bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of parameterized nitric acid rainout rates using a coupled stochastic‐photochemical tropospheric model
Authors: Stewart Richard W. , Thompson Anne M. , Owens Melody A. , Herwehe Jerold A.
Published: February 2008

A major tropospheric loss of soluble species such as nitric acid (HNO3) results from scavenging by water droplets. Several theoretical formulations have been advanced which relate an effective time independent loss rate for soluble species to statistical properties of precipitation such as the wet fraction and length of a precipitation cycle. There is not enough data available on trace species concentrations to test the computational results of alternative loss rate models against observations. Therefore in this paper, various “effective” loss rates that have been proposed are compared with the results of detailed time dependent model calculations carried out over a seasonal time scale. The model which we have developed for this purpose is a stochastic precipitation model coupled to a tropospheric photochemical model. The results of numerous time dependent seasonal model runs are used to derive numerical values for the nitric acid residence time for several assumed sets of precipitation statistics. These values are then compared with the results obtained by utilizing theoretical “effective” loss rates in time independent models.
An intercomparison of measurement systems for vapor and particulate phase concentrations of formic and acetic acids
Authors: Keene William C. , Talbot Robert W. , Andreae Meinrat O. , Beecher Kristene , Berresheim Harold , Castro Mark , Farmer J. Carl , Galloway James N. , Hoffmann Michael R. , Li Shao‐Meng , Maben John R. , Munger J. William , Norton Richard B. , Pszenny Alexander A. P. , Puxbaum Hans , Westberg Hal , Winiwarter Wilfried
Published: February 2008

During June 1986, eight systems for measuring vapor phase and four for measuring particulate phase concentrations of formic acid (HCOOH) and acetic acid (CH3COOH) were intercompared in central Virginia. HCOOH and CH3COOH vapors were sampled by condensate, mist, Chromosorb 103 GC resin, NaOH‐coated annular denuders, NaOH impregnated quartz filters, K2CO3 and Na2CO3 impregnated cellulose filters, and Nylasorb membranes. Atmospheric aerosol was collected on Teflon and Nuclepore filters using both hi‐vol and lo‐vol systems to measure particulate phase concentrations. Samples were collected during 31 discrete day and night intervals of 0.5–2 hour duration over a 4‐day period. Performance of the mist chamber and K2CO3 impregnated filter techniques were also evaluated using zero air and ambient air spiked with HCOOHg, CH3COOHg, and formaldehyde (CH2Og) from permeation sources. Results of this intercomparison show significant systematic and episodic artifacts among many currently deployed measurement systems for HCOOHg and CH3COOHg. The spiking experiments revealed no significant interferences for the mist chamber technique and results generated by the mist chamber and denuder techniques were statistically indistinguishable. The condensate technique showed general agreement with the mist chamber and denuder methods, but episodic bias between these systems was inferred from large and significant differences observed during the first day of sampling. Nylasorb membranes are unacceptable for collecting carboxylic acid vapors as they did not retain HCOOHg and CH3COOHg quantitatively. Strong base impregnated filter and GC resin sampling techniques are prone to large positive interferences apparently resulting, in part, from reactions involving CH2Og to generate HCOOH and CH3COOH subsequent to collection. Significant bias presumably associated with differences in postcollection handling was observed for particulate phase measurements by participating groups. Analytical bias did not contribute significantly to differences in vapor and particulate phase measurements.
SAGE II aerosol validation: Selected altitude measurements, including particle micromeasurements
Authors: Oberbeck Verne R. , Livingston John M. , Russell Philip B. , Pueschel Rudolf F. , Rosen James N. , Osborn Mary T. , Kritz Mark A. , Snetsinger Kenneth G. , Ferry Guy V.
Published: February 2008

Correlative aerosol measurements taken at a limited number of altitudes during coordinated field experiments are used to test the validity of particulate extinction coefficients derived from limb path solar radiance measurements taken by the Stratospheric Aerosol and Gas Experiment (SAGE) II Sun photometer. In particular, results are presented from correlative measurement missions that were conducted during January 1985, August 1985, and July 1986. Correlative sensors included impactors, laser spectrometers, and filter samplers aboard a U‐2 airplane, an upward pointing lidar aboard a P‐3 airplane, and balloon‐borne optical particle counters (dustsondes). The main body of this paper focuses on the July 29, 1986, validation experiment, which minimized the many difficulties (e.g., spatial and temporal inhomogeneities, imperfect coincidences) that can complicate the validation process. On this day, correlative aerosol measurements taken at an altitude of 20.5 km agreed with each other within their respective uncertainties, and particulate extinction values calculated at SAGE II wavelengths from these measurements validated corresponding SAGE II values. Additional validation efforts on days when measurement and logistical conditions were much less favorable for validation are discussed in an appendix.
Validation of SAGE II ozone measurements
Authors: Cunnold D. M. , Chu W. P. , Barnes R. A. , McCormick M. P. , Veiga R. E.
Published: February 2008

