Measurements Of CO2 Mixing Ratios Research Articles

Anthropogenic Methane Emission and Its Partitioning for the Yangtze River Delta Region of China

AbstractUrban areas are global methane (CH4) hotspots. Yet large uncertainties still remain for the CH4 budget of these domains. The Yangtze River Delta (YRD), China, is one of the world's most densely populated regions where a large number of cities are located. To estimate anthropogenic CH4 emissions in YRD, we conducted simultaneous atmospheric CH4 and CO2 mixing ratio measurements from June 2010 to April 2011. By combining these measurements with the Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport models and a priori Emission Database for Global Atmospheric Research emission inventories, we applied three “top‐down” approaches to constrain anthropogenic CH4 emissions. These three approaches included multiplicative scaling factors, flux ratio, and scale factor Bayesian inversion. The posteriori CH4 flux density estimated from the three approaches showed high consistency and were 36.32 (±9.17), 35.66 (±2.92), and 36.03(±14.25) nmol·m−2·s−1, respectively, for the duration of the study period (November 2010 to April 2011). The total annual anthropogenic CH4 emission was 6.52(±1.59) Tg for the YRD region based on the average of these three approaches. Our emission estimates were 30.2(±17.6)%, 31.5 (±5.6)%, and 30.8 (±27.4)% lower than the a priori Emission Database for Global Atmospheric Research v432 emission inventory estimate. The scale factor Bayesian inversion results indicate that the overestimate was mainly caused by two source categories including fuel exploitation and agricultural soil emissions (rice cultivation). The posteriori flux densities for agricultural soil and fuel exploitation were 10.68 and 6.34 nmol·m−2·s−1, respectively, and were 47.8% and 29.2% lower than the a priori inventory. Agricultural soil was the largest source contribution and accounted for 29.6% of the YRD CH4 budget during the study period.

Anthropogenic CO2 emissions from a megacity in the Yangtze River Delta of China.

Anthropogenic CO2 emissions from cities represent a major source contributing to the global atmospheric CO2 burden. Here, we examined the enhancement of atmospheric CO2 mixing ratios by anthropogenic emissions within the Yangtze River Delta (YRD), China, one of the world's most densely populated regions (population greater than 150 million). Tower measurements of CO2 mixing ratios were conducted from March 2013 to August 2015 and were combined with numerical source footprint modeling to help constrain the anthropogenic CO2 emissions. We simulated the CO2 enhancements (i.e., fluctuations superimposed on background values) for winter season (December, January, and February). Overall, we observed mean diurnal variation of CO2 enhancement of 23.5~49.7μmolmol-1, 21.4~52.4μmolmol-1, 28.1~55.4μmolmol-1, and 29.5~42.4μmolmol-1 in spring, summer, autumn, and winter, respectively. These enhancements were much larger than previously reported values for other countries. The diurnal CO2 enhancements reported here showed strong similarity for all 3years of the study. Results from source footprint modeling indicated that our tower observations adequately represent emissions from the broader YRD area. Here, the east of Anhui and the west of Jiangsu province contributed significantly more to the anthropogenic CO2 enhancement compared to the other sectors of YRD. The average anthropogenic CO2 emission in 2014 was 0.162 (± 0.005) mgm-2s-1 and was 7 ± 3% higher than 2010 for the YRD. Overall, our emission estimates were significantly smaller (9.5%) than those estimated (0.179mgm-2s-1) from the EDGAR emission database.

Potential of European <sup>14</sup>CO<sub>2</sub> observation network to estimate the fossil fuel CO<sub>2</sub> emissions via atmospheric inversions

