Vertical Distribution Of CO Research Articles

Evaluation of simulated CO2 power plant plumes from six high-resolution atmospheric transport models

Abstract. Power plants and large industrial facilities contribute more than half of global anthropogenic CO2 emissions. Quantifying the emissions of these point sources is therefore one of the main goals of the planned constellation of anthropogenic CO2 monitoring satellites (CO2M) of the European Copernicus program. Atmospheric transport models may be used to study the capabilities of such satellites through observing system simulation experiments and to quantify emissions in an inverse modeling framework. How realistically the CO2 plumes of power plants can be simulated and how strongly the results may depend on model type and resolution, however, is not well known due to a lack of observations available for benchmarking. Here, we use the unique data set of aircraft in situ and remote sensing observations collected during the CoMet (Carbon Dioxide and Methane Mission) measurement campaign downwind of the coal-fired power plants at Bełchatów in Poland and Jänschwalde in Germany in 2018 to evaluate the simulations of six different atmospheric transport models. The models include three large-eddy simulation (LES) models, two mesoscale numerical weather prediction (NWP) models extended for atmospheric tracer transport, and one Lagrangian particle dispersion model (LPDM) and cover a wide range of model resolutions from 200 m to 2 km horizontal grid spacing. At the time of the aircraft measurements between late morning and early afternoon, the simulated plumes were slightly (at Jänschwalde) to highly (at Bełchatów) turbulent, consistent with the observations, and extended over the whole depth of the atmospheric boundary layer (ABL; up to 1800 m a.s.l. (above sea level) in the case of Bełchatów). The stochastic nature of turbulent plumes puts fundamental limitations on a point-by-point comparison between simulations and observations. Therefore, the evaluation focused on statistical properties such as plume amplitude and width as a function of distance from the source. LES and NWP models showed similar performance and sometimes remarkable agreement with the observations when operated at a comparable resolution. The Lagrangian model, which was the only model driven by winds observed from the aircraft, quite accurately captured the location of the plumes but generally underestimated their width. A resolution of 1 km or better appears to be necessary to realistically capture turbulent plume structures. At a coarser resolution, the plumes disperse too quickly, especially in the near-field range (0–8 km from the source), and turbulent structures are increasingly smoothed out. Total vertical columns are easier to simulate accurately than the vertical distribution of CO2, since the latter is critically affected by profiles of vertical stability, especially near the top of the ABL. Cross-sectional flux and integrated mass enhancement methods applied to synthetic CO2M data generated from the model simulations with a random noise of 0.5–1.0 ppm (parts per million) suggest that emissions from a power plant like Bełchatów can be estimated with an accuracy of about 20 % from single overpasses. Estimates of the effective wind speed are a critical input for these methods. Wind speeds in the middle of the ABL appear to be a good approximation for plumes in a well-mixed ABL, as encountered during CoMet.

Vertical evolution of exocometary gas – I. How vertical diffusion shortens the CO lifetime

ABSTRACT Bright debris discs can contain large amounts of CO gas. This gas was thought to be a protoplanetary remnant until it was recently shown that it could be released in collisions of volatile-rich solids. As CO is released, interstellar UV radiation photodissociates CO producing CI, which can shield CO allowing a large CO mass to accumulate. However, this picture was challenged because CI is inefficient at shielding if CO and CI are vertically mixed. Here, we study for the first time the vertical evolution of gas to determine how vertical mixing affects the efficiency of shielding by CI. We present a 1D model that accounts for gas release, photodissociation, ionization, viscous evolution, and vertical mixing due to turbulent diffusion. We find that if the gas surface density is high and the vertical diffusion weak (αv/α < [H/r]2) CO photodissociates high above the mid-plane, forming an optically thick CI layer that shields the CO underneath. Conversely, if diffusion is strong (αv/α > [H/r]2) CI and CO become well mixed, shortening the CO lifetime. Moreover, diffusion could also limit the amount of dust settling. High-resolution ALMA observations could resolve the vertical distribution of CO and CI, and thus constrain vertical mixing and the efficiency of CI shielding. We also find that the CO and CI scale heights may not be good probes of the mean molecular weight, and thus composition, of the gas. Finally, we show that if mixing is strong the CO lifetime might not be long enough for CO to spread interior to the planetesimal belt where gas is produced.

