Trace Gas Mixing Ratios Research Articles

Measurement of fine particulate and gas-phase species during the New Year's fireworks 2005 in Mainz, Germany

The chemical composition and chemically resolved size distributions of fine aerosol particles were measured at high time resolution (5 min) with a time-of-flight aerosol mass spectrometer (TOF-AMS) during the New Year's 2005 fireworks in Mainz, central Germany. In addition, particle number concentrations and trace gas concentrations were measured using a condensation particle counter (CPC) and a proton transfer reaction mass spectrometer (PTR-MS). The main non-refractory components of the firework aerosol were potassium, sulfate, total organics and chloride. Increased trace gas mixing ratios of methanol, acetonitrile, acetone and acetaldehyde were observed. Aerosol nitrate and ammonium concentrations were not significantly affected by the fireworks as well as the measured aromatic trace gases. The sub-micron aerosol concentrations peaked about 20 min after midnight with total mass concentrations larger than 600 μg m −3. The trace gas concentrations peaked about 30 min later. Using the sulfur-to-potassium concentration ratio measured in another fireworks aerosol, it was for the first time possible to estimate the relative ionization efficiency of aerosol potassium, measured with the TOF-AMS. Here we found a value of RIE K=2.9.

First results from the OMI rotational Raman scattering cloud pressure algorithm

We have developed an algorithm to retrieve scattering cloud pressures and other cloud properties with the Aura Ozone Monitoring Instrument (OMI). The scattering cloud pressure is retrieved using the effects of rotational Raman scattering (RRS). It is defined as the pressure of a Lambertian surface that would produce the observed amount of RRS consistent with the derived reflectivity of that surface. The independent pixel approximation is used in conjunction with the Lambertian-equivalent reflectivity model to provide an effective radiative cloud fraction and scattering pressure in the presence of broken or thin cloud. The derived cloud pressures will enable accurate retrievals of trace gas mixing ratios, including ozone, in the troposphere within and above clouds. We describe details of the algorithm that will be used for the first release of these products. We compare our scattering cloud pressures with cloud-top pressures and other cloud properties from the Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument. OMI and MODIS are part of the so-called A-train satellites flying in formation within 30 min of each other. Differences between OMI and MODIS are expected because the MODIS observations in the thermal infrared are more sensitive to the cloud top whereas the backscattered photons in the ultraviolet can penetrate deeper into clouds. Radiative transfer calculations are consistent with the observed differences. The OMI cloud pressures are shown to be correlated with the cirrus reflectance. This relationship indicates that OMI can probe through thin or moderately thick cirrus to lower lying water clouds.

Trace gas exchange and gas phase chemistry in a Norway spruce forest: A study with a coupled 1-dimensional canopy atmospheric chemistry emission model

Numerical modelling is an efficient tool to investigate the role of chemical degradation of biogenic volatile organic compounds (BVOC) and the effect of dynamical processes on BVOC and product mixing ratios within and above forest canopies. The present study shows an application of the coupled canopy-chemistry model CACHE to a Norway spruce forest at the Waldstein (Fichtelgebirge, Germany). Simulated courses of temperature, trace gas mixing ratios, and fluxes are compared with measurements taken during the BEWA2000 field campaigns. The model permits the interpretation of the observed diurnal course of ozone and VOC by investigating the role of turbulent exchange, chemical formation and degradation, emission, and deposition during the course of the day. The simulation results show that BVOC fluxes into the atmosphere are 10–15% lower than the emission fluxes on branch basis due to chemical BVOC degradation within the canopy. BVOC degradation by the NO 3 radical was found to occur in the lower part of the canopy also during daytime. Furthermore, the simulations strongly indicate that further research is still necessary concerning the emission and deposition of aldehydes and ketones.