Abstract. Combining measurements of atmospheric CO2 and its radiocarbon (14CO2) fraction and transport modeling in atmospheric inversions offers a way to derive improved estimates of CO2 emitted from fossil fuel (FFCO2). In this study, we solve for the monthly FFCO2 emission budgets at regional scale (i.e., the size of a medium-sized country in Europe) and investigate the performance of different observation networks and sampling strategies across Europe. The inversion system is built on the LMDZv4 global transport model at 3.75∘ × 2.5∘ resolution. We conduct Observing System Simulation Experiments (OSSEs) and use two types of diagnostics to assess the potential of the observation and inverse modeling frameworks. The first one relies on the theoretical computation of the uncertainty in the estimate of emissions from the inversion, known as “posterior uncertainty”, and on the uncertainty reduction compared to the uncertainty in the inventories of these emissions, which are used as a prior knowledge by the inversion (called “prior uncertainty”). The second one is based on comparisons of prior and posterior estimates of the emission to synthetic “true” emissions when these true emissions are used beforehand to generate the synthetic fossil fuel CO2 mixing ratio measurements that are assimilated in the inversion. With 17 stations currently measuring 14CO2 across Europe using 2-week integrated sampling, the uncertainty reduction for monthly FFCO2 emissions in a country where the network is rather dense like Germany, is larger than 30 %. With the 43 14CO2 measurement stations planned in Europe, the uncertainty reduction for monthly FFCO2 emissions is increased for the UK, France, Italy, eastern Europe and the Balkans, depending on the configuration of prior uncertainty. Further increasing the number of stations or the sampling frequency improves the uncertainty reduction (up to 40 to 70 %) in high emitting regions, but the performance of the inversion remains limited over low-emitting regions, even assuming a dense observation network covering the whole of Europe. This study also shows that both the theoretical uncertainty reduction (and resulting posterior uncertainty) from the inversion and the posterior estimate of emissions itself, for a given prior and “true” estimate of the emissions, are highly sensitive to the choice between two configurations of the prior uncertainty derived from the general estimate by inventory compilers or computations on existing inventories. In particular, when the configuration of the prior uncertainty statistics in the inversion system does not match the difference between these prior and true estimates, the posterior estimate of emissions deviates significantly from the truth. This highlights the difficulty of filtering the targeted signal in the model–data misfit for this specific inversion framework, the need to strongly rely on the prior uncertainty characterization for this and, consequently, the need for improved estimates of the uncertainties in current emission inventories for real applications with actual data. We apply the posterior uncertainty in annual emissions to the problem of detecting a trend of FFCO2, showing that increasing the monitoring period (e.g., more than 20 years) is more efficient than reducing uncertainty in annual emissions by adding stations. The coarse spatial resolution of the atmospheric transport model used in this OSSE (typical of models used for global inversions of natural CO2 fluxes) leads to large representation errors (related to the inability of the transport model to capture the spatial variability of the actual fluxes and mixing ratios at subgrid scales), which is a key limitation of our OSSE setup to improve the accuracy of the monitoring of FFCO2 emissions in European regions. Using a high-resolution transport model should improve the potential to retrieve FFCO2 emissions, and this needs to be investigated.

Space-based active optical remote sensing of carbon dioxide column using high-energy two-micron pulsed ipda lidar

Modeling of a space-based high-energy 2-μm triple-pulse Integrated Path Differential Absorption (IPDA) lidar was conducted to demonstrate carbon dioxide (CO2) measurement capability and to evaluate random and systematic errors. A high pulse energy laser and an advanced MCT e-APD detector were incorporated in this model. Projected performance shows 0.5 ppm precision and 0.3 ppm bias in low-tropospheric column CO2 mixing ratio measurements from space for 10 second signal averaging over Railroad Valley (RRV) reference surface.

