New constraints of terrestrial and oceanic global gross primary productions from the triple oxygen isotopic composition of atmospheric CO2 and O2

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 O₂ and CO₂ 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 CO₂) and constrain, on an annual basis, the global CO₂ 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 CO₂ 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 intra-annual variability implies that the entire atmospheric CO₂ 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.

129I in rainwater across Argentina

Concentrations of ¹²⁷I and ¹²⁹I in rainwater samples from several stations across Argentina (latitudes between 25° S and 55° S) were measured and analyzed for the assessment of distribution patterns and potential sources of ¹²⁹I in the Southern Hemisphere. Measured ¹²⁹I levels, clearly above those explainable by natural background and atmospheric nuclear weapons tests, can be understood by the injection into the Southern Hemisphere of ¹²⁹I that had been discharged from nuclear fuel reprocessing plants in the Northern Hemisphere.

Half a century of Krypton-85 activity concentration measured in air over Central Europe: Trends and relevance for dating young groundwater

For almost half a century weekly samples for the measurement of krypton-85 (⁸⁵Kr) activity concentrations in surface air have been collected by the Bundesamt für Strahlenschutz (BfS), Germany. Sampling started at Freiburg (230m asl) in 1973, Mt Schauinsland (1205m asl) in 1976 and Mt Jungfraujoch in Switzerland (3454 asl) in 1990. Distinct maxima in the time series of atmospheric ⁸⁵Kr activity concentration are caused by emissions from nuclear reprocessing plants in Europe, mainly the La Hague, France, and Sellafield, UK, reprocessing plants. Between 1970 and 1990 peak activity concentrations measured in winter along the Rhine Rift in Freiburg are often higher than at Mt Schauinsland, due to emissions from the operating pilot reprocessing plant in Karlsruhe - approximately 130 km to the north - and large-scale inversions that inhibit exchange of air masses within the Rhine Rift with those at higher altitudes. From the early 1990s onwards, after the shut-down of the pilot plant, differences between Freiburg and Schauinsland are much smaller. Activity concentrations measured at Jungfraujoch are generally lower and close to baseline levels, due to its location in the free troposphere. Weekly baseline and average ⁸⁵Kr activity concentration in the atmosphere in Central Europe were modelled from almost 12,000 individual measurements at 11 stations. The baseline and average have continuously increased, interrupted by a relatively stable period between 2009 and the end of 2014 with a baseline activity concentration of about 1.39 Bq/m³. Depending on the geographical location and hydrological conditions, the modelled baseline or average ⁸⁵Kr activity concentration time series can be used as input functions for the dating of young groundwater.

Oxygen isotope anomaly in tropospheric CO2 and implications for CO2 residence time in the atmosphere and gross primary productivity

The abundance variations of near surface atmospheric CO₂ isotopologues (primarily ¹⁶O¹²C¹⁶O, ¹⁶O¹³C¹⁶O, ¹⁷O¹²C¹⁶O, and ¹⁸O¹²C¹⁶O) represent an integrated signal from anthropogenic/biogeochemical processes, including fossil fuel burning, biospheric photosynthesis and respiration, hydrospheric isotope exchange with water, and stratospheric photochemistry. Oxygen isotopes, in particular, are affected by the carbon and water cycles. Being a useful tracer that directly probes governing processes in CO₂ biogeochemical cycles, Δ¹⁷O (=ln(1 + δ¹⁷O) - 0.516 × ln(1 + δ¹⁸O)) provides an alternative constraint on the strengths of the associated cycles involving CO₂. Here, we analyze Δ¹⁷O data from four places (Taipei, Taiwan; South China Sea; La Jolla, United States; Jerusalem, Israel) in the northern hemisphere (with a total of 455 measurements) and find a rather narrow range (0.326 ± 0.005‰). A conservative estimate places a lower limit of 345 ± 70 PgC year^-1 on the cycling flux between the terrestrial biosphere and atmosphere and infers a residence time of CO₂ of 1.9 ± 0.3 years (upper limit) in the atmosphere. A Monte Carlo simulation that takes various plant uptake scenarios into account yields a terrestrial gross primary productivity of 120 ± 30 PgC year^-1 and soil invasion of 110 ± 30 PgC year^-1, providing a quantitative assessment utilizing the oxygen isotope anomaly for quantifying CO₂ cycling.

Extending the Community Multiscale Air Quality (CMAQ) Modeling System to Hemispheric Scales: Overview of Process Considerations and Initial Applications

The Community Multiscale Air Quality (CMAQ) modeling system is extended to simulate ozone, particulate matter, and related precursor distributions throughout the Northern Hemisphere. Modelled processes were examined and enhanced to suitably represent the extended space and time scales for such applications. Hemispheric scale simulations with CMAQ and the Weather Research and Forecasting (WRF) model are performed for multiple years. Model capabilities for a range of applications including episodic long-range pollutant transport, long-term trends in air pollution across the Northern Hemisphere, and air pollution-climate interactions are evaluated through detailed comparison with available surface, aloft, and remotely sensed observations. The expansion of CMAQ to simulate the hemispheric scales provides a framework to examine interactions between atmospheric processes occurring at various spatial and temporal scales with physical, chemical, and dynamical consistency.