Baseline Subsoil CO2 Gas Measurements and Micrometeorological Monitoring: Above Canopy Turbulence Effects on the Subsoil CO2 Dynamics in Temperate Deciduous Forest

Accurate and continuous measurement of the subsoil CO2 is critical to better understand the terrestrial and atmosphere gas transfer process. This work aims to develop and field test a specific flow system to continuously measure the soil gas concentration (χc) and understand its main physical drivers. Hourly data measured in situ were collected through two dedicated wells at 1 m and 6 m depth coupled with micrometeorological measurement. Our study shows that χc at -1 m was at the lowest in winter and highest in summer. Meanwhile, the seasonal variation of χc at -6m is somewhat unclear. While it is inevitable that temperature plays a significant role, this factor related to biological activity cannot fully explain the variation. The decrease in χc at both depths in summer coincides with an increase of friction velocity, especially during dry periods with R2 of 0.68, which shows strong empirical evidence that wind turbulence plays a significant role in driving the deep soil CO2. A monitoring strategy for gas measurement combining borehole and micrometeorological measurement offers excellent long-term monitoring possibilities to derive the vertical distribution of CO2 and better understand the main physical drivers of gas exchange.

The Influence of Meteorology and Air Transport on CO2 Atmospheric Distribution over South Africa

This paper demonstrates the role of meteorology and air transport in influencing the South African atmospheric CO2 distribution. CO2 data from December 2004 to December 2009 acquired by the Tropospheric Emission Spectrometer (TES) instrument onboard the Aura satellite were used to establish the CO2 vertical distribution at selected regions in South Africa. The Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) atmospheric model backward trajectories were used to determine the long-range air transport impacting on South African CO2 atmospheric distribution and to detect the source areas of air masses impacting on South Africa’s atmosphere. The study found that long-range air transport can result in the accumulation or dilution of atmospheric CO2 at various sites in South Africa, depending on the source region and type of air flow. The long-range air transport from different source regions at the upper air level between the 700 and 500 hPa stable layers and the layer above 500 hPa strengthens the inhomogeneity in the vertical distribution of CO2, which is caused by the decoupling effect of the upper air stable layers. This long-range air transport also involves intercontinental air transport.

Study on carbon dioxide atmospheric distribution over the Southwest Indian Ocean islands using satellite data: Part 2 –the influence of meteorology and air transportation

This investigation is a follow-up to the 3-dimensional distribution analysis of atmospheric CO2 and its surface temporal variation over the Southwest Indian Ocean (SWIO) islands (part 1). Here, we demonstrate the influence of meteorology and the associated air transport on CO2 spatial and vertical distribution determined in part 1. The Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) atmospheric model backward trajectories were used to determine the long-range air transport impacting on SWIO islands CO2 atmospheric loading, and to trace the origin of the air masses impacting on the atmosphere of SWIO islands. This study shows that meteorology and long-range air transport results in accumulation or dilution of atmospheric CO2 at various sites on the SWIO islands and this depends on the source region and type of air flow. Long-range air transport from different source regions at the upper atmospheric levels between the 700 and 500 hPa stable layers and the layer above 500 hPa is found to strengthen the inhomogeneity in the vertical distribution of CO2, caused by the decoupling effect of the upper atmosphere stable layers. This long-range air transport is also found to involve intercontinental air transport.