A mobile sensor network to map carbon dioxide emissions in urban environments

Abstract. A method for directly measuring carbon dioxide (CO2) emissions using a mobile sensor network in cities at fine spatial resolution was developed and tested. First, a compact, mobile system was built using an infrared gas analyzer combined with open-source hardware to control, georeference, and log measurements of CO2 mixing ratios on vehicles (car, bicycles). Second, two measurement campaigns, one in summer and one in winter (heating season) were carried out. Five mobile sensors were deployed within a 1 × 12. 7 km transect across the city of Vancouver, BC, Canada. The sensors were operated for 3.5 h on pre-defined routes to map CO2 mixing ratios at street level, which were then averaged to 100 × 100 m grid cells. The averaged CO2 mixing ratios of all grids in the study area were 417.9 ppm in summer and 442.5 ppm in winter. In both campaigns, mixing ratios were highest in the grid cells of the downtown core and along arterial roads and lowest in parks and well vegetated residential areas. Third, an aerodynamic resistance approach to calculating emissions was used to derive CO2 emissions from the gridded CO2 mixing ratio measurements in conjunction with mixing ratios and fluxes collected from a 28 m tall eddy-covariance tower located within the study area. These measured emissions showed a range of −12 to 226 CO2 ha−1 h−1 in summer and of −14 to 163 kg CO2 ha−1 h−1 in winter, with an average of 35.1 kg CO2 ha−1 h−1 (summer) and 25.9 kg CO2 ha−1 h−1 (winter). Fourth, an independent emissions inventory was developed for the study area using buildings energy simulations from a previous study and routinely available traffic counts. The emissions inventory for the same area averaged to 22.06 kg CO2 ha−1 h−1 (summer) and 28.76 kg CO2 ha−1 h−1 (winter) and was used to compare against the measured emissions from the mobile sensor network. The comparison on a grid-by-grid basis showed linearity between CO2 mixing ratios and the emissions inventory (R2 = 0. 53 in summer and R2 = 0. 47 in winter). Also, 87 % (summer) and 94 % (winter) of measured grid cells show a difference within ±1 order of magnitude, and 49 % (summer) and 69 % (winter) show an error of less than a factor 2. Although associated with considerable errors at the individual grid cell level, the study demonstrates a promising method of using a network of mobile sensors and an aerodynamic resistance approach to rapidly map greenhouse gases at high spatial resolution across cities. The method could be improved by longer measurements and a refined calculation of the aerodynamic resistance.

CO2 surface fluxes at grid point scale estimated from a global 21 year reanalysis of atmospheric measurements

This paper documents a global Bayesian variational inversion of CO2 surface fluxes during the period 1988–2008. Weekly fluxes are estimated on a 3.75° × 2.5° (longitude‐latitude) grid throughout the 21 years. The assimilated observations include 128 station records from three large data sets of surface CO2 mixing ratio measurements. A Monte Carlo approach rigorously quantifies the theoretical uncertainty of the inverted fluxes at various space and time scales, which is particularly important for proper interpretation of the inverted fluxes. Fluxes are evaluated indirectly against two independent CO2 vertical profile data sets constructed from aircraft measurements in the boundary layer and in the free troposphere. The skill of the inversion is evaluated by the improvement brought over a simple benchmark flux estimation based on the observed atmospheric growth rate. Our error analysis indicates that the carbon budget from the inversion should be more accurate than the a priori carbon budget by 20% to 60% for terrestrial fluxes aggregated at the scale of subcontinental regions in the Northern Hemisphere and over a year, but the inversion cannot clearly distinguish between the regional carbon budgets within a continent. On the basis of the independent observations, the inversion is seen to improve the fluxes compared to the benchmark: the atmospheric simulation of CO2 with the Bayesian inversion method is better by about 1 ppm than the benchmark in the free troposphere, despite possible systematic transport errors. The inversion achieves this improvement by changing the regional fluxes over land at the seasonal and at the interannual time scales.

Ultrasonic Detector for High Precision Measurements of Carbon Dioxide

A new instrument for monitoring atmospheric CO(2) has been developed based on the measurement of the speed of sound in air. The instrument uses a selective scrubber to yield highly precise and accurate measurements of CO(2) mixing ratios at ambient concentrations. The instrument has a precision of 0.3 ppmv (1σ) with a signal that is independent of pressure and requires a flow rate of only 30 mL/min. Laboratory measurements of atmospheric CO(2) showed excellent agreement with values obtained by nondispersive infrared absorption. The instrument has the advantage of collecting continuous, high-precision data every 25 s and can be modified for vertical profiling studies using kites, balloons, or light aircraft for the purpose of measuring landscape-scale fluxes.