Observational evidence for interhemispheric hydroxyl-radical parity

The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere. 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 methane. It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4, 7-10). 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 campaigns. 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.

Fukushima's forgotten radionuclides: a review of the understudied radioactive emissions

In environmental monitoring campaigns for anthropogenic radionuclides released in the course of the Fukushima nuclear accident (2011), most focus had been on gamma-emitting radionuclides. More than 99% of the released activity was due to radionuclides of the elements Kr, Te, I, Xe, and Cs. However, little work had been done on the monitoring of radionuclides other than (131)I, (132)Te, (134)Cs, (136)Cs, and (137)Cs. Radionuclides such as those of less volatile elements (e.g., (89)Sr, (90)Sr, (103)Ru, (106)Ru, plutonium), pure beta-emitters ((3)H, (14)C, (35)S), gaseous radionuclides ((85)Kr, (133)Xe, (135)Xe) or radionuclides with very long half-lives (e.g., (36)Cl, (99)Tc, (129)I, some actinides such as (236)U) have been understudied by comparison. In this review, we summarize previous monitoring work on these "orphan" radionuclides in various environmental media and outline further challenges for future monitoring campaigns. Some of the understudied radionuclides are of radiological concern, others are promising tracers for environmental, geochemical processes such as oceanic mixing. Unfortunately, the shorter-lived nuclides of radioxenon, (103)Ru, (89)Sr and (35)S will no longer exhibit detectable activities in the environment. Activity concentrations of other radionuclides such as tritium, (14)C, or (85)Kr will become blurred in the significant background of previous releases (nuclear explosions and previous accidents). Isotope ratios such as (240)Pu/(239)Pu will allow for the identification of Fukushima plutonium despite the plutonium background.

Analysis of 85Kr: a comparison at the 10 -14 level using micro-liter samples

The isotopic abundance of (85)Kr in the atmosphere, currently at the level of 10(-11), has increased by orders of magnitude since the dawn of nuclear age. With a half-life of 10.76 years, (85)Kr is of great interest as tracers for environmental samples such as air, groundwater and ice. Atom Trap Trace Analysis (ATTA) is an emerging method for the analysis of rare krypton isotopes at isotopic abundance levels as low as 10(-14) using krypton gas samples of a few micro-liters. Both the reliability and reproducibility of the method are examined in the present study by an inter-comparison among different instruments. The (85)Kr/Kr ratios of 12 samples, in the range of 10(-13) to 10(-10), are measured independently in three laboratories: a low-level counting laboratory in Bern, Switzerland, and two ATTA laboratories, one in Hefei, China, and another in Argonne, USA. The results are in agreement at the precision level of 5%.

Global source-receptor relationships for mercury deposition under present-day and 2050 emissions scenarios

Global policies regulating anthropogenic mercury require an understanding of the relationship between emitted and deposited mercury on intercontinental scales. Here, we examine source-receptor relationships for present-day conditions and four 2050 IPCC scenarios encompassing a range of economic development and environmental regulation projections. We use the GEOS-Chem global model to track mercury from its point of emission through rapid cycling in surface ocean and land reservoirs to its accumulation in longer lived ocean and soil pools. Deposited mercury has a local component (emitted Hg(II), lifetime of 3.7 days against deposition) and a global component (emitted Hg(0), lifetime of 6 months against deposition). Fast recycling of deposited mercury through photoreduction of Hg(II) and re-emission of Hg(0) from surface reservoirs (ice, land, surface ocean) increases the effective lifetime of anthropogenic mercury to 9 months against loss to legacy reservoirs (soil pools and the subsurface ocean). This lifetime is still sufficiently short that source-receptor relationships have a strong hemispheric signature. Asian emissions are the largest source of anthropogenic deposition to all ocean basins, though there is also regional source influence from upwind continents. Current anthropogenic emissions account for only about one-third of mercury deposition to the global ocean with the remainder from natural and legacy sources. However, controls on anthropogenic emissions would have the added benefit of reducing the legacy mercury re-emitted to the atmosphere. Better understanding is needed of the time scales for transfer of mercury from active pools to stable geochemical reservoirs.

