantification of strong point source emissions from the active face landfills that are difficult to capture by in situ monitoring or landfill models, (2) emissions that result...
Legislation in the State of California mandates reductions in emissions of short-lived climate po... more Legislation in the State of California mandates reductions in emissions of short-lived climate pollutants of 40% from 2013 levels by 2030 for CH 4. Identification of the sector(s) responsible for these emissions and their temporal and spatial variability is a key step in achieving these goals. Here, we determine the emissions of CH 4 in Los Angeles from 2011-2017 using a mountaintop remote sensing mapping spectrometer. We show that the pattern of CH 4 emissions contains both seasonal and nonseasonal contributions. We find that the seasonal component peaks in the winter and is correlated (R 2 = 0.58) with utility natural gas consumption from the residential and commercial sectors and not from the industrial and gas-fired power plant sectors. The nonseasonal component is (22.9 ± 1.4) Gg CH 4 /month. If the seasonal correlation is causal, about (1.4 ± 0.1)% of the commercial and residential natural gas consumption in Los Angeles is released into the atmosphere. Plain Language Summary CH 4 is a desirable target for greenhouse gas emission reductions because emission controls will have a rapid impact on radiative forcing. However, its emission budget is highly uncertain and poorly quantified. This paper reports new results from a novel mountaintop remote sensing spectrometer overlooking the Los Angeles basin. The study shows that the megacity's methane emissions are strongly correlated with the consumption of natural gas by residential and commercial consumers, with a leakage rate of (1.4 ± 0.1)%, while the nonseasonal component is (22.9 ± 1.4) Gg CH 4 / month. By identifying a clear relationship between CH 4 emissions and natural gas consumption, our results provide strong constraints on the pathways for fugitive CH 4 emissions from the natural gas distribution system in Los Angeles. Legislation in the State of California mandates reductions in emissions of short-lived climate pollutants of 40% from 2013 levels by 2030 for CH 4 (California Legislature, 2006). In the Los Angeles (LA) basin and other urban areas, previous studies focused on methane source attribution have used a variety of methods including C 2 H 6 as a tracer for fossil methane, and measurements of CH 4 isotopologues and VOCs to distinguish fossil and biogenic sources (
Atmospheric Chemistry and Physics Discussions, 2015
Large urban emissions of greenhouse gases result in large atmospheric enhancements relative to ba... more Large urban emissions of greenhouse gases result in large atmospheric enhancements relative to background that are easily measured. Using CO 2 mole fractions and ∆ 14 C and δ 13 C values of CO 2 in the Los Angeles megacity observed in inland Pasadena (2006-2013) and coastal Palos Verdes peninsula (autumn 2009-2013), we have determined time series for CO 2 contributions from fossil fuel combustion for both sites and broken those down into contributions from petroleum/gasoline and natural gas burning for Pasadena. We find a 10 % reduction in Pasadena CO 2 emissions from fossil fuel combustion during the Great Recession of 2008-2010, which is consistent with the bottom-up inventory determined by the California Air Resources Board. The isotopic variations and total atmospheric CO 2 from our observations are used to infer seasonality of natural gas and petroleum combustion. For natural gas, inferred emissions are out of phase with the seasonal cycle of total natural gas combustion seasonal patterns in bottom-up inventories but are consistent with the seasonality of natural gas usage by the area's electricity generating power plants. For petroleum, the inferred seasonality of CO 2 emissions from burning petroleum is delayed by several months relative to usage indicated by statewide gasoline taxes. Using the high-resolution Hestia-LA data product to compare emissions from parts of the basin sampled by winds at different times of year, we find that variations in observed fossil fuel CO 2 reflect seasonal variations in wind direction. The seasonality of the local CO 2 excess from fossil fuel combustion along the coast, on Palos Verdes peninsula, is higher in fall and winter than spring and summer, almost completely out of phase with that from Pasadena, also because of the annual variations of winds in the region. Variations in fossil fuel CO 2 signals are consistent with sampling the bottom-up Hestia-LA fossil CO 2 emissions product for sub-city source regions in the LA megacity domain when wind directions are considered.
Independent quantification of anthropogenic greenhouse gas (GHG) emission trends is a necessary f... more Independent quantification of anthropogenic greenhouse gas (GHG) emission trends is a necessary foundation for any GHG mitigation agreement. Atmospheric observations have the potential to provide objective information for monitoring, verifying, and validating anthropogenic GHG emissions. Over large spatial scales the biosphere's influence masks anthropogenic signals, obfuscating attribution. In comparison, megacities, with their large, localized GHG emissions forming characteristic urban domes, provide relatively easily detected anthropogenic atmospheric signals. Here we present the initial network design of a pilot program in Los Angeles (LA) as part of the Megacity Carbon project. The network is designed to sample carbon dioxide and methane distributions throughout the urban dome with a combination of in-situ point, slant column, and total column observations, providing a rich dataset for understanding urban emissions and distributions while simultaneously providing a baseline...
Future greenhouse gas (GHG) mitigation agreements will require independent quantification of anth... more Future greenhouse gas (GHG) mitigation agreements will require independent quantification of anthropogenic emission trends. Atmospheric observations contain information about true and total GHG emissions, and therefore provide a foundation for monitoring, verifying, and validating anthropogenic GHG emissions. Atmospheric observations also are strongly influenced by biospheric fluxes, presenting a challenge for disentanglement and attribution. Megacities provide an optimal target for atmospheric monitoring of human-derived emissions. Intense anthropogenic emissions are concentrated in small spatial areas, creating a strong and detectable local signal, facilitating observation and attribution. The Megacity Carbon project aims to capitalize on these strong signals, by developing and demonstrating atmospheric observing systems to track GHG emission trends. To quantitatively track emission changes with time, we must carefully consider observing network design. Here we present a modeling ...
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Papers by Sally Newman