The error budget of the Stratospheric Aerosol and Gas Experiment (SAGE) II ozone profile measurements is discussed in depth. Five ozone profiles are compared against coincident ROCOZ‐A and electrochemical concentration cell (ECC) ozonesonde measurements at Natal, Brazil (6°S) and Wallops Island, Virginia (36°N). The mean difference between all the measurements is approximately 1% and the agreement is within 7% at all altitudes between 20 and 53 km. Using datasonde and National Weather Service satellite observations of temperature, the agreement is almost equally as good for ozone mixing ratios on pressure surfaces. A comparison of the intrinsic SAGE II measurement errors with measured tropical variances suggests that the precision of the ozone profiles is approximately 5% between 24 and 36 km, degrading to 7% at an altitude of 48 km. It is inferred that the measurement errors possess a vertical correlation distance of 3 km and that therefore the profile precision improves by a factor of approximately 1.3 if the profiles were to be smoothed over 5 km vertically. The repeatability of SAGE II ozone profiles depends also upon the uncertainty in the profiles' reference altitudes. These errors are correlated over 7‐day periods and increase to 200 m over that period of time. The accuracy of SAGE II ozone profiles is expected to be 6% above 25 km altitude. The SAGE II profiles provide useful ozone information up to approximately 60 km altitude and are more precise than the SAGE I profiles. SAGE II profiles, combined with revised SAGE I profiles, form an excellent data base for estimating the long‐term trend in stratospheric ozone since 1979.
Water vapor and methane in the upper stratosphere: An examination of some of the Nimbus 7 measurements
Authors: Hansen Anthony R. , Robinson G. D.
Published: February 2008

An investigation of the zonal mean volume mixing ratios of water vapor and methane from January through May 1979, derived from the Nimbus 7 limb infrared monitor of the stratosphere (LIMS) and stratosphere and mesosphere sounder (SAMS) experiments is undertaken with the objective of inferring the water vapor mixing ratio of air that enters the stratosphere from the troposphere and, concomitantly, the yield of water vapor from photochemical oxidation of methane in the stratosphere. The results are necessarily imprecise owing to a high level of random error in the data (estimated to be roughly 15–20% for methane and 5% for water vapor) and possible systematic errors of unknown magnitude. However, the results are generally consistent with chemical/dynamical modeling by other workers. The water vapor yield averaged between 1.5 and 2.0, although variability with time and level was relatively large. Water vapor yield more consistent with model results was obtained when only nighttime LIMS data were used. The general indication is that the water vapor yield increases with height in the 16‐ to 3‐mbar layer. It appears that the average water vapor mixing ratio of air entering the stratosphere during the period studied was ∼3.25×10−6. Possible implications of these results to the stratosphere‐troposphere mass exchange problem are discussed.
The flux of radon and thoron from Australian soils
Authors: Schery S. D. , Whittlestone S. , Hart K. P. , Hill S. E.
Published: February 2008

The accumulator technique was used to measure radon and thoron flux density at a variety of locations throughout Australia. This is the first such systematic study of Australia and, in the case of thoron, one of few such studies of any large land mass. Seasonally adjusted arithmetic mean flux densities from Australian soils were estimated to be 22 mBq m−2 s−1 (1.05 atom cm−2 s−1) for radon and 1.7 Bq m−2 s−1 (0.0135 atom cm−2 s−1) for thoron. Consideration of statistical sampling error, and systematic error with the accumulator method, leads to an error estimate of about ±20% for these numbers; projection of total flux to the atmosphere requires consideration of additional sources of error. Only modest correlations with variables easily measured in the field were observed. The strongest correlation was a positive one between flux density and gamma dose rate 1 m above ground. Weaker correlations were seen with soil temperature (positive) and soil moisture (negative at higher moistures). Radon and thoron flux density were strongly correlated, but only a weak correlation (negative) existed between them and vegetation. The amount of radon isotope released to the pore space seems particularly important for controlling the wide variation in observed flux densities, but it remains difficult to predict flux densities based on simple field measurements or information in conventional soil and geological maps.
Cloud overlap statistics
Authors: Tian Lin , Curry Judith A.
Published: February 2008

The U.S. Air Force Three‐Dimensional Nephanalysis (3DNEPH) has been employed to analyze the vertical distribution of clouds and cloud overlap statistics during January 1979 over the north Atlantic Ocean (40° to 60°N). The 3DNEPH integrates both satellite and conventional observations and gives what is probably the best available information on the vertical distribution of clouds. This region was chosen because of the predominance of layered clouds and the high density of conventional observations. The grid size of the 3DNEPH is ∼45 km, and the data set was additionally averaged over three different grid sizes: 90, 221, and 442 km. Three cloud overlap assumptions that have been commonly used were tested, namely the maximum, minimum, and random overlap assumptions. For adjacent layers of the 3DNEPH that contained cloud the maximum overlap assumption performed the best, accurately determining the total cloud cover to within the roundoff error for the layered cloud amounts in 82% of the cases. For two or three cloud layers that were separated by clear interstices the random overlap assumption performed the best overall for all resolutions, although there were systematic biases in the predicted cloud fraction which depend on the cloud fraction of the layers and on grid size. For grid sizes ≥9O km, random overlap resulted in a systematic underestimation of total cloud cover, ∼5%. Random overlap performed worst when there were two layers with intermediate cloud fractions (30–70%). The results of this study indicate that while random overlap performs reasonably well on average, the systematic bias (which depends on grid resolution) and random discrepancies could result in significant errors when this approximation is used in general circulation modeling and cloud climatologies.
Some aspects of stratospheric electric fields due to a constant convection cuurent density‐charge model of cloud structure
Authors: Pinto I. R. C. A. , Pinto O. , Gonzalez W. D.
Published: February 2008

