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Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical–meteorological interactions that drive high-pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in western U.S. basins. Approximately 120 people participated, representing 50 institutions and five countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological–chemical linkages outlined here, nor to validate complex processes within coupled atmosphere–chemistry models.

20 pags., 11 figs. 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0, Fluxes of halogenated volatile organic compounds (VOCs) over the Southern Ocean remain poorly understood, and few atmospheric measurements exist to constrain modeled emissions of these compounds. We present observations of CHBr, CHBr, CHI, CHClBr, CHBrCl, and CHBr during the O2=N Ratio and CO Airborne Southern Ocean (ORCAS) study and the second Atmospheric Tomography mission (ATom-2) in January and February of 2016 and 2017. Good model-measurement correlations were obtained between these observations and simulations from the Community Earth System Model (CESM) atmospheric component with chemistry (CAM-Chem) for CHBr, CHBr, CHI, and CHClBr but all showed significant differences in model: measurement ratios. The model: measurement comparison for CHBr was satisfactory and for CHBrCl the low levels present precluded us from making a complete assessment. Thereafter, we demonstrate two novel approaches to estimate halogenated VOC fluxes; the first approach takes advantage of the robust relationships that were found between airborne observations of O and CHBr, CHBr, and CHClBr. We use these linear regressions with O and modeled O distributions to infer a biological flux of halogenated VOCs. The second approach uses the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model to explore the relationships between observed mixing ratios and the product of the upstream surface influence of sea ice, chl a, absorption due to detritus, and downward shortwave radiation at the surface, which in turn relate to various regional hypothesized sources of halogenated VOCs such as marine phytoplankton, phytoplankton in seaice brines, and decomposing organic matter in surface seawater. These relationships can help evaluate the likelihood of particular halogenated VOC sources and in the case of statistically significant correlations, such as was found for CHI, may be used to derive an estimated flux field. Our results are consistent with a biogenic regional source of CHBr and both nonbiological and biological sources of CHI over these regions., We would like to thank the ORCAS and ATom-2 science teams as well as the NCAR Research Aviation Facility and NASA DC-8 pilots, technicians, and mechanics for their support during the field campaigns. This work was made possible by grants from NSF Polar Programs (1501993, 1501997, 1501292, 1502301, 1543457), NSF Atmospheric Chemistry grants 1535364, 1623745, and 1623748, and NASA funding of the EVS2 Atmospheric Tomography (ATom) project, as well as the support of the NCAR Advanced Study Program (ASP) Postdoctoral Fellowship Program and computing support from Yellowstone, provided by NCAR’s Computational and Information Systems Laboratory. The National Center for Atmospheric Research is sponsored by the National Science Foundation. Financial support.

Cities are concentrated areas of CO2 emissions and have become the foci of policies for mitigation actions. However, atmospheric measurement networks suitable for evaluating urban emissions over time are scarce. Here we present a unique long-term (decadal) record of CO2 mole fractions from five sites across Utah's metropolitan Salt Lake Valley. We examine "excess" CO2 above background conditions resulting from local emissions and meteorological conditions. We ascribe CO2 trends to changes in emissions, since we did not find long-term trends in atmospheric mixing proxies. Three contrasting CO2 trends emerged across urban types: negative trends at a residential-industrial site, positive trends at a site surrounded by rapid suburban growth, and relatively constant CO2 over time at multiple sites in the established, residential, and commercial urban core. Analysis of population within the atmospheric footprints of the different sites reveals approximately equal increases in population influencing the observed CO2, implying a nonlinear relationship with CO2 emissions: Population growth in rural areas that experienced suburban development was associated with increasing emissions while population growth in the developed urban core was associated with stable emissions. Four state-of-the-art global-scale emission inventories also have a nonlinear relationship with population density across the city; however, in contrast to our observations, they all have nearly constant emissions over time. Our results indicate that decadal scale changes in urban CO2 emissions are detectable through monitoring networks and constitute a valuable approach to evaluate emission inventories and studies of urban carbon cycles.

The Southern Ocean plays a critical role in the global climate system by mediating atmosphere–ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air–sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings.