Detection of carbon monoxide pollution from cities and wildfires on regional and urban scales: the benefit of CO column retrievals from SCIAMACHY 2.3 µm measurements under cloudy conditions

Abstract. In the perspective of the upcoming TROPOMI Sentinel-5 Precursor carbon monoxide data product, we discuss the benefit of using CO total column retrievals from cloud-contaminated SCIAMACHY 2.3 µm shortwave infrared spectra to detect atmospheric CO enhancements on regional and urban scales due to emissions from cities and wildfires. The study uses the operational Sentinel-5 Precursor algorithm SICOR, which infers the vertically integrated CO column together with effective cloud parameters. We investigate its capability to detect localized CO enhancements distinguishing between clear-sky observations and observations with low (< 1.5 km) and medium–high clouds (1.5–5 km). As an example, we analyse CO enhancements over the cities Paris, Los Angeles and Tehran as well as the wildfire events in Mexico–Guatemala 2005 and Alaska–Canada 2004. The CO average of the SCIAMACHY full-mission data set of clear-sky observations can detect weak CO enhancements of less than 10 ppb due to air pollution in these cities. For low-cloud conditions, the CO data product performs similarly well. For medium–high clouds, the observations show a reduced CO signal both over Tehran and Los Angeles, while for Paris no significant CO enhancement can be detected. This indicates that information about the vertical distribution of CO can be obtained from the SCIAMACHY measurements. Moreover, for the Mexico–Guatemala fires, the low-cloud CO data captures a strong outflow of CO over the Gulf of Mexico and the Pacific Ocean and so provides complementary information to clear-sky retrievals, which can only be obtained over land. For both burning events, enhanced CO values are even detectable with medium–high-cloud retrievals, confirming a distinct vertical extension of the pollution. The larger number of additional measurements, and hence the better spatial coverage, significantly improve the detection of wildfire pollution using both the clear-sky and cloudy CO retrievals. Due to the improved instrument performance of the TROPOMI instrument with respect to its precursor SCIAMACHY, the upcoming Sentinel-5 Precursor CO data product will allow improved detection of CO emissions and their vertical extension over cities and fires, making new research applications possible.

CO2 concentration and its spatiotemporal variation in the troposphere using multi-sensor satellite data, carbon tracker, and aircraft observations

Satellite-based atmospheric CO2 observations have provided a great opportunity to improve our understanding of the global carbon cycle. However, thermal infrared (TIR)-based satellite observations, which are useful for the investigation of vertical distribution and the transport of CO2, have not yet been studied as much as the column amount products derived from shortwave infrared data. In this study, TIR-based satellite CO2 products – from Atmospheric Infrared Sounder, Tropospheric Emission Spectrometer (TES), and Thermal And Near infrared Sensor for carbon Observation – and carbon tracker mole fraction data were compared with in situ Comprehensive Observation Network for Trace gases by AIrLiner (CONTRAIL) data for different locations. The TES CO2 product showed the best agreement with CONTRAIL CO2 data resulting in R2 ~ 0.87 and root-mean-square error ~0.9. The vertical distribution of CO2 derived by TES strongly depends on the geophysical characteristics of an area. Two different climate regions (i.e., southeastern Japan and southeastern Australia) were examined in terms of the vertical distribution and transport of CO2. Results show that while vertical distribution of CO2 around southeastern Japan was mainly controlled by horizontal and vertical winds, horizontal wind might be a major factor to control the CO2 transport around southeastern Australia. In addition, the vertical transport of CO2 also varies by region, which is mainly controlled by anthropogenic CO2, and horizontal and omega winds. This study improves our understanding of vertical distribution and the transport of CO2, both of which vary by region, using TIR-based satellite CO2 observations and meteorological variables.