This brief report presents the results of the numeric calculation of the electric field due to positive polarity clouds at balloon altitudes with a constant convection current density (CC) model of charge distribution. For reasonable values of the parameters involved, we show that at horizontal distances larger than approximately 20 km from the top of the cloud, the CC model can give vertical electric fields with similar large magnitudes (volts per meter) in both directions in the stratosphere. We claim that even this simple charge distribution model may explain some “unusual” observed signatures during several events of balloon‐borne electric field measurements reported in the literature, without the necessity to search for more complicated charge distribution models. Another aspect found in association with the CC model is that the ratio between the vertical and horizontal electric fields increases when the balloon drifts away to the cloud. As far as we know, this latter aspect has not been observed in balloon electric field measurements as yet. We suggest that measurements associated with large storms (with tens to hundreds of Coulombs) should be useful for identifying this aspect of the electric field measurements.
Atmospheric depositional characteristics of beryllium 7 and lead 210 along the southeastern Virginia coast
Authors: Todd James F. , Wong George T. F. , Olsen Curtis R. , Larsen Ingvar L.
Published: February 2008

Atmospheric depositional fluxes of 7Be and 210Pb were measured simultaneously in wet‐only and bulk deposition over a 29‐month period (October 1982 through February 1985) in Norfolk, Virginia (36°53′N, 76°18′W). Total precipitation accumulation during 1983 and 1984 was 134 and 129 cm, respectively, slightly above the normal yearly accumulation. The volume‐weighted average concentrations of 7Be in bulk deposition for 1983 and 1984 were 90 and 100 dpm/L, while those for 210Pb were 5.9 and 6.6 dpm/L, respectively. The annual depositional fluxes of 7Be and 210Pb in bulk deposition in 1983 and 1984 were 12.0 and 12.9 dpm/cm2 (for 7Be) and 0.79 and 0.85 dpm/cm2 (for 210Pb), respectively. There was a high degree of correlation between 7Be and 210Pb concentrations in wet‐only deposition. This was not anticipated, considering that the sources of these two radionuclides are different. These results suggest that 7Be and 210Pb cannot be used as two independent tracers for materials originating in the stratosphere versus those from the troposphere. Dry depositional fluxes for both radionuclides, estimated from differences in the wet‐only and bulk fluxes, were calculated to be a maximum of 12 and 11% of the bulk 7Be and 210Pb fluxes, respectively. On an annual average the washout ratio for 7Be in bulk deposition was 370, while that for 210Pb was 215. The annual average total deposition velocities for 7Be and 210Pb were estimated to be 1.3 and 0.7 cm/s, respectively. It is suggested that the apparent differences in the depositional characteristics (that is, total deposition velocity, washout ratio) for these radionuclides are mere artifacts of the manner in which they are calculated and do not necessarily reflect differential behavior in the atmospheric deposition of 7Be and 210Pb.
Anomalous electric fields associated with clouds growing over a source of negative space charge
Authors: Moore C. B. , Vonnegut B. , Holden D. N.
Published: February 2008

Tests of influence mechanism explanations for thundercloud electrification have been attempted by modifying the initial atmospheric electrical conditions beneath some convective clouds. The modification was accomplished by the release of negative space charges into the air from elevated wires connected to a high‐voltage power supply. Anomalous distributions of charge were observed in some clouds with low bases that grew over the charge source. The results of the experiment suggest that influence mechanisms may be operative in the electrification of our mountain clouds and that, normally, the natural, positive space charges in the sub cloud air may initiate the electrification processes.
An investigation of the possible relationships between thundercloud electric fields and the lightning parameters for tall structures
Authors: Chang Jen‐Shih , Beuthe T. G. , Seto L. , Duft A. , Hayashi N. , Chisholm W. , Janischewskyj W.
Published: February 2008