We present observations of CHBr3, CH2Br2, CH3I, CHClBr2, and CHBrCl2 from the Trace Gas Organic Analyzer (TOGA) during the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study and the 2nd Atmospheric Tomography mission (ATom-2), in January and February of 2016 and 2017. We also use CH3Br from the University of Miami Advanced Whole Air Sampler (AWAS) on ORCAS and from the UC Irvine Whole Air Sampler (WAS) on ATom-2. We compare our observations with simulations from the Community Atmosphere Model with Chemistry (CAM-Chem). We report regional enrichment ratios of CHBr3 and CH2Br2 to O2 of 0.19 ± 0.01, and 0.07 ± 0.004 pmol : mol, poleward of 60° S between 180° W and 55° W, and of 0.32 ± 0.02, 0.07 ± 0.004 pmol : mol over the Patagonian Shelf, between 40° S and 55° S and between 70° W and 55° W where we also report enrichment ratios of CH3I to O2 of 0.38 ± 0.03 pmol : mol and of CH2ClBr2 to O2 of 0.19 ± 0.04 pmol: mol. Using the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model, we use correlations between halogenated hydrocarbon mixing ratios and the upwind influences of chlorophyll a, sea ice, solar radiation, and dissolved organic material to investigate previously hypothesized sources of halogenated volatile organic compounds (HVOCs) in the southern high latitudes. Our results are consistent with a biogenic regional source of CHBr3, and both non-biological and biological sources of CH3I over these regions, but do not corroborate a regional sea-ice source of HVOCs in January and February. Based on these relationships, we estimate the average two-month (Jan.-Feb.) emissions poleward of 60° S between 180° W and 55° W of CHBr3, CH2Br2, CH3I, and CHClBr2 to be 91 ± 8, 31 ± 17, 35 ± 29, and 11 ± 4 pmol m−2 hr−1, and regional emissions of these gases over the Patagonian Shelf to be 329 ± 23, 69 ± 5, 392 ± 32, 24 ± 4 pmol m−2 hr−1 respectively.

Despite its importance to the climate system, the ocean meridional heat transport is still poorly quantified. We identify a strong link between the northern hemisphere deficit in atmospheric potential oxygen (APO = O $$_2$$ + 1.1 $$\times$$ CO $$_2$$ ) and the asymmetry in meridional heat transport between northern and southern hemispheres. The recent aircraft observations from the HIPPO campaign reveal a northern APO deficit in the tropospheric column of $$-$$ 10.4 $$\pm$$ 1.0 per meg, double the value at the surface and more representative of large-scale air–sea fluxes. The global northward ocean heat transport asymmetry necessary to explain the observed APO deficit is about 0.7–1.1 PW, which corresponds to the upper range of estimates from hydrographic sections and atmospheric reanalyses.

Measurements of atmospheric CO2 concentration provide a tight constraint on the sum of the land and ocean sinks. This constraint has been combined with estimates of ocean carbon flux and riverine transport of carbon from land to oceans to isolate the land sink. Uncertainties in the ocean and river fluxes therefore translate into uncertainties in the land sink. Here, we introduce a heat-based constraint on the latitudinal distribution of ocean and river carbon fluxes, and reassess the partition between ocean, river and land in the tropics, and in the southern and northern extra-tropics. We show that the ocean overturning circulation and biological pump tightly link the ocean transports of heat and carbon between hemispheres. Using this coupling between heat and carbon, we derive ocean and river carbon fluxes compatible with observational constraints on heat transport. This heat-based constraint requires a 20–100% stronger ocean and river carbon transport from the Northern Hemisphere to the Southern Hemisphere than existing estimates, and supports an upward revision of the global riverine carbon flux from 0.45 to 0.78 PgC yr−1. These systematic biases in existing ocean/river carbon fluxes redistribute up to 40% of the carbon sink between northern, tropical and southern land ecosystems. As a consequence, the magnitude of both the southern land source and the northern land sink may have to be substantially reduced. Terrestrial carbon sources in the Southern Hemisphere and sinks in the Northern Hemisphere may be smaller than thought, according to a recalculation that accounts for the oceanic redistribution of carbon.