Measurements of Trace Gases in the Inflow of South China Sea Background Air and Outflow of Regional Pollution at Tai O, Southern China

We present a 16-month record of ozone (O3), carbon monoxide (CO), total reactive nitrogen (NO y ), sulphur dioxide (SO2), methane (CH4), C2 – C8 non-methane hydrocarbons (NMHCs), C1 – C2 halocarbons, and dimethyl sulfide (DMS) measured at a southern China coastal site. The study aimed to establish/update seasonal profiles of chemically active trace gases and pollution tracers in subtropical Asia and to characterize the composition of the `background' atmosphere over the South China Sea (SCS) and of pollution outflow from the industrialized Pearl River Delta (PRD) region and southern China. Most of the measured trace gases of anthropogenic origin exhibited a winter maximum and a summer minimum, while O3 showed a maximum in autumn which is in contrast to the seasonal behavior of O3 in rural eastern China and in many mid-latitude remote locations in the western Pacific. The data were segregated into two groups representing the SCS background air and the outflow of regional continental pollution (PRD plus southern China), based on CO mixing ratios and meteorological conditions. NMHCs and halocarbon data were further analyzed to examine the relationships between their variability and atmospheric lifetime and to elucidate the extent of atmospheric processing in the sampled air parcels. The trace gas variability (S) versus lifetime (τ) relationship, defined by the power law, S lnx = Aτ− b, (where X is the trace gas mixing ratio) gives a fit parameter A of 1.39 and exponent b of 0.42 for SCS air, and A of 2.86 and b of 0.31 for the regional continental air masses. An examination of ln[n-butane]/ln[ethane] versus ln[propane]/ln[ethane] indicates that their relative abundance was dominated by mixing as opposed to photochemistry in both SCS and regional outflow air masses. The very low ratios of ethyne/CO, propane/ethane and toluene/benzene suggest that the SCS air mass has undergone intense atmospheric processing since these gases were released into the atmosphere. Compared to the results from other polluted rural sites and from urban areas, the large values of these species in the outflow of PRD/southern China suggest source(s) emitting higher levels of ethyne, benzene, and toluene, relative to light alkanes. These chemical characteristics could be unique indicators of anthropogenic emissions from southern China.

Regional and global trace gas distributions and inferred transports in the upper troposphere and lower stratosphere

Trace gas mixing ratios were measured in the upper troposphere and lower stratosphere during the second mission of the Cryogenic Infrared Spectrometers and Telescopes (CRISTA) experiment in August 1997. Water vapor data at high vertical and horizontal resolution are presented here. Respective data for CFC 11 (CFCl3) are given in a future paper by V. Kuell et al. (Tropopause region temperatures and CFC 11 mixing ratios from CRISTA 2, submitted to Journal of Geophysical Research, 2004). Some ozone data are also available. Zonal mean mixing ratios of water vapor are compared to several other measurements, and good agreement is obtained. Data variance of all three gases is high and is mostly attributable to atmospheric fluctuations rather than instrument noise. Diffusive (“eddy”) fluxes were derived from these fluctuations for all three gases. They were converted to meridional eddy coefficients Kyy by means of respective mixing ratio gradients. Kyy values obtained from CFC 11 and H2O show a close correlation (r = 0.62). This suggests that water vapor may be a usable tracer at medium latitudes. (This does not include the tropics, where our Kyy values appear to be unreliable.) Our Kyy values are substantially higher than those frequently used in the literature. Another difference is that our summer values are larger on average than the winter ones (by a factor of 2). A similar result, however, is seen in the effective diffusivities Keff of Haynes and Shuckburgh (2000a, 2000b) (hereinafter referred to as HS a,b). There are other agreements of the two data sets Kyy and Keff: HS a,b discuss a number of transport barriers (equator and tropopause). These are found in a very similar way in our data. The latitude structures of the Kyy and Keff coefficients can be compared at three altitude levels. These patterns are also found to be quite similar.