Over the past 10 years the CN Tower in Toronto, Canada (height 553 m above ground level), has provided an excellent opportunity to study the lightning characteristics of tall slender structures. In this work, the statistical relationships between the magnitude of the vertical electric field in the immediate vicinity of the tower and various parameters associated with actual lightning strikes to the tower are presented. These parameters include the flash duration, number of strokes per flash, and interstroke interval times as measured by a video recording system as well as the peak current amplitude, time to peak current, time to half‐tail, total duration, and total charge of each stroke measured using a Rogowski coil. The results show that a significant number of lightning flashes strike the tower in the absence of large electric fields (fields less than 2 kV/m in magnitude). This implies that thunderclouds can be at a considerable distance from the tower during lightning strikes. These “low electric field” strikes are shown to have significantly different characteristics than those which occur during or just after periods of large electrical field activity (large fluctuations and field strengths ≫2 kV/m) when thunderclouds were close to or directly above the tower. The data presented were collected over the time interval from 1978 to 1986.
Electrodynamics of the high‐latitude mesosphere
Authors: Goldberg Richard A.
Published: February 2008

The discovery of apparent large (V/m) electric fields within the mesosphere suggests that this region is more active electrically than originally suspected. High‐latitude observations have been particularly productive in developing new concepts regarding mesospheric electrodynamics. Several high‐latitude observations of large mesospheric fields have been made under both quiet and aurorally active conditions but always below heights where enhanced ionizing radiations could significantly penetrate. Two measurements from Andøya, Norway, have also produced an anticorrelation of horizontal electric field directions with neutral wind velocities, leading to the theoretical description of a newly defined mechanism for V/m electric field generation involving wind‐induced separation of charged aerosols. Evidence for mesospheric aerosols and winds exists at all latitudes but is most evident at high latitudes during the appearance of noctilucent and/or polar mesospheric clouds. New measurements show an influence of such clouds on electric fields mapping downward from the ionosphere, modifying the electric field in both magnitude and direction. Recent results also demonstrate that middle atmospheric electrical parameters can be used to track neutral air turbulence and wave structure at high latitudes, thereby providing a powerful tool for study of mesospheric neutral dynamics and its relationship to the electrodynamic system. This overview concentrates on the various subjects outlined above.
On the diurnal variation of noctilucent clouds
Authors: Jensen Eric , Thomas Gary E. , Toon Owen B.
Published: February 2008

Polar mesospheric clouds (PMC) and noctilucent clouds (NLC) are terms assigned to layers of scattering particles (believed to be water ice) at the cold summertime high‐latitude mesopause. The two types of clouds, believed to be composed of water ice, are clearly related but have been observed under very different circumstances. PMC have been observed by satellites in full daylight, in the afternoon and late morning. NLC are observed from the ground within 2 or 3 hours of local midnight when the sun is below the horizon. We suggest that the differences in their optical properties and in their observed heights can be attributed to a diurnal variation in the properties of a single type of cloud. Using two published models of the diurnal and semidiurnal variations of temperature, vertical wind speed, and eddy diffusion coefficient at high latitude, we simulate the evolution of ice clouds over a 24‐hour period. The microphysical processes of particle genesis, growth, sedimentation, and sublimation are included in our model. We find that the minimum in temperature at about 2000 hours LT causes a sharp maximum in scattered brightness to occur about 1 hour before local midnight, with up to a factor of 7 variation in cloud brightness between noon and midnight. Variations in vertical wind speed and eddy diffusion enhance the variation in cloud brightness, but only slightly. We also find that when the model is adjusted to agree with the observed height for PMC (85 km), it predicts a lower height of about 83 km for ice clouds near midnight, in good agreement with triangulation determinations of NLC heights. These predicted NLC brightness variations may be verified by future ground observations of NLC. However, it will be necessary to make careful corrections for changing illumination and solar extinction conditions throughout the night.
Stratospheric ozone vertical distribution from far‐infrared balloon spectra and statistical analysis of the errors
Authors: Carlotti M. , Barbis A. , Carli B.
Published: February 2008

A daytime and nighttime vertical distribution of ozone is retrieved from far‐infrared emission spectra recorded by a balloon‐borne Fourier transform spectrometer with 0.0033‐cm−1 resolution. The accuracy achieved is approximately 11% in the 27‐ to 39‐km altitude range. The global‐fit analysis performed on several different spectral intervals and on several different limb‐scanning sequences allows a statistical evaluation of individual error components due to frequency‐dependent and time‐dependent uncertainty sources, as well as to spectral noise. The statistical evaluation of the error component due to the latter source is in good agreement with the estimate given by the nonlinear least squares fitting algorithm. The possible causes of the observed 9.5% difference between day and night column densities in the 29‐ to 34‐km altitude range are discussed. Our altitude profiles are compared with the results of previous analyses of the same data set and with the results obtained using other instruments during the same campaign of measurements.
Calibration of the forward scattering spectrometer probe used on the ER‐2 during the Airborne Antarctic Ozone Experiment
Authors: Baumgardner Darrel , Dye James E. , Gandrud Bruce W.
Published: February 2008