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.

In remote regions such as the open Southern Ocean, satellite observations often provide the only available tool with which to evaluate large-scale biogeochemical processes. However, these observations need to be carefully evaluated with in situ measurements. With an average of 20 crossings per year from 2002 to 2011, the Drake Passage Time-series (DPT) represents one of the most complete datasets of biogeochemical measurements in the open Southern Ocean. This dataset offers a unique opportunity to validate satellite-based productivity algorithms and to improve understanding of the role of this region in the global carbon cycle. Net community production (NCP) was estimated using discrete measurements of total dissolved inorganic carbon (TCO2) and phosphate ( PO 4 3 − ), and high-frequency underway measurements of the partial pressure of carbon dioxide in the surface ocean (pCO2surf) from the DPT, combined with estimates of gas exchange, Ekman transport, wind stress curl, and vertical entrainment. We estimate annual NCP using seasonal PO 4 3 − ( NCP PO 4 3 − ) and TCO2 ( NCP TCO 2 ) budgets of 1.2±0.7 and 1.6±0.4 mol C m−2 yr−1, respectively. Budget terms for gas exchange, entrainment, and advective supply indicate that a closed system seasonal-drawdown approach that does not consider additional terms may underestimate NCP in this region by nearly 35%. NCP estimates are compared to satellite algorithms commonly used to estimate both net primary production (NPP) and organic carbon export. Budget-based NCP approaches indicate high rates of NCP during austral spring with little additional NCP over austral summer. In contrast, satellite approaches suggest a more gradual increase and decline in NCP rates over the growing season with approximately 40% of NCP accumulating during austral summer.

We present an evaluation of aircraft observations of the carbon and greenhouse gases CO2, CH4, N2O, and CO using a direct-absorption pulsed quantum cascade laser spectrometer (QCLS) operated during the HIPPO and CalNex airborne experiments. The QCLS made continuous 1 Hz measurements with 1σ Allan precisions of 20, 0.5, 0.09, and 0.15 ppb for CO2, CH4, N2O, and CO, respectively, over > 500 flight hours on 79 research flights. The QCLS measurements are compared to two vacuum ultraviolet (VUV) CO instruments (CalNex and HIPPO), a cavity ring-down spectrometer (CRDS) measuring CO2 and CH4 (CalNex), two broadband non-dispersive infrared (NDIR) spectrometers measuring CO2 (HIPPO), two onboard gas chromatographs measuring a variety of chemical species including CH4, N2O, and CO (HIPPO), and various flask-based measurements of all four species. QCLS measurements are tied to NOAA and WMO standards using an in-flight calibration system, and mean differences when compared to NOAA CCG flask data over the 59 HIPPO research flights were 100, 1, 1, and 2 ppb for CO2, CH4, N2O, and CO, respectively. The details of the end-to-end calibration procedures and the data quality assurance and quality control (QA/QC) are presented. Specifically, we discuss our practices for the traceability of standards given uncertainties in calibration cylinders, isotopic and surface effects for the long-lived greenhouse gas tracers, interpolation techniques for in-flight calibrations, and the effects of instrument linearity on retrieved mole fractions.

Observations of methyl chloroform combined with an atmospheric transport model predict a Northern to Southern Hemisphere hydroxyl ratio of slightly less than 1, whereas commonly used atmospheric chemistry models predict ratios 15–45% higher. The hydroxyl radical is an important atmospheric oxidant, but our knowledge of its global distribution remains imprecise, with estimates for the ratio of Northern Hemisphere to Southern Hemisphere hydroxyl radical concentration varying from 0.85 to 1.4. These authors use a three-dimensional chemistry-transport model that has been well validated for interhemispheric transport using sulphur hexafluoride measurements, to obtain an interhemispheric hydroxyl radical ratio of 0.97±0.12. This information can help improve our understanding of the fate of atmospheric pollutants and greenhouse gases. The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere1,2,3. The ratio of Northern Hemispheric to Southern Hemispheric (NH/SH) OH concentration is important for our understanding of emission estimates of atmospheric species such as nitrogen oxides and methane4,5,6. It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4, 7,8,9,10). Here we determine the NH/SH ratio of OH with the help of methyl chloroform data (a proxy for OH concentrations) and an atmospheric transport model that accurately describes interhemispheric transport and modelled emissions. We find that for the years 2004–2011 the model predicts an annual mean NH–SH gradient of methyl chloroform that is a tight linear function of the modelled NH/SH ratio in annual mean OH. We estimate a NH/SH OH ratio of 0.97 ± 0.12 during this time period by optimizing global total emissions and mean OH abundance to fit methyl chloroform data from two surface-measurement networks and aircraft campaigns11,12,13. Our findings suggest that top-down emission estimates of reactive species such as nitrogen oxides in key emitting countries in the NH that are based on a NH/SH OH ratio larger than 1 may be overestimated.