Global simulation of tropospheric ozone using the University of Maryland Chemical Transport Model (UMD‐CTM): 2. Regional transport and chemistry over the central United States using a stretched grid

We use the stretched‐grid version of the three‐dimensional global University of Maryland Chemical Transport Model (UMD‐CTM) to examine the effects of mesoscale meteorological features such as fronts and deep convection on regional‐scale chemistry and transport. The stretched‐grid model simulation, with a grid configuration featuring a mesoscale resolution region centered over the central United States, was conducted for June 1985, and evaluated through comparisons with a set of aircraft observations of trace gases. We also present results from a uniform‐grid UMD‐CTM simulation with a more conventional 2° × 2.5° horizontal resolution for the same time period to examine how well the stretched‐grid global model simulates mesoscale features. The changes in middle and upper tropospheric CO and O3 due to convection from the model simulations are in good agreement with the range of measurements. The stretched‐grid model shows better agreement with measurements than the uniform‐grid model for the enhancement of trace gases in upper troposphere outflow due to deep convection and for the gradient of trace gas mixing ratios across a cold front. Peak convective enhancement of CO in the upper troposphere is larger in the stretched‐grid model simulation than in the uniform‐grid simulation, indicating a better representation of locally focused deep convective transport of polluted boundary layer air in the former. This type of vertical transport feature must be handled accurately if a model is to be used for intercontinental transport calculations. However, we find that deep convection in both model simulations, although better simulated in the stretched‐grid model, is too widespread and too frequent. We find that net ozone production in the polluted boundary layer is ∼15% less in the fine‐grid region (0.5° resolution) of the stretched‐grid model than in the same region of the 2° × 2.5° model due to less artificial dilution of ozone precursors. The net ozone production in convective outflow plumes is also smaller in the stretched‐grid model than in the uniform‐grid model. We estimate the net flux of ozone from North America in the lowest 7 km to be 10 Gmol d−1 for the month of June using the results from the stretched‐grid simulation. This value includes direct horizontal boundary layer flux, ozone that has been vertically transported from the boundary layer to free troposphere, and ozone that had been produced photochemically in the free troposphere.

Variability in ammonium nitrate formation and nitric acid depletion with altitude and location over California

Spatial variations in the partitioning of nitrate between gas phase nitric acid (HNO3) and particulate ammonium nitrate were observed using airborne measurements of trace gas mixing ratios, particle size distributions, and particle composition. During the Intercontinental Transport and Chemical Transformation experiment in April and May 2002 the NOAA WP‐3 aircraft flew up to 8 km altitude on 11 research flights from Monterey, California. The formation of semivolatile aerosols was studied by examining the enhancement of fine‐particulate ammonium nitrate and depletion of gas‐phase HNO3 over the San Joaquin Valley, Los Angeles Basin, and Mojave Desert. Gas‐phase particle precursors, HNO3 and ammonia (NH3), were converted to particulate ammonium nitrate at higher altitudes within the boundary layer. These particle layers were a consequence of lower ambient temperatures that caused a reduction of the dissociation constant for ammonium nitrate aerosol so that gas phase HNO3 was depleted and particle mass was formed. The resulting vertical gradients in particulate matter and HNO3 were observed in well‐mixed boundary layers where other directly emitted trace gases (CO) and secondary pollutants (O3) exhibited no vertical gradients. Hence the equilibrium between the gas and particle phases occurred faster than boundary layer mixing times and chemical rather than meteorological effects were responsible for the layers of enhanced particulate matter aloft. Coincident HNO3 depletion and ammonium nitrate formation was also observed downwind from regions characterized by large agricultural NH3 emissions in the Los Angeles Basin and San Joaquin Valley.

Trace gas and radical diurnal behavior in the marine boundary layer during INDOEX 1999