Atmospheric Fossil Fuel CO2 Measurement Using a Field Unit in a Central European City During the Winter of 2008/09

A high-precision atmospheric CO2 monitoring station was developed as a field unit. Within this, an integrating CO2 sampling system was applied to collect samples for radiocarbon measurements. One sampler was installed in the second largest city of Hungary (Debrecen station) and 2 independent 14CO2 sampling lines were installed ∼300 km from Debrecen in a rural site at Hegyhátsál station as independent background references, where high-precision atmospheric CO2 mixing ratios have been measured since 1994. Fossil fuel CO2 content in the air of the large Hungarian city of Debrecen was determined during the winter of 2008 using both the measurements of CO2 mixing ratio and 14C content of air. Fossil fuel CO2 was significantly enhanced at Debrecen relative to the clean-air site at Hegyhátsál.

Vertical 2-μm Heterodyne Differential Absorption Lidar Measurements of Mean CO2 Mixing Ratio in the Troposphere

Abstract Vertical mean CO2 mixing ratio measurements are reported in the atmospheric boundary layer (ABL) and in the lower free troposphere (FT), using a 2-μm heterodyne differential absorption lidar (HDIAL). The mean CO2 mixing ratio in the ABL is determined using 1) aerosol backscatter signal and a mean derivative of the increasing optical depth as a function of altitude and 2) optical depth measurements from cloud target returns. For a 1-km vertical long path in the ABL, 2% measurement precision with a time resolution of 30 min is demonstrated for the retrieved mean CO2 absorption. Spectroscopic calculations are reported in details using new spectroscopic data in the 2-μm domain and the outputs of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). Then, using both aerosols in the ABL and midaltitude dense clouds in the free troposphere, preliminary HDIAL measurements of mean CO2 mixing ratio in the free troposphere are also presented. The 2-μm HDIAL vertical measurements are compared to ground-based and airborne in situ CO2 mixing ratio measurements and discussed with the atmospheric synoptic conditions.

New constraints on Northern Hemisphere growing season net flux

Observations of the column‐averaged dry molar mixing ratio of CO2 above both Park Falls, Wisconsin and Kitt Peak, Arizona, together with partial columns derived from aircraft profiles over Eurasia and North America are used to estimate the seasonal integral of net ecosystem exchange (NEE) between the atmosphere and the terrestrial biosphere in the Northern Hemisphere. We find that NEE is ∼25% larger than predicted by the Carnegie Ames Stanford Approach (CASA) model. We show that the estimates of NEE may have been biased low by too weak vertical mixing in the transport models used to infer seasonal changes in Northern Hemisphere CO2 mass from the surface measurements of CO2 mixing ratio.

Estimating daytime CO2 fluxes over a mixed forest from tall tower mixing ratio measurements

Difficulties in estimating terrestrial ecosystem CO2 fluxes on regional scales have significantly limited our understanding of the global carbon cycle. This paper presents an effort to estimate daytime CO2 fluxes over a forested region on the scale of 50 km in northern Wisconsin, USA, using the tall‐tower‐based mixed layer (ML) budget method. Budget calculations were conducted for 2 years under fair‐weather conditions as a case study. With long‐term measurements of CO2 mixing ratio at a 447‐m‐tall tower, daytime regional CO2 fluxes were estimated on the seasonal scale, longer than in earlier studies. The flux derived from the budget method was intermediate among those derived from the eddy‐covariance (EC) method at three towers in the region and overall closest to that derived from EC measurements at 396 m of the tall tower. The dormant season average daytime‐integrated regional CO2 flux was about 0.35 ± 0.18 gC m−2. During the growing season, the monthly averaged daytime‐integrated regional CO2 flux varied from −1.58 ± 0.19 to −4.15 ± 0.32 gC m−2, suggesting that the region was a net sink of CO2 in the daytime. We also discussed the effects on theses estimates of neglecting horizontal advection, selecting for fair‐weather conditions, and using single‐location measurements. Daytime regional CO2 flux estimates from the ML budget method were comparable to those from three aggregation experiments. Differences in results from the different methods, however, suggest that more constraints are needed to estimate regional fluxes with more confidence. Despite uncertainties, our analyses indicate that it is feasible to estimate daytime regional CO2 fluxes on long timescales using tall tower measurements.

