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NASA NTRS1992

Distribution of tropospheric ozone in the tropics from satellite and ozonesonde measurements

Measurements from two independent satellite data sets have been used to derive the climatology of the integrated amount of ozone in the troposphere. These data have led to the finding that large amounts of ozone pollution are generated by anthropogenic activity originating from both the industrialized regions of the Northern Hemisphere and from the southern tropical regions of Africa. To verify the existence of this ozone anomaly over this region of the world, an ozonesonde capability has been established at Ascension Island, located downwind of the primary source region of this ozone pollution, which likely results from the photochemical oxidation of emissions emanating from the widespread burning of savanna. These first ozonesonde profiles suggest that much of the ozone generated over Africa during the 'burning season' (primarily July-October) reaches Ascension Island. These high levels of ozone in the lower troposphere become much lower by December. Elevated ozone concentrations in the middle troposphere are once again evident in February, which may be the result of biomass burning emissions being transported from western and northern Africa.

Fishman, J.↗

NASA NTRS1992

Distribution of tropospheric ozone at Brazzaville, Congo, determined from ozonesonde measurements

An analysis of 33 ozonesonde launches in Brazzaville, Congo (4 deg S, 15 deg E), between June 1990 and May 1991 is presented. The data indicate highest tropospheric amounts between June and early October, coincident with the dry season and with the presence of enhanced widespread biomass burning. The seasonal cycle of ozone derived from the ozonesonde measurements is in good agreement with the climatological seasonal cycle inferred from the use of satellite data amd both seasonal cycles peak in September. Averaged throughout the year, the integrated amount of ozone derived from the ozonesondes is 44 Dobson units (DU) and is 39 DU using the satellite data. Within the troposphere the highest partial pressures are generally found at pressure levels near 700 mbar (about 3 km). Using simultaneous ozonesonde data from Ascension Island (8 deg S, 15 deg W), examples are presented illustrating that differences in the troposphere are primarily responsible for the observed spatial gradients of total ozone observed by TOMS.

Cros, Bernard↗

NASA NTRS1991

Tropospheric processes: Observations and interpretation

Three aspects of tropospheric chemical processes imposed by manmade emission of source gases will be discussed. First, the implications for the OH distribution and thereby for the lifetime of source gases which are controlled by reactions with OH in the troposphere (e.g., CH4 and HCFC) are investigated. This is of importance for stratosphere ozone and climate. Second, we will study the impact of source gas emission on tropospheric ozone and discuss the possibility to estimate indirect climate effects from the changes in ozone and other climate gases. Finally, the degradation of HFC and HCFC's is discussed.

Isaksen, Ivar S. A.↗

NASA NTRS1992

Tropospheric ozone and aerosol observations - The Alaskan Arctic

This paper discusses in situ measurements of O3, aerosol number density, and aerosol size obtained during NASA Arctic Boundary Layer Expedition aircraft flights over the Alaskan Arctic region. The major source of summer O3 for the troposphere in the intrusion of stratospheric air and subsequent transport to lower altitudes. Photochemistry of mixed layer emissions and O3 transported from high northern latitude urban/industrialized areas do not appear to play major roles as sources of O3 for the Alaska region. O3 gradients reflect the loss at the surface and supply from the stratosphere. Free tropospheric O3 averaged 74 ppbv compared to 32 ppbv for the mixed layer. O3 loss mechanisms are a combination of the destruction via photochemistry, chemical reaction with surface emissions, and direct loss through deposition to the surface. The boreal forest in the most efficient of the O3 sinks and has the largest increase in aerosol number density relative to the free troposphere.

Gregory, Gerald L.↗

NASA NTRS1992

Summertime tropospheric observations related to N(x)O(y) distributions and partitioning over Alaska - Arctic Boundary Layer Expedition 3A

Measurements of NO, NO2, PAN and NO(y) are presented for the summertime middle/lower troposphere over northern high latitudes. Chemical signatures from concurrent measurements of O3, CO, C2H2, C2H6, C3H8, C2Cl4, and H2O are used to characterize factors affecting the budget and distribution of N(x)O(y) in the Arctic and Sub-Arctic tropospheric air masses sampled over Alaska during the NASA Arctic Boundary Layer Expedition (ABLE 3A). The results implicate biomass burning in Siberia as the probable source of about one-third of the NO(y) abundance within the middle lower troposphere over Alaska and the downward transport of air from altitude in the vicinity of the tropopause as a major contributor to the abundance of NO(y) within the lower 6 km column over Alaska.