The atmospheric signature of carbon capture and storage

Compared with other industrial processes, carbon capture and storage (CCS) will have an unusual impact on atmospheric composition by reducing the CO(2) released from fossil-fuel combustion plants, but not reducing the associated O(2) loss. CO(2) that leaks into the air from below-ground CCS sites will also be unusual in lacking the O(2) deficit normally associated with typical land CO(2) sources, such as from combustion or ecosystem exchanges. CCS may also produce distinct isotopic changes in atmospheric CO(2). Using simple models and calculations, we estimate the impact of CCS or leakage on regional atmospheric composition. We also estimate the possible impact on global atmospheric composition, assuming that the technology is widely adopted. Because of its unique signature, CCS may be especially amenable to monitoring, both regionally and globally, using atmospheric observing systems. Measurements of the O(2)/N(2) ratio and the CO(2) concentration in the proximity of a CCS site may allow detection of point leaks of the order of 1000 ton CO(2) yr(-1) from a CCS reservoir up to 1 km from the source. Measurements of O(2)/N(2) and CO(2) in background air from a global network may allow quantification of global and hemispheric capture rates from CCS to the order of ±0.4 Pg C yr(-1).

Quantifying remoteness from emission sources of persistent organic pollutants on a global scale

One of the four screening criteria that are assessed when a chemical substance is nominated for international regulation under the Stockholm Convention is potential for long-range transport. Measured levels of a chemical in locations distant from sources can be used as evidence of long-range environmental transport, but until now, there has been no quantitative measure of the distance of a location from likely source areas of chemicals. Here we use a global atmospheric transport model to calculate atmospheric concentrations for a set of volatile tracers that differ in their effective atmospheric residence time. We then derive an empirical relationship to express these concentrations as a function of the atmospheric residence time and a location-specific parameter, the remoteness index, RI. We present maps of RI for two generic emissions scenarios that represent areas for emissions of industrial and technical chemicals and pesticides, respectively. Our results can be used to better interpret spatial patterns of measured and modeled concentrations of chemicals in the global environment and to derive long-range transport potential metrics for specific substances. We thus provide, to our knowledge for the first time, a description of remoteness that is applicable to measurement sites of continental- and global-scale monitoring programmes. Our results can be used to plan future measurement campaigns and extend monitoring networks.

A new compilation of the atmospheric 85krypton inventories from 1945 to 2000 and its evaluation in a global transport model

This paper gives the yearly (85)Kr emissions of all known reprocessing facilities, which are the main sources of (85)Kr in the atmosphere since 1945, for the years 1945 until 2000. According to this inventory 10,600 PBq (Peta=10(15)) of (85)Kr have been globally emitted from the year 1945 until the end of 2000. The global atmospheric inventory at the end of the year 2000 amounts to 4800 PBq. These emissions have been incorporated into the ECHAM4 atmospheric general circulation model as point sources. Monthly mean model results are compared with measurements made at different locations and times. The influence of each source on the measured concentrations at various locations is studied. The calculated concentrations are found to give reasonably good agreement with the observations, indicating that the emission inventory is realistic. Although, at all northern hemispheric observation sites the model tends to slightly overestimate the concentrations. A possible reason for this overestimation can be found in model features (coarse resolution in time and space). The most prominent discrepancy that is consistently repeated at all northern hemispheric stations occurs in the early 1990s. This could most likely be related to an overestimate of sources. Possibly, the Russian emissions declined earlier than assumed in the current database. Another discrepancy between observations and simulations indicating an incompleteness of the release data is found at some southern hemispheric sites. The variability of their observations could only be explained by regional sources. However, several spikes occur after 1992 when no reprocessing facility is known to be in operation in the southern hemisphere. Production of isotopes for radiopharmaceuticals like technetium-99m from highly enriched uranium is the most likely explanation.

The distribution of the chlorinated solvents dichloromethane, perchloroethylene, and trichloroethylene in the global atmosphere

Dichloromethane, perchloroethylene, and trichloroethylene are commercially important chlorinated solvents whose health and environmental impacts are under scrutiny in the industrial world. Their distributions in the global atmosphere have been computed based on data from the Reactive Chlorine Emissions Inventory (RCEI) project using the Global Balance Environment (GLOBE) model, a 3-D radiative-dynamical-chemical model. Their atmospheric lifetimes, scaled to an observed methyl chloroform lifetime of 4.8 years, are 158 days, 105 days, and 4.3 days, respectively. They have strong interhemispheric gradients, with maximum zonal mean surface concentrations in the winter mid-latitude northern hemisphere of approximately 40 ppt, 9 ppt, and 2.5 ppt, respectively. Their spatial distributions show significant seasonal variability, and are sensitive to vertical mixing by cumulus convection and horizontal mixing by synoptic-scale turbulence. While the model interhemispheric exchange time (1.0 years) and computed atmospheric lifetimes are very sensitive to sub-grid scale diffusion, interhemispheric gradients of the chlorinated solvents are not. The simulated results suggest a greater importance for oceanic emissions of perchloroethylene and trichloroethylene than has previously been assumed.