Modulation of Midtropospheric CO2 by the South Atlantic Walker Circulation*

Abstract Midtropospheric CO2 data from the Atmospheric Infrared Sounder (AIRS) are used in this study to explore the variability of CO2 over the South Atlantic Ocean. It was found that the area-averaged CO2 over the South Atlantic Ocean is less than that over South America by about 1 ppm during December–March. This CO2 contrast is due to the large-scale vertical circulation over this region. During December–March, there is sinking motion over the South Atlantic Ocean. The sinking motion brings high-altitude air with a slightly lower concentration of CO2 to the midtroposphere. Meanwhile, air rising over South America brings near-surface air with a higher concentration of CO2 to the midtroposphere. As a result, the AIRS midtropospheric CO2 concentration is lower over the South Atlantic Ocean than over South America during December–March. The detrended AIRS midtropospheric CO2 difference correlates well with the inverted and detrended 400-hPa vertical pressure velocity difference between the South Atlantic and South America. Results obtained from this study demonstrate the strong impact of large-scale circulation on the vertical distribution of CO2 in the free troposphere and suggest that midtropospheric CO2 measurements can be used as an innovative observational constraint on the simulation of large-scale circulations in climate models.

How well do tall-tower measurements characterize the CO<sub>2</sub> mole fraction distribution in the planetary boundary layer?

Abstract. Planetary boundary layer (PBL) CO2 mole fraction data are needed by transport models and carbon budget models as both input and reference for validation. The height of in situ CO2 mole fraction measurements is usually different from that of the model levels where the data are needed; data from short towers, in particular, are difficult to utilize in atmospheric models that do not simulate the surface layer well. Tall-tower CO2 mole fraction measurements observed at heights ranging from 10 to 115 m above ground level at a rural site in Hungary and regular airborne vertical mole fraction profile measurements (136 vertical profiles) above the tower allowed us to estimate how well a tower of a given height could estimate the CO2 mole fraction above the tower in the PBL. The statistical evaluation of the height-dependent bias between the real PBL CO2 mole fraction profile (measured by the aircraft) and the measurement at a given elevation above the ground was performed separately for the summer and winter half years to take into account the different dynamics of the lower troposphere and the different surface CO2 flux in the different seasons. The paper presents (1) how accurately the vertical distribution of CO2 in the PBL can be estimated from the measurements on the top of a tower of height H; (2) how tall of a tower would be needed for the satisfaction of different requirements on the accuracy of the estimation of the CO2 vertical distribution; (3) how accurate of a CO2 vertical distribution estimation can be expected from the existing towers; and (4) how much improvement can be achieved in the accuracy of the estimation of CO2 vertical distribution by applying the virtual tall-tower concept.

Vertical distribution of CO2 in the atmospheric boundary layer: Characteristics and impact of meteorological variables

Knowledge of vertical CO2 distribution is important for development of CO2 transport models and calibration/validation of satellite-borne measurements. In this study, vertical profiles of CO2 concentration within 0–1000 m were measured using a tethered balloon at a suburban site in Xiamen, which is undergoing fast urbanization. The characteristics of CO2 vertical distribution were investigated under both stable and convective boundary-layer conditions. The correlation of ground level CO2 concentrations and those at high altitudes decreased with altitude and show significant correlation in the first 300 m with R = 0.78 at 100 m, R = 0.52 at 200 m, R = 0.40 at 300 m (P < 0.01). The correlation keeps almost constant for 300–800 m, and there is no obvious correlation at 800 m, indicating that the impact of ground level CO2 was restricted within the 300 m above the ground. When comparing the vertical profiles obtained at different times during a 24 h period, it was found that CO2 concentration exhibited more obvious diurnal pattern at surface level than at high altitude because of the variation of sources and sinks of CO2 at ground level. Most profiles demonstrated declining trends of CO2 concentration with increasing altitude. The vertical profiles of CO2 were fitted to obtain an empirical equation for estimating CO2 vertical concentration in the lower atmosphere (0–1000 m): y = −75.04 + 1.17 × 109e−x/28.01, R2 = 0.59 (P < 0.05). However, for some cases opposite patterns were observed that the CO2 concentration profiles showed a turning point at a certain altitude or little variation with altitude under certain meteorological conditions. The atmospheric boundary layer depth and atmospheric stability are two major factors controlling the vertical structure of CO2 profile. The results would improve our understanding of the spatial and temporal variation of CO2 in urban environment, which would facilitate using 3-D transport model to study the impacts of CO2 on urban environment.