Selected trace gas mixing ratios (i.e., peroxy radicals (RO*2 = HO2 + ΣRO2), nonmethane hydrocarbons (NMHCs), O3, CO, HCHO, and NO) and photolysis rate coefficients of j(NO2) and j(O(1D)) were measured in the marine boundary layer (MBL) over the Indian Ocean. The measurements were performed during February, March, and April 1999 as a part of the Indian Ocean Experiment (INDOEX) on board the research vessel R/V Ronald H. Brown. During the campaign, air parcels having different origins and consequently variable compositions were encountered, but all air masses, including those heavily polluted with NMHCs and aerosols, were in the regime of rapid photochemical ozone destruction. The influence of aerosols on the photolysis frequencies was investigated by comparison of measurements and results from the radiative transfer model PHOTOST: the high optical depth (up to 0.6) and low single scattering albedo of the aerosol reduces the UV flux at the surface substantially downwind of India and Arabia causing, for instance, a reduction in j(O(1D)) by up to 40%. The diurnal behavior of the trace gases and parameters in the MBL has been investigated by using a time‐dependent zero‐dimensional chemical model. Significant differences between the diurnal behavior of RO*2 derived from the model and observed in measurements were identified. The measured HCHO concentrations differed from the model results and are best explained by some missing chemistry involving low amounts of Cl. Other possible processes describing these two effects are presented and discussed.

Chemical characteristics assigned to trajectory clusters during the MINOS campaign

Abstract. During the Mediterranean Intensive Oxidant Study (MINOS) in August 2001 a total of 14 measurement flights were performed with the DLR Falcon jet aircraft from Heraklion, Crete. One objective of this campaign was to investigate the role of long-range transport of pollutants into the Mediterranean area. An analysis of 5-day back trajectories indicates that in the lower troposphere (0-4 km) air masses originated from eastern and western Europe, in the mid-troposphere (4-8 km) from the North Atlantic Ocean region and in the upper troposphere (8-14 km) from North Atlantic Ocean/North America (NANA) as well as South Asia. We allocated all back trajectories to clusters based on their ending height and source region. The mixing ratios of ozone, nitrogen oxide, total reactive oxidized nitrogen (NOy), formaldehyde, methanol, acetonitrile, acetone, peroxyacetyl nitrate (PAN), carbon dioxide, carbon monoxide and methane measured along the flight tracks are examined in relation to the different cluster trajectories. In the lower troposphere the mean trace gas mixing ratios of the eastern Europe cluster trajectories were significantly higher than those from western Europe. In the upper troposphere air from the NANA region seems to be influenced by the stratosphere, in addition, air masses were transported from South Asia, being influenced by strong convection in the Indian monsoon.

Calibration procedures and correction of detector signal relaxations for the CRISTA infrared satellite instrument.

Remote sensing from space has become a common method for deriving geophysical parameters such as atmospheric temperature and composition. The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument was designed to sound the middle and the upper atmosphere (10-180 km) with high spatial resolution. Atmospheric IR emissions were measured with Si:Ga bulk or Si:As blocked impurity band detectors for a wavelength interval of 4-17 microm and Ge:Ga bulk detectors for 56-71 microm. An overview of the calibration of the instrument and the correction of detector signal relaxations for the Si:Ga detectors are given, both of which are necessary to provide high-quality IR radiance data as input for the retrieval of atmospheric temperature and trace gas mixing ratios. Laboratory and flight data are shown to demonstrate the quality of the results.

Pointing and temperature retrieval from millimeter‐submillimeter limb soundings

Passive microwave limb sounding instruments like the Millimeter‐Wave Atmospheric Sounder (MAS) or the Microwave Limb Sounder (MLS) observe dedicated oxygen lines for the derivation of temperature and pointing information, since these quantities are essential for the quality of the retrieval of the trace gas mixing ratio. Emission lines of oxygen are chosen because the volume mixing ratio (VMR) profile is known. In this paper, we demonstrate the capabilities of a new and innovative method by means of which accurate temperature and pointing information can be gathered from other strong spectral features like ozone lines, without including accurate knowledge of the VMR profile of these species. For this purpose, retrievals from two observation bands with a bandwidth of about 10 GHz each, one including an oxygen line, have been compared. A full error analysis was performed with respect to critical instrument and model parameters, such as uncertainties in the antenna pattern, calibration uncertainties, random pointing error, baseline ripples, baseline discontinuities, and spectroscopic parameters. The applied inversion algorithm was the optimal estimation method. For the selected scenario and instrumental specifications we find that the retrieval of a pointing offset and the atmospheric temperature profile can be achieved with a good accuracy. The retrieval precision of the pointing offset is better than 24 m. The retrieval precision of the temperature profile is better than 2 K for altitudes ranging from 10 to 40 km. Systematic errors (due to model parameter uncertainties) are somewhat larger than these purely statistical errors. Investigations carried out for different atmospheric states or different instrumental specifications show similar results.