A single particle soot photometer (SP2) was operated on the NCAR C-130 during the MIRAGE campaign (part of MILAGRO), sampling black carbon (BC) over Mexico. The highest BC concentrations were measured over Mexico City (sometimes as much as 2 μg/m3) and over hill-fires to the south of the city. The age of plumes outside of Mexico City was determined using a combination of HYSPLIT trajectories, WRF-FLEXPART modeling and CMET balloon tracks. As expected, older, diluted air masses had lower BC concentrations. A comparison of carbon monoxide (CO) and BC suggests a CO background of around 65 ppbv, and a background-corrected BC/COnet ratio of 2.89±0.89 (ng/m3-STP)/ppbv (average ± standard deviation). This ratio is similar for fresh emissions over Mexico City, as well as for aged airmasses. Comparison of light absorption measured with a particle soot absorption photometer (PSAP) and the SP2 BC suggests a BC mass-normalized absorption cross-section (MAC) of 10.9±2.1 m2/g at 660 nm (or 13.1 m2/g @ 550 nm, assuming MAC is inversely dependent on wavelength). This appears independent of aging and similar to the expected absorption cross-section for aged BC, but values, particularly in fresh emissions, could be biased high due to instrument artifacts. SP2-derived BC coating indicators show a prominent thinly-coated BC mode over the Mexico City Metropolitan Area (MCMA), while older air masses show both thinly-coated and thickly-coated BC. Some 2-day-old plumes do not show a prominent thickly-coated BC mode, possibly due to preferential wet scavenging of the likely-hydrophilic thickly-coated BC.

The goal of this study was to test if Asian long-range transport (ALRT) of pollutants leads to enhanced levels of atmospheric mercury in the Colorado Rocky Mountains in the United States. Storm Peak Laboratory, a high-elevation (3200 m asl) mountaintop research facility, is located on top of the Continental Divide ideally exposed to the prevailing westerly winds 1500 km inland from the Pacific where near-coastal stations previously measured significant atmospheric mercury enhancements due to ALRT. Measurements of gaseous elemental mercury (GEM) from October 2006 to May 2007 averaged 1.51 � 0.12 ng m �3 at this laboratory, with minimum and maximum concentrations of 1.06 ng m �3 and 2.15 ng m �3 , respectively. GEM showed diel patterns with peak concentrations during daytime and lowest concentrations during late night and early morning hours. In fall and winter, these patterns closely followed diel fluctuations of water vapor, aerosol number concentration, and ozone. The patterns are hence attributed to transitions of daytime boundary layer and nighttime air masses with regional representation as daytime surface heating causes air masses enhanced with air pollutants to rise from the valley floor to the laboratory. In spring, diel patterns of GEM and carbon monoxide (CO) occurred time-shifted in respect to water vapor, aerosol number, and ozone concentrations, indicating additional or different sources or sinks. A large GEM enhancement (2.15 ng m