Effects of experimental drying intensity and duration on respiration and methane production recovery in fen peat incubations

Drying and rewetting to a variable extent influence the C gas exchange between peat soils and the atmosphere. We incubated a decomposed and compacted fen peat and investigated in two experiments 1) the vertical distribution of CO2 and CH4 production rates and their response to drying and 2) the effects of temperature, drying intensity and duration on CO2 production rates and on CH4 production recovery after rewetting. Surface peat down to 5 cm contributed up to 67% (CO2) and above 80% (CH4) of the depth-aggregated (50 cm) production. As CO2 production sharply decreased with depth water table fluctuations in deeper peat layers are thus not expected to cause a substantial increase in soil respiration in this site. Compared to anaerobic water saturated conditions drying increased peat CO2 production by a factor between 1.4 and 2.1. Regarding the effects of the studied factors, warmer conditions increased and prolonged drying duration decreased CO2 production whereas the soil moisture level had little influence. No significant interactions among factors were found. Short dry events under warmer conditions are likely to result in greatest peaks of CO2 production rates. Upon rewetting, CH4 production was monitored over time and the recovery was standardized to pre-drying levels to compare the treatment effects. Methane production increased non-linearly over time and all factors (temperature, drying intensity and duration) influenced the pattern of post-drying CH4 production. Peat undergoing more intense and longer drying events required a longer lag time before substantial CH4 production occurred and warmer conditions appeared to speed up the process.

RESOLVING THE CO SNOW LINE IN THE DISK AROUND HD 163296

We report Submillimeter Array (SMA) observations of CO (J=2--1, 3--2 and 6--5) and its isotopologues (13CO J=2--1, C18O J=2--1 and C17O J=3--2) in the disk around the Herbig Ae star HD 163296 at ~2" (250 AU) resolution, and interpret these data in the framework of a model that constrains the radial and vertical location of the line emission regions. First, we develop a physically self-consistent accretion disk model with an exponentially tapered edge that matches the spectral energy distribution and spatially resolved millimeter dust continuum emission. Then, we refine the vertical structure of the model using wide range of excitation conditions sampled by the CO lines, in particular the rarely observed J=6--5 transition. By fitting 13CO data in this structure, we further constrain the vertical distribution of CO to lie between a lower boundary below which CO freezes out onto dust grains (T ~ 19 K) and an upper boundary above which CO can be photodissociated (the hydrogen column density from the disk surface is ~ 10^{21} cm-2). The freeze-out at 19 K leads to a significant drop in the gas-phase CO column density beyond a radius of ~155 AU, a "CO snow line" that we directly resolve. By fitting the abundances of all CO isotopologues, we derive isotopic ratios of 12C/13C, 16O/18O and 18O/17O that are consistent with quiescent interstellar gas-phase values. This detailed model of the HD 163296 disk demonstrates the potential of a staged, parametric technique for constructing unified gas and dust structure models and constraining the distribution of molecular abundances using resolved multi-transition, multi-isotope observations.