Sandholm, S. T.↗

NASA NTRS1991

Tropospheric Emission Spectrometer for the Earth Observing System

A Tropospheric Emission Spectrometer (TES) for the Earth Observing System (EOS) series of polar-orbiting platforms is described. TES is aimed at studying tropospheric chemistry, in particular, the exchange of gases between the surface and the atmosphere, urban and regional pollution, acid rain precursors, sources and sinks of greenhouse gases, and the interchange of gases between the troposphere and the stratosphere. TES is a high-resolution (0.025/cm) infrared Fourier transform spectrometer operating in the passive thermal-emission mode in a very wide spectral range (600 to 4350/cm; 2.3 to 16.7 microns). TES has 32 spatial pixels in each of four optically conjugated linear detector arrays, each optimized for a different spectral region.

Glavich, Thomas A.↗

NASA NTRS1993

Upper tropospheric ozone production following mesoscale convection during STEP/EMEX

The chemistry and dynamics of a convective system observed on February 2, 1987 in the EMEX and STEP campaigns are analyzed. Chemical and thermodynamic profiles in undisturbed air near the EMEX 9 system indicate that the troposphere was well mixed by previous convection. As a consequence there was little direct transport from the boundary layer to the upper troposphere and air transported upward was detrained throughout the middle and upper troposphere. There was minimal effect on O3 production. Other convective complexes located 800-900 km upstream produced greater perturbations on trace gas profile immediately below the tropopause. Ozone production was reduced by about 0.25 ppbv/d at these altitudes, representing a reduction in P(O3) of 15-20 percent over the column from 14.5 to 17 km. P(O3) from 12 to 17 km in a region distant from active convection and subject to lightning was 2-3 times higher than it would have been without lightning.

Pickering, Kenneth E.↗

NASA NTRS1987

Tropospheric ozone from satellite total ozone measurements

A method for determining the amount of ozone in the tropical troposphere from concurrent sets of satellite data is presented. This procedure is applied only in the Tropics and the results indicate that a significant longitudinal gradient is present at low latitudes and that the highest amounts of tropospheric ozone are located west (i.e., downwind) of Africa and South America. Such a distribution suggests that biomass burning, or another stationary source of continental origin, is the largest source of ozone in the Tropics. The integrated amount of ozone in the Tropics that is derived from this analysis is comparable to or only slightly less than the amount of ozone that is present in northern mid latitudes. If such an interpretation is valid, then it suggests that the magnitude of the amount of tropospheric ozone resulting from in situ photochemical production in this region is comparable to the in situ photochemical source from industrialized emissions.

Fishman, Jack↗

NASA NTRS1993

Radio metric errors due to mismatch and offset between a DSN antenna beam and the beam of a troposphere calibration instrument

Two components of the error of a troposphere calibration measurement were quantified by theoretical calculations. The first component is a beam mismatch error, which occurs when the calibration instrument senses a conical volume different from the cylindrical volume sampled by a Deep Space Network (DSN) antenna. The second component is a beam offset error, which occurs if the calibration instrument is not mounted on the axis of the DSN antenna. These two error sources were calculated for both delay (e.g., VLBI) and delay rate (e.g., Doppler) measurements. The beam mismatch error for both delay and delay rate drops rapidly as the beamwidth of the troposphere calibration instrument (e.g., a water vapor radiometer or an infrared Fourier transform spectrometer) is reduced. At a 10-deg elevation angle, the instantaneous beam mismatch error is 1.0 mm for a 6-deg beamwidth and 0.09 mm for a 0.5-deg beam (these are the full angular widths of a circular beam with uniform gain out to a sharp cutoff). Time averaging for 60-100 sec will reduce these errors by factors of 1.2-2.2. At a 20-deg elevation angle, the lower limit for current Doppler observations, the beam-mismatch delay rate error is an Allan standard deviation over 100 sec of 1.1 x 10(exp -14) with a 4-deg beam and 1.3 x 10(exp -l5) for a 0.5-deg beam. A 50-m beam offset would result in a fairly modest (compared to other expected error sources) delay error (less than or equal to 0.3 mm for 60-sec integrations at any elevation angle is greater than or equal to 6 deg). However, the same offset would cause a large error in delay rate measurements (e.g., an Allan standard deviation of 1.2 x 10(exp -14) over 100 sec at a 20-deg elevation angle), which would dominate over other known error sources if the beamwidth is 2 deg or smaller. An on-axis location is essential for accurate troposphere calibration of delay rate measurements. A half-power beamwidth (for a beam with a tapered gain profile) of 1.2 deg or smaller is desired for calibration of all types of radio metrics. A water-vapor radiometer calibration beam of this size with very low sidelobes would require a clear aperture antenna with a diameter of at least 1.5 m if the primary water vapor sensing channel were in the 20-22 GHz range.