The Particle Measuring Systems (PMS) Forward Scattering Spectrometer Probe (FSSP‐100) which was flown on the ER–2 during the Airborne Antarctic Ozone Experiment for the measurement of particles in polar stratospheric clouds has been evaluated and calibrated. The sample volume of the probe per 10‐s sampling period increases from 257 cm3 for 1‐μm particles to 412 for 15‐μm particles, but there is substantial uncertainty in this value. Limitations in the measurements from this instrument and possible corrections are discussed. The uncertainty in the total particle mass measured by the probe may be as large as ± 100%. Recommendations are given for the processing of data from the FSSP used in this project.
Tropospheric ozone in the vicinity of the ozone hole: 1987 Airborne Antarctic Ozone Experiment
Authors: Gregory Gerald L. , Hypes Warren D. , Warren Linda S. , Tuck Adrian F. , Kelly Kenneth K. , Krueger Arlin J.
Published: February 2008

Tropospheric ozone measurements over Antarctica aboard the NASA DC‐8 aircraft are summarized. As part of the August/September 1987 Airborne Antarctic Ozone Experiment, the aircraft flew 13 missions covering a latitude of 53°–90°S, at altitudes to 13 km. Ozone mixing ratios as high as several hundred parts per billion by volume (ppbv) were measured, but in all cases these ratios were observed in pockets or patches of upper atmospheric air. These pockets were observed both in the vicinity of and away from the location of the ozone hole, but they appeared to have occurred with higher frequency near or underneath the ozone hole. At times, and as a result of these pockets, the ozone levels at the flight altitude of the aircraft, as averaged beneath the boundaries of the stratospheric ozone hole, were 2–3 times higher than background tropospheric values. The data suggest that the ozone‐rich air seldom penetrated below about 9‐km altitude. Background ozone values in the surrounding troposphere were typically in the range of 20–50 ppbv. Correlation of tropospheric ozone observations with the boundaries of the ozone hole differed during the experiment. During the early flights (August 28 through September 2), encounters with ozone‐rich air were limited and background tropospheric ozone (at the flight altitude) appeared to decrease beneath the hole. For many of the later flights, and as the hole deepened, the reverse was noted, in that ozone‐rich air was frequently observed in the vicinity of the hole and, as noted earlier, average ozone at the flight altitude was frequently higher than background values.
Surface ozone: Trend details, seasonal variations, and interpretation
Authors: Janach Walter E.
Published: February 2008

Historical data from rural and Alpine sites in Europe and selected recent measurements show how the ozone concentration increased and how its seasonal distributions vary at different locations. The coincidence of the spring maximum at Mauna Loa in Hawaii and at Alpine stations in Europe indicates that the underlying phenomenon affects the entire northern hemisphere. The observed trends and differences between seasonal distributions can be explained with the help of results from recent chemical modeling calculations. Such a heuristic interpretation provides further insight into the processes through which anthropogenic emissions of nitrogen oxides and hydrocarbons influence tropospheric ozone.
Desorption of radon at the Earth's surface
Authors: Schery S. D. , Whittlestone S.
Published: February 2008

Measurements of the sorption coefficient for trace amounts of radon in carrier air were made for a variety of porous materials common at the Earth's surface. The technique used was specific for sorption, so some of the ambiguities in previous studies were avoided. Generally, sorption coefficients decrease significantly with increasing moisture and temperature. Model calculations were carried out to relate the temperature dependence of sorption coefficients to the release of radon to the atmosphere. The time‐dependence of the exhalation depends on the size of the sample, its moisture level, and the rate of propagation of heat into the sample. In the steady state limit for thin samples, there is not necessarily an increase in exhalation with decrease in sorption coefficient. Measurements suggest there could be places on the Earth's surface where desorption of radon is directly important for release of radon to the atmosphere. The top several centimeters of dry, unvegetated soil in arid or semiarid climates, and loose rocks upon such soil, might be situations where desorption is important. However, due to the pervasiveness of moisture in soil in moister climates, and at greater depths in soil, desorption's role is probably limited as a major mechanism for release of radon to the atmosphere over much of the Earth's surface.
Cloud cover analysis with Arctic AVHRR data: 1. Cloud detection
Authors: Key J. , Barry R. G.
Published: February 2008

Automated analyses of satellite radiance data have concentrated heavily on low and middle latitude situations. Some of the design objectives for the International Satellite Cloud Climatology Project (ISCCP) cloud detection procedure such as space and time contrasts are used in a basic algorithm from which a polar cloud detection algorithm is developed. This algorithm is applied to Arctic data for January and July conditions. Both advanced very high resolution radiometer (AVHRR) and scanning multichannel microwave radiometer (SMMR) data are utilized. Synthetic AVHRR and SMMR data for a 7‐day analysis period are also generated to provide a data set with known characteristics on which to test and validate algorithms. Modifications to the basic algorithm for polar conditions include the use of SMMR and SMMR‐derived data sets for the estimation of surface parameters, elimination of the spatial test for the warmest pixel, the use of AVHRR channels 1 (0.7 μm), 3 (3.7 μm), and 4 (11 μm) in the temporal tests and the final multispectral thresholding, and the use of surface class characteristic values when clear‐sky values cannot be obtained. Additionally, the difference between channels 3 and 4 is included in the temporal test for the detection of optically thin cloud. Greatest improvement in computed cloud fraction is realized over snow and ice surfaces; over open water or snow‐free land, all versions perform similarly. Since the inclusion of SMMR for surface analysis and additional spectral channels increases the computational burden, its use may be justified only over snow and ice‐covered regions.
Trace gas emissions from burning Florida wetlands
Authors: Cofer Wesley R. , Levine Joel S. , Winstead Edward L. , LeBel Peter J. , Koller Albert M. , Hinkle C. Ross
Published: February 2008