On the HCN and CO 2 abundance and distribution in Jupiter's stratosphere

Observations of Jupiter by Cassini/CIRS, acquired during the December 2000 flyby, provide the latitudinal distribution of HCN and CO 2 in Jupiter's stratosphere with unprecedented spatial resolution and coverage. Following up on a preliminary study by Kunde et al. [Kunde, V.G., and 41 colleagues, 2004. Science 305, 1582–1587], the analysis of these observations leads to two unexpected results (i) the total HCN mass in Jupiter's stratosphere in 2000 was ( 6.0 ± 1.5 ) × 10 13 g , i.e., at least three times larger than measured immediately after the Shoemaker–Levy 9 (SL9) impacts in July 1994 and (ii) the latitudinal distributions of HCN and CO 2 are strikingly different: while HCN exhibits a maximum at 45° S and a sharp decrease towards high Southern latitudes, the CO 2 column densities peak over the South Pole. The total CO 2 mass is ( 2.9 ± 1.2 ) × 10 13 g . A possible cause for the HCN mass increase is its production from the photolysis of NH 3, although a problem remains because, while millimeter-wave observations clearly indicate that HCN is currently restricted to submillibar ( ∼ 0.3 mbar ) levels, immediate post-impact infrared observations have suggested that most of the ammonia was present in the lower stratosphere near 20 mbar. HCN appears to be a good atmospheric tracer, with negligible chemical losses. Based on 1-dimensional (latitude) transport models, the HCN distribution is best interpreted as resulting from the combination of a sharp decrease (over an order of magnitude in K y y ) of wave-induced eddy mixing poleward of 40° and an equatorward transport with ∼ 7 cm s −1 velocity. The CO 2 distribution was investigated by coupling the transport model with an elementary chemical model, in which CO 2 is produced from the conversion of water originating either from SL9 or from auroral input. The auroral source does not appear adequate to reproduce the CO 2 peak over the South Pole, as required fluxes are unrealistically high and the shape of the CO 2 bulge is not properly matched. In contrast, the CO 2 distribution can be fit by invoking poleward transport with a ∼ 30 cm s −1 velocity and vigorous eddy mixing ( K y y = 2 × 10 11 cm 2 s −1 ). While the vertical distribution of CO 2 is not measured, the combined HCN and CO 2 results imply that the two species reside at different stratospheric levels. Comparing with the circulation regimes predicted by earlier radiative-dynamical models of Jupiter's stratosphere, and with inferences from the ethane and acetylene stratospheric latitudinal distribution, we suggest that CO 2 lies in the middle stratosphere near or below the 5-mbar level.

Large horizontal gradients in atmospheric CO at the synoptic scale as seen by spaceborne Measurements of Pollution in the Troposphere

We have examined the influence of synoptic processes on the distribution of atmospheric CO as observed by the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument. In the MOPITT data, large horizontal gradients in CO, coherent at the synoptic scale, have been observed. The concentration of CO varies rapidly by as much as 50–100% across distances of ∼100 km, forming distinct boundaries in the CO distribution. These can last one to several days and span horizontal distances of 600–1000 km. On average, such events were observed in the MOPITT CO daily images once every 3–4 days over North America in spring and summer 2000. We focused on three case studies over North America in August 2000 to understand the mechanisms responsible for the large gradients in CO. Through an analysis of meteorological data from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis, parcel trajectory modeling, and global three‐dimensional chemical transport modeling, we found that the large horizontal gradients typically reflect the differential vertical and horizontal transport of air with different chemical signatures. In the first case, the large gradients in CO over North Dakota resulted from the lifting ahead of a cold front that transported boundary layer air enriched with CO from forest fires in Montana, combined with the descent of clean air from the Canadian Prairies behind the front. In the second case, the large gradients over northeastern Texas were produced by the convective lifting over Arkansas of air with high concentrations of CO from the oxidation of volatile organic compounds and the onshore transport of clean air from the Gulf of Mexico. In the third case, we examined an example of outflow of surface pollution from North America by a cyclone. The largest gradients in this case were observed along the boundary between the boundary layer air transported by the warm conveyor belt ahead of the cold front and the clean air transported from the Atlantic by the semipermanent high‐pressure system in the central Atlantic. Our results demonstrate that MOPITT can capture the influence of synoptic processes on the horizontal and vertical distribution of CO. The large gradients in CO observed on synoptic scales represent valuable information that can be exploited to improve our understanding of atmospheric CO. In particular, these results suggest that the MOPITT observations provide a useful data set with which to address a range of issues from air quality on local/regional scales to long‐range transport of pollution on continental/global scales.