▪ Abstract Agriculture and industrial development have led to inadvertent changes in the natural carbon cycle. As a consequence, concentrations of carbon dioxide and other greenhouse gases have increased in the atmosphere and may lead to changes in climate. The current challenge facing society is to develop options for future management of the carbon cycle. A variety of approaches has been suggested: direct reduction of emissions, deliberate manipulation of the natural carbon cycle to enhance sequestration, and capture and isolation of carbon from fossil fuel use. Policy development to date has laid out some of the general principles to which carbon management should adhere. These are summarized as: how much carbon is stored, by what means, and for how long. To successfully manage carbon for climate purposes requires increased understanding of carbon cycle dynamics and improvement in the scientific capabilities available for measurement as well as for policy needs. The specific needs for scientific information to underpin carbon cycle management decisions are not yet broadly known. A stronger dialogue between decision makers and scientists must be developed to foster improved application of scientific knowledge to decisions. This review focuses on the current knowledge of the carbon cycle, carbon measurement capabilities (with an emphasis on the continental scale) and the relevance of carbon cycle science to carbon sequestration goals.

We measured soil respiration during two winters in three different ecotypes of the BOREAS northern study area. The production of CO2 was continuous throughout the winter and, when totaled for the winter of 1993-1995, was equivalent to the release of similar to 40-55 g C/m(2) from the soil surface. As soils cooled in the early winter, the CO2 production rate decreased in a manner that appeared to be exponentially related to shallow soil temperatures. This exponential relationship was not observed when soils began to warm, possibly indicating that there may be additional or different processes responsible for increased CO2 production during winter warming events. We also measured CO2 concentrations in soil gas and the Delta(14)C of the soil CO2. These measurements show that the CO2 produced in winter is not simply the return to the atmosphere Of the carbon fixed during the previous growing season. We suggest that the wintertime production of CO2 originates, at least in part, from the decomposition of old organic carbon stored at depth in the soil.

We have developed an instrument for making continuous, field-based, part-per-million (ppm) level measurements of atmospheric oxygen concentration, and have implemented it on research cruises in the equatorial Pacific and Southern Oceans. The instrument detects changes in oxygen by the absorption of vacuum ultraviolet (VUV) radiation as it passes through a flowing gas stream, and has a precision comparable to existing laboratory techniques. Here we describe the VUV instrument and present atmospheric O 2 and CO 2 data collected from the NOAA ship Ka'imimoana in the equatorial Pacific during April and May of 1998, and from the NSF ship Lawrence M. Gould in the Southern Ocean during October 1998. These data represent the first field-based measurements of atmospheric O 2 , and significant additions to the O 2 datasets in these regions. Our boreal-springtime equatorial measurements reveal significant short-term variations in atmospheric O 2 , resulting from variations in atmospheric mixing relative to the strong interhemispheric gradient. Our austral-springtime Southern Ocean observations confirm the low O 2 concentrations seen in flask samples from this region, allow the separate identification of oceanic and industrial influences on CO 2 , and provide evidence of a Southern Ocean source for CO 2 at this time of year. These shipboard VUV observations do not provide any evidence to support coupled ocean–atmosphere model predictions of a large decreasing atmospheric O 2 gradient between equatorial and high-southern latitudes. DOI: 10.1046/j.1435-6935.2003.00075.x

[1] High-elevation forests represent a large fraction of potential carbon uptake in North America, but this uptake is not well constrained by observations. Additionally, forests in the Rocky Mountains have recently been severely damaged by drought, fire, and insect outbreaks, which have been quantified at local scales but not assessed in terms of carbon uptake at regional scales. The Airborne Carbon in the Mountains Experiment was carried out in 2007 partly to assess carbon uptake in western U.S. mountain ecosystems. The magnitude and seasonal change of carbon uptake were quantified by (1) paired upwind-downwind airborne CO2 observations applied in a boundary layer budget, (2) a spatially explicit ecosystem model constrained using remote sensing and flux tower observations, and (3) a downscaled global tracer transport inversion. Top-down approaches had mean carbon uptake equivalent to flux tower observations at a subalpine forest, while the ecosystem model showed less. The techniques disagreed on temporal evolution. Regional carbon uptake was greatest in the early summer immediately following snowmelt and tended to lessen as the region experienced dry summer conditions. This reduction was more pronounced in the airborne budget and inversion than in flux tower or upscaling, possibly related to lower snow water availability in forests sampled by the aircraft, which were lower in elevation than the tower site. Changes in vegetative greenness associated with insect outbreaks were detected using satellite reflectance observations, but impacts on regional carbon cycling were unclear, highlighting the need to better quantify this emerging disturbance effect on montane forest carbon cycling.