Trace gas composition of midlatitude cyclones over the western North Atlantic Ocean: A seasonal comparison of O3 and CO

The regional‐ to synoptic‐scale transport of trace gases from North America to the western North Atlantic Ocean (WNAO) is largely controlled by midlatitude cyclones. The four primary airstreams that compose these cyclones, the warm conveyor belt (WCB), cold conveyor belt (CCB), dry airstream (DA), and post cold front (PCF) airstream, exhibit characteristic trace gas mixing ratios that vary seasonally. The present study compares ozone and CO mixing ratios measured in these four airstreams during spring 1996 and late summer/early autumn 1997. The three main influences on this seasonal variation of ozone and CO are surface emissions heterogeneity, photochemistry, and stratosphere/troposphere exchange efficiency. The more southerly springtime cyclone tracks account for nearly 50% of the increase of lower troposphere CO from late summer/early autumn to spring. The remainder of the variation is due to the seasonal cycle of background CO. Stratosphere/troposphere exchange occurs in every DA; however, the seasonal cycle of ozone in the lowermost stratosphere allows greater quantities of ozone to enter the troposphere during spring. Net photochemical ozone production occurs in the late summer/early autumn WCB at all levels and in the lower troposphere PCF. In contrast, springtime net ozone production appears absent from all airstreams, with the CCB influenced by ozone destruction. Ozone and CO are greater in spring, but the relative mixing ratios between airstreams are roughly the same in both seasons. NOx/CO emissions ratios vary across the midlatitudes according to socioeconomic factors. It is expected that the emissions variation influences the ozone production efficiency of the cyclone airstreams that draw from these regions.

What is the concentration footprint of a tall tower?

Studies that have attempted to estimate sources and sinks of trace gases such as CO2 with inverse calculations unanimously identify the lack of continental stations as a prime obstacle. Continental stations have traditionally been avoided because of the difficulty of interpretation due to large time‐variability of trace substance mixing ratios. Large variability is caused by the proximity to the strongly variable sources in space and time and the complicated airflow within the lowermost 100–200 m of the planetary boundary layer. To address the need for continental stations and to overcome the problems associated with them, the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory started in 1992 to measure CO2 and other trace gases on tall television transmission towers [Bakwin et al., 1995]. An essential question in connection with these tower measurements is the area around the tower from which fluxes substantially contribute to the observed short‐term variability of trace gas mixing ratios. We present here a simple data and back trajectory‐based method to estimate the fraction of the observed short‐term variability explained by a localized flux around a tall television transmission tower in Wisconsin in dependence of its location relative to the tower (the concentration “footprint”). We find that the timescale over which the imprint of surface fluxes on air parcels before its arrival at the tower are still discernible in the mixing ratio variations observed at the tower is of the order of 1.5 days. Based on this timescale and the characteristics of air parcel trajectories, we infer a spatial extent of the footprint of the order of 106 km2, or roughly a tenth of the area of the United States. This is encouraging evidence that tall tower measurements may be useful in global inversions and may also have implications for monitoring fluxes of anthropogenic trace substances on regional scales.

Water vapor density effect on measurements of trace gas mixing ratio and flux with a massflow controller

One configuration in measurements of trace species in the atmosphere uses a massflow controller to regulate airflow through a device that traps the species of interest. Because the flow controller is calibrated with dry air, correction should be made to account for the density effect of water vapor in the ambient air. A common type of massflow controller regulates the flow by measuring temperature difference along a heated tube. It is shown that for these units the true mixing ratio Sc (ratio of mass of trace species c to mass of dry air) is related to the apparent mixing ratio Sc (measurement before correction), as Sc = (1+1.85r)Sc, where r is water vapor mixing ratio of the ambient air, typically varying in the range 0–0.04. Correction should also be made to the surface‐air flux measured with such an apparatus in conjunction with micrometeorological flux gradient or relaxed eddy accumulation method and flux chambers; this involves a correction term proportional to surface evaporation rate and for some measurement configurations the same scale factor (1+1.85r) as for Sc. Examples are given for gaseous mercury to illustrate the magnitude of these corrections. No correction is needed if moisture is removed from the airstream before it enters the massflow controller.