R P Linfield↗

NASA NTRS1994

Absolute determination of local tropospheric OH concentrations

Long path absorption (LPA) according to Lambert Beer's law is a method to determine absolute concentrations of trace gases such as tropospheric OH. We have developed a LPA instrument which is based on a rapid tuning of the light source which is a frequency doubled dye laser. The laser is tuned across two or three OH absorption features around 308 nm with a scanning speed of 0.07 cm(exp -1)/microsecond and a repetition rate of 1.3 kHz. This high scanning speed greatly reduces the fluctuation of the light intensity caused by the atmosphere. To obtain the required high sensitivity the laser output power is additionally made constant and stabilized by an electro-optical modulator. The present sensitivity is of the order of a few times 10(exp 5) OH per cm(exp 3) for an acquisition time of a minute and an absorption path length of only 1200 meters so that a folding of the optical path in a multireflection cell was possible leading to a lateral dimension of the cell of a few meters. This allows local measurements to be made. Tropospheric measurements have been carried out in 1991 resulting in the determination of OH diurnal variation at specific days in late summer. Comparison with model calculations have been made. Interferences are mainly due to SO2 absorption. The problem of OH self generation in the multireflection cell is of minor extent. This could be shown by using different experimental methods. The minimum-maximum signal to noise ratio is about 8 x 10(exp -4) for a single scan. Due to the small size of the absorption cell the realization of an open air laboratory is possible in which by use of an additional UV light source or by additional fluxes of trace gases the chemistry can be changed under controlled conditions allowing kinetic studies of tropospheric photochemistry to be made in open air.

Armerding, Wolfgang↗

NASA NTRS1993

MOPITT - A gas correlation spectrometer for tropospheric Earth observations

MOPITT (Measurement of Pollution in the Troposphere) is an instrument that will fly on the EOS AM-1 Polar Orbiting Platform, to be launched in mid-1998. The instrument accurately measures the concentration of carbon monoxide (CO) and methane (CH4) gas in the troposphere, using novel and conventional gas correlation spectroscopy techniques. These techniques are used to measure both the column amount and the vertical profile of the two gases in the troposphere. The instrument is nadir viewing and has cross-track scanning ability. It measures upwelling IR radiation through the atmosphere in the 4.6-micron and 2.3-micron bands for CO detection, and 2.2-micron for CH4. The instrument performance is enhanced using Stirling cycle mechanical coolers to maintain the IR detectors at less than 100 K. MOPITT has a total of eight detector channels to measure the total column of atmospheric CH4 gas to a precision of 1 percent, and to measure CO profiles to a precision of 10 percent. The instrument is self-calibrating to ensure data validity using internal targets and an external cold space view.

Drummond, James R.↗

NASA NTRS1994

Tropospheric ozone in the western Pacific Rim: Analysis of satellite and surface-based observations along with comprehensive 3-D model simulations

Tropospheric ozone production and transport in mid-latitude eastern Asia is studied. Data analysis of surface-based ozone measurements in Japan and satellite-based tropospheric column measurements of the entire western Pacific Rim are combined with results from three-dimensional model simulations to investigate the diurnal, seasonal and long-term variations of ozone in this region. Surface ozone measurements from Japan show distinct seasonal variation with a spring peak and summer minimum. Satellite studies of the entire tropospheric column of ozone show high concentrations in both the spring and summer seasons. Finally, preliminary model simulation studies show good agreement with observed values.

Young, Sun-Woo↗

NASA NTRS1994

Direct measurements of tropospheric ozone using TOMS data

Fishman and Larsen have proposed a new algorithm, called 'tropospheric residual method,' which retrieves the climatological tropospheric ozone by using SAGE (Stratospheric Aerosol and Gas Experiment) and TOMS (Total Ozone Mapping Spectrometer) data. In this paper, we will examine the feasibility of detection for tropospheric ozone using only TOMS data. From a case study over the Atlantic Ocean off the coast of west Africa, it has been found that total ozone in the archived TOMS data has been overestimated over a region of marine-stratocumulus clouds.

Hudson, Robert D.↗

NASA NTRS1994

Use of radon and cosmogenic radionuclides as indicators of exchange between troposphere and stratosphere

This research grant covered participation in the operational phase of NASA's Stratosphere-Troposphere Exchange Project (STEP), a multi-agency airborne science program conducted aboard NASA U-2 and ER-2 high altitude research aircraft. The primary goals of STEP were to investigate the mechanisms of irreversible movement of mass, trace gases, and aerosols from the troposphere into the stratosphere, and to explain the observed dryness of the stratosphere. Three flight experiments were conducted to address these questions: two extratropical experiments, in 1984 and 1986, and a tropical experiment, in 1987. The cosmogenic radionuclides Be-7 and P-32, produced in the stratosphere by cosmic rays, and Rn-222 (radon), emitted from continental soils, were well-suited as tracers of intra-stratospheric air mass movements, and to follow episodes of troposphere to stratosphere exchange. Measurements of Be-7 and P-32 were made in all three STEP experiments. Measurements of radon were made in the tropical experiment only. The equipment worked well, and produced a valuable data set in support of the STEP objectives, as indicated by the 'quick-look' results outlined.