Measurements of biomass burn‐produced trace gases are presented that were obtained using a helicopter at low altitudes above burning Florida wetlands on November 9, 1987, and from both helicopter and light‐aircraft samplings on November 7, 1988. Carbon dioxide (CO2) normalized emission ratios (ΔX/ΔCO2; V/V; where X is trace gas) for carbon monoxide (CO), hydrogen (H2), methane (CH4), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N2O) were obtained over burning graminoid wetlands consisting primarily of Spartina bakeri and Juncus roemerianus. Some interspersed scrub oak (Quercus spp) and saw palmetto (Screnoa repens) were also burned. No significant differences were observed in the emission ratios determined for these gases from samples collected over flaming, mixed, and smoldering phases of combustion during the 1987 fire. Combustion‐categorized differences in emission ratios were small for the 1988 fire. Combustion efficiency was relatively good (low emission ratios for reduced gases) for both fires. We believe that the consistently low emission ratios were a unique result of graminoid wetlands fires, in which the grasses and rushes (both small‐size fuels) burned rapidly down to standing water and were quickly extinguished. Consequently, the efficiency of the combustion was good and the amount and duration of smoldering combustion was greatly diminished.
Effects of initial active chlorine concentrations on the Antarctic ozone spring depletion
Authors: Henderson G. S. , Evans W. F. J. , McConnell J. C.
Published: February 2008

Several one‐dimensional model experiments have been conducted in order to simulate the observed downward trend of total ozone and the shape of ozone profiles in the Antarctic during the austral spring. The results underline the fact that the O3 depletion is quadratically sensitive to the amount of active chlorine, which we have expressed as the fraction (F) of Clx that is in active form by polar sunrise. For F = 1, this result is largely independent of the occurrence of heterogeneous chemistry after polar sunrise since all of the processing has already occurred. The main O3 loss is due to formation and photolysis of Cl2O2, the mechanism first suggested by Molina et al. [1987]. By comparison, using Brx levels similar to currently measured values, it was found that the BrO + ClO reaction plays a less important role in O3 depletion. The depth of the O3 minimum in spring appears to be related to the vertical extent of the region chemically processed by polar stratospheric clouds as well as the absolute levels of active Clx; more extensive vertical regions result in larger bite outs of the O3 profile. This may account for the difference in O3 minimum between 1986 and 1987. Simulations involving downward vertical transports are unable to reproduce observed decreases in total O3. We speculate that low trace gas mixing ratios of species such as N2O may be remnants of the previous summer and fall conditions, rather than signatures of downward transport during the springtime ozone depletion.
The atmospheric structure during episodes of open cellular convection observed in KonTur 1981
Authors: Kruspe G. , Bakan S.
Published: February 2008

The KonTur (Konvektion und Turbulenz) 1981 experiment was primarily dedicated to the study of organized boundary layer convection. While two research aircraft were used for detailed boundary layer measurements, an aerological network of four stations in the North Sea yielded information on the mean atmospheric structure in organized convective situations. During the second experiment phase in October 1981, cold air advection caused intense convective activity. Four periods of well‐organized open convection cells could be determined from NOAA satellite images. The present paper contains the results from the aerological data set, which allowed the derivation of mean profiles of the dynamic and thermodynamic quantities with acceptable accuracy, but also of the horizontal gradients of thermodynamic quantities. Finally, the evolution of the most pronounced cellular episode is presented in a case study. Cellular episodes appeared during rather cold and dry periods in which potential temperature, specific humidity, and equivalent potential temperature in the convection layer reached a relative minimum. However, none of the mean atmospheric profiles differ considerably from those found under convective conditions without cellular organization. During the cellular episodes, horizontal gradients show generally small values throughout the convection layer.
Aerosol size distributions and optical properties found in the marine boundary layer over the Atlantic Ocean
Authors: Hoppel W. A. , Fitzgerald J. W. , Frick G. M. , Larson R. E. , Mack E. J.
Published: February 2008

Measurements and analyses of the aerosol size distributions and optical properties found in the marine boundary layer (MBL) during the 1983 USNS Lynch cruise from Charleston, South Carolina, to Scotland via Canary Islands are presented. The data given are the most extensive and accurate measurements of the submicron marine aerosol size distribution to date and are supplemented by extensive meteorological observations. Eight detailed case studies of the evolution of the size distribution that occurred under different meteorological conditions are presented and discussed. The data indicate that repeated cycling of MBL air through nonprecipitating clouds at the top of the MBL is a major factor in shaping the size distribution and that new particle formation by heteromolecular, homogeneous nucleation is the most likely mechanism for sustaining the particle concentration below 0.04‐μm radius. Calculations of the scattering and extinction coefficients and optical depth of the MBL as a function of wavelength directly from the measured size distribution and MBL vertical structure are compared to measured values of the scattering coefficient and optical depth. These measured and calculated optical properties correlate well throughout the cruise and the results give a relatively consistent picture of the relationship between the aerosol size distribution and electromagnetic properties in the MBL.
Simulation of the three‐dimensional distribution of tracer during the Cross‐Appalachian Tracer Experiment
Authors: Shi Binqiang , Kahl Jon D. , Christidis Zaphiris D. , Samson Perry J.
Published: February 2008