Characterization of the chemical signatures of air masses observed during the PEM experiments over the western Pacific

Extensive observations of tropospheric trace species during the second NASA Global Tropospheric Experiment Western Pacific Exploratory Mission (PEM‐West B) in February‐March 1994 showed significant seasonal variability in comparison with the first mission (PEM‐West A), conducted in September‐October 1991. In this study we adopt a previously established analytical method, i.e., the ratio C2H2/CO as a measure of the relative degree of atmospheric processing, to elucidate the key similarities and variations between the two missions. In addition, the C2H2/CO ratio scheme is combined with the back‐trajectory‐based and the LIDAR‐based air mass classification schemes, respectively, to make in‐depth analysis of the seasonal variation between PEM‐West A and PEM‐West B (hereinafter referred to as PEM‐WA and PEM‐WB). A large number of compounds, including long‐lived NMHCs, CH4, and CO2, are, as expected, well correlated with the ratio C2H2/CO. In comparison with PEM‐WA, a significantly larger range of observed C2H2/CO values at the high end for the PEM‐WB period indicates that the western Pacific was more impacted by “fresher” source emissions, i.e., faster or more efficient continental outflow. As in the case of PEM‐WA, the C2H2/CO scheme complements the back‐trajectory air mass classification scheme very well. By combining the two schemes, we found that the atmospheric processing in the region is dominated by atmospheric mixing for the trace species analyzed. This PEM‐WB wintertime result is similar to that found in PEM‐WA for the autumn. In both cases, photochemical reactions are found to play a significant role in determining the background mixing ratios of trace gases, and in this way the two processes are directly related and dependent upon each other. This analysis also indicates that many of the upper tropospheric air masses encountered over the western Pacific during PEM‐WB may have had little impact from eastern Asia's continental surface sources. NOx mixing ratios were significantly enhanced during PEM‐WB when compared with PEM‐WA, in the upper troposphere's more atmospherically processed air masses. These high levels of NOx resulted in a substantial amount of photochemical production of O3. A lack of corresponding enhancements in surface emission tracers strongly implies that in situ atmospheric sources such as lightning are responsible for the enhanced upper tropospheric NOx. The similarity in NOx values between the northern (higher air traffic) and southern continental air masses together with the indications of a large seasonal shift suggests that aircraft emissions are not the dominant source. However, photochemical recycling cannot be ruled out as this in situ source of NOx.

Trace gas mixing ratio variability versus lifetime in the troposphere and stratosphere: Observations

Several archived data sets have been reviewed to examine the relationship between mixing ratio variability and lifetime for hydrocarbon and halocarbon species in the troposphere and stratosphere. The dependence on lifetime was described by the power law relationship slnX = Aτ−b where slnX is the standard deviation of the ln of the mixing ratios, A is a proportionality coefficient, and b is an exponent that relates to the dominance of sink terms in the regional variability budget. At the Harvard forest ground site, winter and summer data displayed the same lifetime dependence, τ−0.18, which was significantly weaker than the τ−0.5 dependence of remote tropospheric data, indicating that source terms dominated regional variability at Harvard. In addition, the ratio of summer to winter slnX values was found to be similar for all species except ethane, averaging 1.54±0.04. This ratio is consistent with a factor of 11 seasonal change in the species lifetimes, given a τ−0.18 lifetime dependence. Stratospheric data displayed a stronger lifetime dependence than tropospheric trends, indicating a more dominant role for sink terms in describing spatial variability in this region of the atmosphere. We show that a unique power law relationship between slnX ratios for two species Xi and Xj and the kinetic slope of ln(Xi) versus ln lpar;Xj) correlation plots is found to hold in both observations and theory. Thus knowledge of the coefficient b allows for a clearer understanding of the relationship between observed slopes of ln (Xi) versus ln (Xj) correlation plots and the ratio of the species lifetimes.