Wavelength modulated off-axis integrated cavity output spectroscopy in the near infrared

A novel instrument based on an improved off-axis alignment of integrated cavity output spectroscopy (OA-ICOS) in conjunction with a wavelength modulation (WM) technique, was developed using a DFB diode laser operating in the near infrared at 1.573 μm (6357.3 cm-1). The laser-based sensor employed a 44 cm optical cavity that provided an effective absorption path length of ∼68 m. A minimum detectable absorption of approximately 3.6 ppmv Hz-1/2 or 2.3×10-7 Hz-1/2 per optical pass was obtained using second harmonic detection. We demonstrated that by implementation of the WM technique to OA-ICOS in the near infrared, the detection sensitivity was improved by a factor of 14 compared to that obtained with OA-ICOS. Measurements of CO2 mixing ratios in ambient air have been performed by using both OA-ICOS and WM-OA-ICOS techniques for performance comparison.

Regional carbon dioxide fluxes from mixing ratio data

We examine the atmospheric budget of CO2 at temperate continental sites in the Northern Hemisphere. On a monthly time scale both surface exchange and atmospheric transport are important in determining the rate of change of CO2 mixing ratio at these sites. Vertical differences between the atmospheric boundary layer and free troposphere over the continent are generally greater than large-scale zonal gradients such as the difference between the free troposphere over the continent and the marine boundary layer. Therefore, as a first approximation we parametrize atmospheric transport as a vertical exchange term related to the vertical gradient of CO2 and the mean vertical velocity from the NCEP Reanalysis model. Horizontal advection is assumed to be negligible in our simple analysis. We then calculate the net surface exchange of CO2 from CO2 mixing ratio measurements at four tower sites. The results provide estimates of the surface exchange that are representative of a regional scale (i.e. ⊼106 km2). Comparison with direct, local-scale (eddy covariance) measurements of net exchange with the ecosystems around the towers are reasonable after accounting for anthropogenic CO2 emissions within the larger area represented by the mixing ratio data. A network of tower sites and frequent aircraft vertical profiles, separated by several hundred kilometres, where CO2 is accurately measured would provide data to estimate horizontal and vertical advection and hence provide a means to derive net CO2 fluxes on a regional scale. At present CO2 mixing ratios are measured with sufficient accuracy relative to global reference gas standards at only a few continental sites. The results also confirm that flux measurements from carefully sited towers capture seasonal variations representative of large regions, and that the midday CO2 mixing ratios sampled in the atmospheric surface layer similarly capture regional and seasonal variability in the continental CO2 budget.

Aircraft Observation of CO2, CO2 O3 and H2 over the North Pacific during the PACE-7 Campaign

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO2 in the free troposphere between 5 and 11 km. Continuous measurements of CO2mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O3, were also observed using continuous measuring systems at the same time. CO2 over the northern Pacific (35¼N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO2 was quite similar to that of CO, but the relationship between CO2 and O3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO2variation. On the other hand, the CO2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO2 distributions over the western Pacific. Very low mixing ratios of O3 of less than 20 ppb were distributed in the latitude band of 15–30¼N at 11 km, reflecting the effects of transport from the equatorial region.

The annual cycles of CO2 and H2O exchange over a northern mixed forest as observed from a very tall tower

AbstractWe present the annual patterns of net ecosystem‐atmosphere exchange (NEE) of CO2 and H2O observed from a 447 m tall tower sited within a mixed forest in northern Wisconsin, USA. The methodology for determining NEE from eddy‐covariance flux measurements at 30, 122 and 396 m above the ground, and from CO2 mixing ratio measurements at 11, 30, 76, 122, 244 and 396 m is described. The annual cycle of CO2 mixing ratio in the atmospheric boundary layer (ABL) is also discussed, and the influences of local NEE and large‐scale advection are estimated. During 1997 gross ecosystem productivity (947−18 g C m−2 yr−1), approximately balanced total ecosystem respiration (963±19 g C m−2 yr−1), and NEE of CO2 was close to zero (16±19 g C m−2 yr−1 emitted into the atmosphere). The error bars represent the standard error of the cumulative daily NEE values. Systematic errors are also assessed. The identified systematic uncertainties in NEE of CO2 are less than 60 g C m−2 yr−1. The seasonal pattern of NEE of CO2 was highly correlated with leaf‐out and leaf‐fall, and soil thaw and freeze, and was similar to purely deciduous forest sites. The mean daily NEE of CO2 during the growing season (June through August) was −1.3 g C m−2 day−1, smaller than has been reported for other deciduous forest sites. NEE of water vapor largely followed the seasonal pattern of NEE of CO2, with a lag in the spring when water vapor fluxes increased before CO2 uptake. In general, the Bowen ratios were high during the dormant seasons and low during the growing season. Evapotranspiration normalized by potential evapotranspiration showed the opposite pattern. The seasonal course of the CO2 mixing ratio in the ABL at the tower led the seasonal pattern of NEE of CO2 in time: in spring, CO2 mixing ratios began to decrease prior to the onset of daily net uptake of CO2 by the forest, and in fall mixing ratios began to increase before the forest became a net source for CO2 to the atmosphere. Transport as well as local NEE of CO2 are shown to be important components of the ABL CO2 budget at all times of the year.