Global carbon monoxide vertical distributions from spaceborne high-resolution FTIR nadir measurements

Abstract. This paper presents the first global distributions of CO vertical profiles retrieved from a thermal infrared FTS working in the nadir geometry. It is based on the exploitation of the high resolution and high quality spectra measured by the Interferometric Monitor of Greenhouse gases (IMG) which flew onboard the Japanese ADEOS platform in 1996-1997. The retrievals are performed with an algorithm based on the Optimal Estimation Method (OEM) and are characterized in terms of vertical sensitivity and error budget. It is found that most of the IMG measurements contain between 1.5 and 2.2 independent pieces of information about the vertical distribution of CO from the lower troposphere to the upper troposphere-lower stratosphere (UTLS). The retrievals are validated against coincident NOAA/CMDL in situ surface measurements and NDSC/FTIR total columns measurements. The retrieved global distributions of CO are also found to be in good agreement with the distributions modeled by the GEOS-CHEM 3D CTM, highlighting the ability of IMG to capture the horizontal as well as the vertical structure of the CO distributions.

Analytical estimation of the vertical distribution of CO 2 production within soil: application to a Japanese temperate forest

We present methods, based on an analytical solution to a diffusion equation, for estimating the vertical distribution of the rate of CO 2 production within soil. The first method assumes an a priori equation that represents the profile of CO 2 production. The second method divides the soil into four layers, from the ground surface to a depth of 80 cm; within each layer, constant CO 2 production is assumed. These methods were applied to a secondary deciduous temperate forest in Japan. Soil respiration and CO 2 concentrations within the soil pores were measured in the forest from March to December of 1998. The value of Q 10, the factor by which metabolic processes increase for each 10 °C increase in temperature, was estimated to be 2.55, using the soil temperature at a depth of 10 cm. The annual soil respiration was estimated to be 642 ± 91 g C m −2 y −1. The CO 2 concentration within soil pores increased with soil depth in every season, and showed temperature dependency at all depths, which was similar to the relationship between soil respiration and soil temperature. By applying the proposed methods, the profiles of the actual CO 2 concentrations within soil pores were well reproduced. Within soil, the amplitude of the seasonal variation in the CO 2 production rate was larger in the shallow soil layers than in the deep layers. The CO 2 production rate in the shallow soil layers was highly correlated with soil temperature, and its response to soil temperature was more sensitive than that estimated from the CO 2 efflux from the soil surface. It was found that the temperature sensitivity of the CO 2 production rate differed between the shallow and deep soil layers; this would affect the estimated value of Q 10. Adding to the necessity of distinguishing heterotrophic and autotrophic respiration, it is suggested that the way in which they are distributed vertically within soil is critical for predicting soil respiration, and should be included in the parameterization of soil respiration.

Vertical and meridional distributions of the atmospheric CO2 mixing ratio between northern midlatitudes and southern subtropics

The atmospheric CO2 mixing ratio was measured using a continuous measurement system onboard a Gulfstream‐II aircraft between the northern midlatitudes and the southern subtropics during the Biomass Burning and Lightning Experiment Phase A (BIBLE A) campaign in September–October 1998. The vertical distribution of CO2 over tropical regions was almost constant from the surface to an altitude of 13 km. CO2 enhancements from biomass burning and oceanic release were observed in the tropical boundary layer. Measurements in the upper troposphere indicate interhemispheric exchange was effectively suppressed between 2°N–7°N. Interhemispheric transport of air in the upper troposphere was suppressed effectively in this region. The CO2 mixing ratios in the Northern and Southern Hemispheres were almost constant, with an average value of about 365 parts per million (ppm) and 366 ppm, respectively. The correlation between the CO2 and NOy mixing ratios observed north of 7°N was apparently different from that obtained south of 2°N. This fact strongly supports the result that the north‐south boundary in the upper troposphere during BIBLE A was located around 2°N–7°N as the boundary is not necessary a permanent feature.