Kritz, Mark A.↗

NASA NTRS1994

A Monte Carlo study of photochemical model uncertainties affecting the calculation of subsonic perturbations in the upper troposphere

Monte Carlo methods are frequently applied to the evaluation of uncertainties in models with multiple inputs that themselves have associated imprecisions. In the case of photochemical models used to evaluate changes in O3 or OH, inputs analyzed include rate coefficients measured in the laboratory, and chemical and physical constituents measured in the atmosphere. The Monte Carlo method was used with the 1-dimensional GSFC tropospheric photochemical model to examine uncertainty propagation to calculation of NO(x) and the major oxidants (O3, OH) in the upper troposphere. In all cases chemical kinetics inputs are varied and the NO(x) perturbation of a subsonic fleet is simulated. A series of model runs is used to explore sensitivities of model-computed parameters to other parameters: heterogeneous processes, the uncertainty in upper tropospheric H2O vapor measurements, aircraft emissions at different latitudes.

Thompson, Anne M.↗

NASA NTRS1995

Study of tropospheric correction for intercontinental GPS common-view time transfer

Current practice is to incorporate general empirical models of the troposphere, which depend only on the station height and the elevation of the satellite, in GPS time receivers used for common-view time transfer. Comparisons of these models with a semi-empirical model based on weather measurements show differences of several nanoseconds. This paper reports on a study of tropospheric correction during GPS common-view time transfer over a short baseline of about 700 km, and three long baselines of 6400 km, 9000 km and 9600 km. It is shown that the use of a general empirical model of the troposphere within a region where the climate is similar does not affect time transfer by more than a few hundreds of picoseconds. For the long distance links, differences between the use of a general empirical model and the use of a semi-empirical model reach several nanoseconds.

Lewandowski, Wlodzimierz W.↗

NASA NTRS1994

Low to middle tropospheric profiles and biosphere/troposphere fluxes of acidic gases in the summertime Canadian taiga

We report features of acidic gases in the troposphere from 9 to 5000 m altitude above ground over the Canadian taiga in the summer of 1990. The measurements were conducted at a 30-m meteorological tower and from the NASA Wallops Electra aircraft as part of the joint U.S.-Canadian Arctic Boundary Layer Expedition (ABLE) 3B Northern Wetland Studies (NOWES). We sampled air for acidic gases using the mist chamber collector coupled with subsequent analysis using ion chromatography. At the tower we collected samples at two heights during a 13-day period, including diurnal studies. Using eddy flux and profile data, we estimated the biosphere/troposphere fluxes of nitric, formic, and acetic acids and sulfur dioxide. For the organic acids, emissions from the taiga in the afternoon hours and deposition during the predawn morning hours were observed. The flux intensities alone were however not high enough to explain the observed changes in mixing ratios. The measured deposition fluxes of nitric acid were high enough to have a significant influence on its mixing ratio in the boundary layer. On three days we measured vertical profiles of nitric, formic, and acetic acids through the lower to midtroposphere. We found that the chemical composition of the troposphere was extremely heterogenous. Pronounced layers of polluted air were readily apparent from our measurements. Local photochemical production and episodic long-range transport of trace components, originating from biomass burning and possibly industrial emissions, appear to have a strong influence on the composition of the troposphere and biosphere/troposphere fluxes of acidic gases at this site.

Klemm, O.↗

NASA NTRS1994

Summertime tropospheric ozone distributions over central and eastern Canada

Ozone measurements were obtained between the surface and the 6-km altitude on aircraft flights over central and eastern Canada during the summer 1990 NASA Global Tropospheric Experiment Arctic Boundary Layer Expedition (GTE/ABLE 3B). Tropospheric O3 budgets for these regions were observed to be highly variable and significantly impacted by long-range transport and regional scale air mass modification processes. For example, integrated O3 abundance below 5-km altitude averaged 40% and 30% greater in air masses influenced by anthropogenic sources and biomass burning, respectively, than in background (polar) air. Conversely, aged air transported from subtropical areas of the Pacific at times reduced O3 abundance in this height interval by up to 20%. Though intrusion of anthropogenic air was infrequent during the experiment period, the influence of biomass-burning emissions was particularly notable as two thirds of the flights sampled air influenced by plumes from fires burning in Alaska and western Canada. The impinging pollution, both natural and anthropogenic, not only elevated O3 levels directly but also was a source of reactive nitrogen (and nonmethane hydrocarbons) which generally increases the tropospheric lifetime of O3 via moderation of photochemical destruction rates.

Anderson, B. E.↗