Reconstructing recent atmospheric trace gas concentrations from polar firn and bubbly ice data by inverse methods

We present a method to extract the atmospheric signal of trace gas mixing ratios from firn and bubbly ice measurements. This method, validated using data from Antarctic sites (Vostok and DE08), includes a numerical model that simulates air transport in the firn, and inverse theory. We focus here on atmospheric CH4 reconstruction, but the method can be used to reconstruct recent changes in any trace gas elemental or isotopic composition measured in firn and ice, that has no chemical interaction with solid H2O. This study also provides useful information on the effective diffusity‐porosity relationship and quantifies the smoothing effect due to gas diffusion in firn and at pore closure, showing the typical time periods of events that are filtered by the firn and therefore not observed in the gas record of ice cores.

Mass fluxes of O3, CH4, N2O and CF2Cl2 in the lower stratosphere calculated from observational data

Trace gas mixing ratio data from the Upper Atmosphere Research Satellite (UARS) are combined with a radiatively derived transformed Eulerian mean (TEM) stream function to estimate the net ozone (O3) mass flux from the stratosphere to the troposphere and to investigate the net fluxes of methane (CH4), nitrous oxide (N2O), and CFC‐12 (CF2Cl2) into the lower stratosphere. The mass fluxes of ozone and long‐lived tracers such as nitrous oxide, methane, and CFC‐12 in the lower stratosphere can be estimated from data obtained by the cryogenic limb array etalon spectrometer (CLAES), the microwave limb sounder (MLS) for ozone, and the Halogen Occultation Experiment (HALOE) for ozone and methane. The flux of ozone from the stratosphere to the troposphere is estimated to be 510 Tg of ozone per year with a range of 450 to 590 Tg O3/yr. Net fluxes into the stratosphere are estimated as 27 Tg of methane per year, 8 Tg/yr of N in nitrous oxide, and 0.08 Tg/yr of CF2Cl2. There is good agreement with previous estimates within the range of uncertainty of these calculations.

Behavior of trace gas mixing ratios on a very tall tower in North Carolina

We present a 15‐month record of mixing ratios of CO, CH4, N2O, and eight halogenated gases (CCl3F, CCl2F2, CCl2FCClF2, CH3CCl3, CCl4, CHCl3, C2Cl4, and SF6) at a rural site in eastern North Carolina. The data result from hourly gas Chromatographic analyses of air sampled at three heights on a 610‐m‐tall telecommunications tower during November 1994 through January 1996. At night, most of these gases were more abundant near the ground (51 m) than aloft (496 m) because of the buildup of local and regional surface emissions in the shallow nocturnal stable layer. The abundance and variability of trace gases at this continental site were generally higher than those at similar latitude remote locations. Mixing ratios of most gases were well correlated in polluted air masses occasionally advected to the tower. Frequent, strong enhancements in CHCl3 at the lower sampling level(s) indicate a local point source(s) of this gas that is not associated with combustion. Temporal trends of regional background mixing ratios at this continental site are, for the most part, in good agreement with recent trends of remote background mixing ratios in the northern hemisphere.

A feasible Global Carbon Cycle Observing System: a plan to decipher today's carbon cycle based on observations

AbstractA design is presented to continuously monitor the transfers of carbon between the atmosphere and the terrestrial biosphere and oceans on large spatial scales. A consideration of the expected signal‐to‐noise suggests that a very cost effective method is to perform repeated measurements of the mixing ratios of trace gases in the atmospheric column at an increased number of sites compared to the present geographical coverage. This can be accomplished with existing technology, provided that more automation is applied to the sampling process as well as to the analytical procedures. The resulting data will be crucial to test extrapolations based on direct flux measurements to regional and global scales.