This paper presents and applies a three‐dimensional Monte Carlo transport and dispersion model applicable to individual plumes traveling over regional (>200 km) scales. Transport is explicitly calculated using a mass‐consistent interpolated wind field. Dispersion is introduced solely by the interaction of vertical mixing and wind velocity shears. The degree of vertical mixing is parameterized contingent upon the Lagrangian time scale. The model was used to simulate the surface concentration of tracer released during the Cross‐Appalachian Tracer Experiments (CAPTEX). The results indicate that the scale of horizontal distribution of tracer observed during the CAPTEX may be explained by the influence of vertical wind velocity shear. The simulations also suggest that the surface “footprint” did not represent well the movement of the majority of mass of the plumes for CAPTEX releases 1 and 2. The majority of the mass was simulated to have traveled to the south of the surface footprint and stayed well above the surface. Thus it is inappropriate to specify fixed‐level trajectories as representative of the movement of pollutants over regional distances based on similarity of simulated to observed surface concentrations.
Permutation reactions of organic peroxy radicals in the troposphere
Authors: Madronich Sasha , Calvert Jack G.
Published: February 2008

Organic peroxy radicals are important intermediates in the atmospheric photooxidation of hydrocarbons. Laboratory studies indicate that these radicals react among themselves (permutation reactions) at rates which should compete with those for reaction with HO2 and NOx under some atmospheric conditions. Using the available laboratory data, we have developed a simplified method of representing the large number of atmospheric peroxy radical permutation reactions, and have included this in a detailed mechanism of hydrocarbon photooxidation. The potential importance of these reactions was studied for relatively low NOx conditions such as may be observed in the marine planetary boundary layer (PBL) and the Amazon PBL. The effects of the permutation reactions include suppression of organic peroxy radical concentrations, higher HO2 and H2O2 concentrations, shorter lifetimes for PAN and other peroxyacyl nitrates (with concomitant faster release of NOx), and production of substantial concentrations of alcohols and organic acids (including acetic acid). If the kinetic and mechanistic data used in the present study are at least roughly realistic, the peroxy radical reactions probably play an important role in the photochemistry of the clean troposphere.
International ultraviolet explorer observation of Venus SO2 and SO
Authors: Na Chan Y. , Esposito Larry W. , Skinner Thomas E.
Published: February 2008

Results of recent International Ultraviolet Explorer (IUE) observations of Venus made on January 20, 1987, and April 2 and 3, 1988, along with a reanalysis of the 1979 observations (Conway et al., 1979) are presented. The observations indicate that the amount of sulfur dioxide at the cloud tops of Venus declined by a factor of 8±4 from 380±70 ppb in 1979 to 50±20 ppb in 1987 and 1988. These values are consistent with the Pioneer Venus results (L. W. Esposito, A recalibration of the solar flux for Pioneer Venus results and a comparison of existing SO2 measurements on Venus, unpublished manuscript, 1989). We identify absorption features of sulfur monoxide for the first time, and estimate the SO mixing ratio above the cloud level is 20±10 ppb for 1979. This is consistent with photochemical models by Winick and Stewart (1980) and Yung and DeMore (1982) and with the upper limit from Wilson et al. (1981).
Measuring tropospheric HNO3: Problems and prospects for nylon filter and mist chamber techniques
Authors: Talbot R. W. , Vijgen A. S. , Harriss R. C.
Published: February 2008

We performed a series of laboratory and field measurements to evaluate the mist chamber technique for determining tropospheric HNO3 concentrations. Both the mist chamber and standard Nylon filter techniques exhibit high collection efficiency and excellent agreement measuring HNO3 vapors from a permeation source. When simultaneously sampling ambient air in eastern Virginia the Nylon filter measured an average of 70% higher HNO3 concentration than the mist chamber technique. Our results indicate that O3 causes a low‐level positive artifact interference in HNO3 measurements performed with the filter technique. This O3‐induced error is small, however, compared to the large difference between atmospheric HNO3 concentrations determined with the two techniques. We hypothesize that unidentified (organic?) nitrogen species in the atmosphere react for form NO3− on the filter and this phenomenon may interfere with Nylon filter measurements of HNO3 vapor. These potential interferences did not appear to affect measurements of HNO3 with the mist chamber method, but we are continuing studies to evaluate potential interference from various atmospheric species. Because the mist chamber technique employs an aerosol prefilter, it is probably best suited for measuring HNO3 concentrations when particle‐NO3− levels are low. In light of our preliminary results, we caution users of the Nylon filter method to continue to critically evaluate this technique for specificity in determining HNO3 vapor phase concentrations in the atmosphere, particularly at low concentrations typical of the remote troposphere.
Satellite measurements of large‐scale air pollution: Methods
Authors: Kaufman Yoram J. , Fraser Robert S. , Ferrare Richard A.
Published: February 2008