[1] A multiple-box model was developed to determine how meteorological, anthropogenic, and biological processes combine to produce diel cycles of carbon dioxide (CO2) mole fraction during each of the four calendar-based seasons within Salt Lake Valley, Utah, USA. The model was forced by observed winds, sounding-derived mixing depths, an anthropogenic CO2 emissions inventory, and net biological flux estimates based on temperature, solar radiation, and ecosystem type. The model was validated using hourly CO2 mole fractions measured at five sites in the urban Salt Lake Valley (uSLV) area for 2005–2009 (spatial average of observations denoted by Cobs). The model accounted for 53% of Cobs on an hourly basis, and accounted for 90–94% of the mean diel cycle of Cobs depending on season. The multiple-box model results indicated that CO2 change rates within the uSLV mean diel cycles were largely the result of imbalances between anthropogenic processes adding CO2 and meteorological processes removing or diluting CO2. Removal by wind (advection) was the most important CO2 reduction process on average, but dilution of CO2 by entrainment of air from above the mixing height overtook advection in importance between sunrise and midday. During summer mornings, CO2 reduction attributable to photosynthesis below shallow mixing heights was of intermediate importance between advection and entrainment, but the overall net effect of biological processes was the least important influence on CO2 change rates during each of the four seasons.

Methane and nitrous oxide are potent greenhouse gases whose atmospheric abundances have increased significantly in the past 200 years, together accounting for approximately half of the radiative forcing associated with increasing concentrations of carbon dioxide. In order to understand the factors causing increase of these gases globally, we need to determine their emission rates at regional to continental scales. We directly link atmospheric observations with surface emissions using a Lagrangian Particle Dispersion Model, and then determine emission rates by optimizing prior emissions estimates. We use measurements from NOAA's tall tower and aircraft program in 2004, The Stochastic Time-Inverted Lagrangian Transport model (STILT) driven by meteorological fields from a customized version of the Weather Research and Forecasting (WRF) model, and EDGAR32FT2000 and Global Emissions Inventory Activity (GEIA) as prior emission estimates. In the US and Canada, methane emission rates are found to be consistent wi...

We present top-down emission constraints for two non-CO2 greenhouse gases in large areas of the U. S. and southern Canada during early summer. Collocated airborne measurements of methane and nitrous oxide acquired during the COBRA-NA campaign in May-June 2003, analyzed using a receptor-oriented Lagrangian particle dispersion model, provide robust validation of independent bottom-up emission estimates from the EDGAR and GEIA inventories. We find that the EDGAR CH4 emission rates are slightly low by a factor of 1.08 +/- 0.15 (2 sigma), while both EDGAR and GEIA N2O emissions are significantly too low, by factors of 2.62 +/- 0.50 and 3.05 +/- 0.61, respectively, for this region. Potential footprint bias may expand the statistically retrieved uncertainties. Seasonality of agricultural N2O emissions may help explain the discrepancy. Total anthropogenic U.S. and Canadian emissions would be 49 Tg CH4 and 4.3 Tg N2O annually, if these inventory scaling factors applied to all of North America. [References: 21]

Measurements of midday vertical atmospheric CO 2 distributions reveal annual-mean vertical CO 2 gradients that are inconsistent with atmospheric models that estimate a large transfer of terrestrial carbon from tropical to northern latitudes. The three models that most closely reproduce the observed annual-mean vertical CO 2 gradients estimate weaker northern uptake of –1.5 petagrams of carbon per year (Pg C year –1 ) and weaker tropical emission of +0.1 Pg C year –1 compared with previous consensus estimates of –2.4 and +1.8 Pg C year –1 , respectively. This suggests that northern terrestrial uptake of industrial CO 2 emissions plays a smaller role than previously thought and that, after subtracting land-use emissions, tropical ecosystems may currently be strong sinks for CO 2 .