Strategies for measurement of atmospheric column means of carbon dioxide from aircraft using discrete sampling

Automated flask sampling aboard small charter aircraft has been proposed as a low‐cost, reliable method to greatly increase the density of measurements of CO2 mixing ratios in continental regions in order to provide data for assessment of global and regional CO2 budgets. We use data from the CO2 Budget and Rectification‐Airborne 2000 campaign over North America to study the feasibility of using discrete (flask) sampling to determine column mean CO2 in the lowest 4 km of the atmosphere. To simulate flask sampling, data were selected from profiles of CO2 measured continuously with an onboard (in situ) analyzer. We find that midday column means can be determined without bias relative to true column means measured by the in situ analyzer to within 0.15 and better than 0.10 ppm by using 10 and 20 instantaneously collected flask samples, respectively. More precise results can be obtained by using a flask sampling strategy that linearly integrates over portions of the air column. Using less than 8–10 flasks can lead to significant sampling bias for some common profile shapes. Sampling prior to the breakup of the nocturnal stable layer will generally lead to large sampling bias because of the inability of aircraft to probe large CO2 gradients that often exist very close to the ground at night and during the early morning.

Seasonal variability of greenhouse gases in the lower troposphere above the eastern European taiga (Syktyvkar, Russia)

A three year long record of regular vertical aircraft profiling for continuous atmospheric CO2 mixing ratio measurements as well as for flask sampling to derive the climatology of other greenhouse gases (CH4, SF6 and N2O), is presented. Measurements were undertaken in the lower troposphere between 100 and 3000 m over the eastern European taiga about 100 km south east of the city of Syktyvkar(61°24′N, 52°18′E). From the continuous profiles mean CO2 mixing ratios were calculated for the atmospheric boundary layer (ABL) and for the “free troposphere” up to 3000 m. The amplitudes of the respective seasonal cycles are 22.1 ± 3.5 and 14.0 ± 2.1 ppm. ABL mixing ratios are generally larger than free tropospheric values during the winter period, and smaller during the summer due to the change of the continental biosphere from a source to a sink. The phasing of the seasonal cycles is slightly different between the two height intervals (by about 30 days), with the ABL extremes occurring earlier. Very abrupt concentration changes up to 8 ppm are observed in the free troposphere associated with changes in air mass origin. Mean CO2 mixing ratios derived from flask samples at 3000 m compare well with the respective integrated values measured in the continuous profiles above the ABL (ΔCO2 = 0.3 ± 1.6 ppm). CH4 mixing ratios also show a pronounced seasonality, and winter time vertical gradients correlate well with those of CO2. Similarly, SF6 vertical gradients are correlated with CO2 gradients possibly pointing to some anthropogenic origin of the boundary layer CO2 signal during winter. N2O and SF6 also show a slight seasonality with almost the same phasing. The main reasons for the seasonality of both gases are probably transport processes with a possible contribution from stratosphere/troposphere exchange.