Stratospheric depletion of CO on Titan

A deep stratospheric depletion of CO is found in Titan's atmosphere comparing millimetric and infrared observations [Marten et al., 1988; Lutz et al., 1983]. We suggest that adsorption of CO on aerosols in the region of Titan's atmosphere where methane is expected to condense may change the vertical distribution of CO below ≈ 40 km. Aerosols slowly pervading through the methane condensation region could transport enough CO to generate the observed tropospheric enrichment provided the sticking coefficient ε (fraction of collisions yielding adsorption) is 6 10−4, assuming the same eddy diffusion coefficient K as in the Earth troposphere. In the case of a lower mixing rate, generally favoured, smaller values of ε are allowed (down to ≈ 10−6). Besides, the final radius of methane particles, just above the region where methane evaporates (below ≈ 10 km), must be 100 μm within a factor of 10. The hypothesis presented in this paper, if it is confirmed by laboratory measurements, could be an indirect evidence for large amounts of CH4 ice in the Titanian atmosphere.

The spectrum of Saturn from 1990 to 2230 cm −1: Abundances of AsH 3, CH 3D, CO, GeH 4, NH 3, and PH 3

We have investigated the mole fractions of six gases (AsH 3, CH 3D, CO, GeH 4, NH 3, and PH 3) from extensive computer modeling of a high-resolution spectrum of Saturn from 1994 to 2229 cm −1 (4.5 to 5.0 μm). Five new AsH 3 spectral features and three previously observed absorptions were detected, leaving no doubt as to the presence of this gas in Saturn. The mole fraction of AsH 3 is 3 × 10 −9, in agreement with earlier work and 10 times higher than that found in Jupiter. Thirteen lines of CO were detected, including eight new lines. Our CO abundance is lower than previous estimates, which we attribute to an improved atmospheric model. We find that the CO mole fraction is 1 × 10 −9 if its distribution is uniform and 2.5 × 10 −8 if concentrated in the stratosphere at pressures P < 80 mbar. The detection of one high- J line of CO in Saturn's spectrum, P14, favors a tropospheric distribution but the evidence is not strong enough to make a firm conclusion regarding the vertical distribution of CO. The PH 3 abundance increases dramatically below the photochemically active portion of the atmosphere. For P < 400 mbar the PH 3 mole fraction was fixed at 1 × 10 −6, in agreement with previous work, which produced a good fit to that region of Saturn's 5-μm spectrum dominated by reflected sunlight. At P > 400 mbar, however, we find that the PH 3 mole fraction is 7 −2 +3 × 10 −6, which indicates a surprisingly high elemental abundance of P in Saturn. The mole fraction of CH 3D is (3.3 ± 1.5) × 10 −7, in general agreement with values determined at other wavelengths, which leads to a D/H ratio of (1.7 ± 1.1) × 10 −5. Our constraints to the abundances of GeH 4 and NH 3 are weak. We find that the mole fraction of GeH 4 is (4 ± 4) × 10 −10 and that of NH 3 is ≤ 3 × 10 −4. The observed elemental abundances of P and As are important as remnants of the solid component of the solar nebula. Their pattern of enrichment in Jupiter and Saturn appears to be different than that for C and N.

Far‐infrared measurement of stratospheric carbon monoxide

The stratospheric vertical distribution of CO is obtained from balloon based far infrared limb thermal emission spectra by analyzing several limb sequences of the R8 and R1 spectral lines at 34.588 cm−1 and 49.932 cm−1 respectively. This constitutes the first determination of the stratospheric CO profile from infrared thermal emission spectra. The results indicating 24.6±7.6 ppbv at 21 km and 34.4±10.1 ppbv at 37 km are compared with the remote sensing and in‐situ measurements by other groups and with photochemical‐dynamical model calculations.