A method is presented for simultaneous determination of the aerosol optical thickness (τa), particle size (rm, geometric mean mass radius for a lognormal distribution) and the single scattering albedo (ω0, ratio between scattering and scattering +absorption) from satellite imagery. The method is based on satellite images of the surface (land and water) in the visible and near‐IR bands and is applied here to the first two channels of the Advanced Very High Resolution Radiometer (AVHRR) sensor. The aerosol characteristics are obtained from the difference in the upward radiances, detected by the satellite, between a clear and a hazy day. Therefore the method is mainly useful for remote sensing of large‐scale air pollution (e.g., smoke from a large fire or concentrated anthropogenic pollution), which introduces dense aerosol into the atmosphere (aerosol optical thickness ≥0.4) on top of an existing aerosol. The method is very sensitive to the stability of the surface reflectance between the clear day and the hazy day. It also requires accurate satellite calibration (preferably not more than 5% error) and stable calibration with good relative values between the two bands used in the analysis. With these requirements, the aerosol optical thickness can be derived with an error of Δτa = 0.08–0.15. For an assumed lognormal size distribution, the particle geometrical mean mass radius rm can be derived (if good calibration is available) with an error of Δrm = ±(0.10–0.20)μm, and ω0 with Δω0 = ±0.03 for ω0 close to 1 and Δω0 = ±(0.03–0.07) for ω0 about 0.8. Uncertainties in the type of the size distribution further increase the uncertainty in rm. The method was applied to AVHRR images of a forest fire smoke. The aerosol optical thickness and particle size derived from the AVHRR images are compared to the analysis of sun photometer measurements from the ground.
Remote sensing of biomass burning in the tropics
Authors: Kaufman Yoram J. , Tucker Compton J. , Fung Inez
Published: February 2008

A new method has been developed for the global assessment of trace gases and particulates emission from tropical biomass burning. The method is based on remote sensing of one emitted product: particulates. It uses daily meteorological satellite data with resolution of 1 km2. The visible (0.63 μm) and near‐infrared (0.84 μm) bands are used to determine the mass of particulates in the emitted smoke and to estimate the relative contribution of flaming and smoldering fires to the resulting smoke. The mid‐IR (3.5–3.9 μm) and the thermal infrared (10.5–11.4 μm) bands are used to detect and count fires in order to integrate the smoke result with the whole season and for the whole area of interest. The thermal channels are sensitive enough to detect flaming fires as small as 10 m×10 m and smoldering fires as small as 30 m×30 m. The detected mass of emitted particulates is converted into a mass of emitted trace gases using published relations between the emitted particulates and trace gases for the flaming and smoldering phases. The technique can be applied to regions where intensive biomass burning takes place. It is capable of monitoring the extent of current biomass burning, discovering new deforestation frontiers (unknown otherwise), and estimating quantitative contribution of biomass burning to changes in atmospheric composition. The method has been applied to a limited area where substantial deforestation has taken place. Analysis of the 1987 burning season shows that in Brazil (in a limited area between 6.5°–15.5°S and 55°–67°W) during the 3 months of the dry season (July 1 to September 30) there are up to 8000 fires a day (observed from space) each contributing 4500 t of CO2, 750 t of CO, and 26 t of CH4 to the atmosphere. During the dry season of 1987, it is estimated that 240,000 fires were burning in this area resulting in the emission of 1×1013 g of particulates, 7×1012 g of CH4, 2×1014 g of CO, and 1×1015 g of CO2. A comparison to estimates of global emissions is also given.
VHF radar observations of the dynamics of the summer polar mesopause region
Authors: Rüster Rüdiger , Reid Iain M.
Published: February 2008

Observations of the dynamics of the mesopause region over the Norwegian island of Andøya (69°N, 16°E) made during 2 days in summer 1987 using the mobile SOUSY VHF (53.5 MHz) Doppler Radar are reported. Measurements of the three mean wind components and the 12‐ and 24‐hour horizontal tidal components, as well as preliminary estimates of the component of the total upward flux of density‐normalized horizontal momentum in the SW–NE plane and the anisotropy of the horizontal wind are presented for the 83‐ to 90‐km height interval. Values of the component of the density‐normalized flux in the SW–NE plane for the 10‐min to 48‐hour period range, after the 12‐and‐24‐hour tidal components have been removed, vary from −1 m2 s−2 near 84 km to 16 m2 s−2 near 89 km. The major contribution is from the 10‐min to 12‐hour period range. The corresponding mean flow acceleration takes a mean value of −136 m s−1 d−1over the 83–90 km height interval. The anisotropy is considerable and may suggest the presence of standing waves.