Seasonal variability of greenhouse gases in the lower troposphere above the eastern European taiga (Syktyvkar, Russia)

A three year long record of regular vertical aircraft profiling for continuous atmospheric CO2 mixing ratio measurements as well as for flask sampling to derive the climatology of other greenhouse gases (CH4, SF6 and N2O), is presented. Measurements were undertaken in the lower troposphere between 100 and 3000 m over the eastern European taiga about 100 km south east of the city of Syktyvkar(61°24′N, 52°18′E). From the continuous profiles mean CO2 mixing ratios were calculated for the atmospheric boundary layer (ABL) and for the “free troposphere” up to 3000 m. The amplitudes of the respective seasonal cycles are 22.1 ± 3.5 and 14.0 ± 2.1 ppm. ABL mixing ratios are generally larger than free tropospheric values during the winter period, and smaller during the summer due to the change of the continental biosphere from a source to a sink. The phasing of the seasonal cycles is slightly different between the two height intervals (by about 30 days), with the ABL extremes occurring earlier. Very abrupt concentration changes up to 8 ppm are observed in the free troposphere associated with changes in air mass origin. Mean CO2 mixing ratios derived from flask samples at 3000 m compare well with the respective integrated values measured in the continuous profiles above the ABL (ΔCO2 = 0.3 ± 1.6 ppm). CH4 mixing ratios also show a pronounced seasonality, and winter time vertical gradients correlate well with those of CO2. Similarly, SF6 vertical gradients are correlated with CO2 gradients possibly pointing to some anthropogenic origin of the boundary layer CO2 signal during winter. N2O and SF6 also show a slight seasonality with almost the same phasing. The main reasons for the seasonality of both gases are probably transport processes with a possible contribution from stratosphere/troposphere exchange.

Airborne observations of the tropospheric CO2 distribution and its controlling factors over the South Pacific Basin

Highly precise measurements of CO2 mixing ratios were recorded aboard both the NASA DC‐8 and P3‐B aircraft during the Pacific Exploratory Mission‐Tropics conducted in August‐October 1996. Data were obtained at altitudes ranging from 0.1 to 12 km over a large portion of the South Pacific Basin representing the most geographically extensive CO2 data set recorded in this region. These data along with CO2 surface measurements from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) and the National Institute of Water and Atmospheric Research (NIWA) were examined to establish vertical and meridional gradients. The CO2 spatial distribution in the southern hemisphere appeared to be largely determined by interhemispheric transport as air masses with depleted CO2 levels characteristic of northern hemispheric air were frequently observed south of the Intertropical Convergence Zone. However, regional processes also played a role in modulating background concentrations. Comparisons of CO2 with other trace gases indicated that CO2 values were influenced by continental sources. Large scale plumes from biomass burning activities produced enhanced CO2 mixing ratios within the lower to midtroposphere over portions of the remote Pacific. An apparent CO2 source was observed in the NOAA/CMDL surface data between 15°N and 15°S and in the lower altitude flight data between 8°N and 8.5°S with a zone of intensity from 6.5°N to 1°S. Inferred from these data is the presence of a Southern Ocean sink from south of 15°S having two distinct zones seasonally out of phase with one another.

Atmospheric CO_2 monitoring from space

A spectroscopic method of monitoring the atmospheric CO(2) mixing ratio vertical profile from space is described. An experimental design is presented for a solar occultation mode with the O(2)A band in the visible region to retrieve pressure and temperature profiles first, and then several CO(2) bands in the infrared region at 4.3, 2.7, and 2.0 mum to obtain CO(2) mixing ratio profiles. Instrument techniques considered are low resolution Fourier transform spectrometry and radiometry of various bandwidths. Simulations indicate that the precision of the pressure, temperature, and CO(2) mixing ratio measurements for an altitude region 30-10 km are less than 1%, 1 K, and 1%, respectively, for the case of the Fourier transform spectrometer and approximately 1%, 1 K, and 2% for the case of the radiometer. With careful experimental design, measurements can be made with better precision and also can extend below 10 km. This inferred precision of CO(2) may be considered to be good enough for investigating atmospheric dynamics when CO(2) is used as a tracer and also for measuring spatial and temporal variations of CO(2) mixing ratios in the range of 0.5-6.5% of 350 parts per million by volume in the troposphere and the lower stratosphere.