bluuebunny/crossref_metadata_2025 huggingface dataset:
Ground‐based and airborne observations of carbon monoxide during NASA Measurements of Air Pollution From Satellite (MAPS) missions SRL‐1 and SRL‐2
Authors: Doddridge Bruce G. , Morales‐Morales Raymond , Rhoads Kevin P. , Merrill John T. , Novelli Paul C. , Dickerson Russell R. , Connors Vickie S. , Reichle Henry G.
Published: February 2004

Surface carbon monoxide (CO) data were acquired continuously at Heimaey, Iceland (63°24′N, 20° 18′W), Mace Head, Ireland (53° 19′N, 9°54′W), and Ragged Point, Barbados (13°15′N, 59°30′W), during April and October 1994, in support of Measurement of Air Pollution From Satellite (MAPS) Space Radar Laboratory (SRL) missions SRL‐1 and SRL‐2, respectively, measuring middle tropospheric CO from space. Observed median CO levels from the three surface sites during these two MAPS missions approximate the monthly median for 1994 and are mostly typical of data from prior years. For two of the sites, computed mission isentropic back‐trajectory ensemble probability fields are compared to seasonal (March‐May and September‐November) probability fields for 1994 and 1986–1995. Such comparisons help gauge the representativeness of (1) observed surface air quality at, and (2) isentropic flow to, these sites during the mission periods, in terms of intraseasonal and interannual variability. Results appear consistent with longer‐term flow climatological data and confirm the SRL‐1 and SRL‐2 mission periods are generally representative of the climatology applicable to these sites for the time of year. Lower free troposphere in situ CO data were acquired from an aircraft over the Maryland Eastern Shore on April 14 and October 3, 4, and 6. During the April flight a nearly linear gradient in CO with pressure from 1000–650 mbar of 225‐150 parts per billion by volume (ppbv) was observed. At 650 mbar, CO was quite steady around 150 ppbv; this value compares favorably with the MAPS CO data for the closest 5° ×; 5° grid box averaged April 13–15 of 105–120 ppbv. During SRL‐2 a three flight CO average of 125 ppbv observed at ∼725 mbar is in good agreement with the closest MAPS 5° × 5° grid box averaged October 3–7 of 90–105 ppbv. A layer of elevated CO at 845–740 mbar, most likely the result of synoptic‐scale transport, was observed during the October flights and seen to dissipate with time. The MAPS cloud‐filtered second‐by‐second CO data during concurrent shuttle overflights show temporal structure consistent with the in situ observations, indicating the MAPS weighting function may be capable of discerning features at lower altitudes than thought previously.
Biogenic sulfur emissions from the Gulf of Saint Lawrence and assessment of its impact on the Canadian east coast
Authors: Levasseur Maurice , Sharma Sangeeta , Cantin Guy , Michaud Sonia , Gosselin Michel , Barrie Leonard
Published: February 2004

We measured dimethylsulfide (DMS) concentrations over a grid of 79 stations covering the central part of the Gulf of Saint Lawrence and during a 24‐hour sampling period at a fixed station, in August 1993. Surface water DMS concentrations ranged from <0.9 to 9 nM over the sampling grid. DMS sea‐to‐air fluxes ranged from <0,1 to 23 μmol m−2 d−1, with a mean of 4.7 μmol m−2 d−1 for August. Atmospheric DMS levels measured during the cruise ranged from less than 0.5 nmol m−3 (12 parts per trillion by volume, or pptv) to 25 nmol m−3 (625 pptv) with a mean value of 11.9 nmol m−3 (291 pptv). Results from the 24‐hour sampling at the fixed station show that ventilation may represent the most important sink for surface DMS when wind speeds exceed approximately 8 m s−1. The relative magnitude of the biogenic and anthropogenic S components was estimated by comparing sulfur emissions from the gulf to the sulfur emissions from surrounding continental regions and to a sulfur budget calculated by using a Lagrangian box model. The first approach suggests that DMS emissions from the gulf represented at least 4% of total (biogenic plus anthropogenic) sulfur emissions from the Atlantic Provinces in August 1993. A Lagrangian forward motion trajectory shows that these biogenic emissions would affect all the Maritime Provinces and a portion of eastern Quebec. The second approach suggests that the contribution of the gulf to the total sulfur flux may reach 13% when compared with the anthropogenic inflow of sulfur from the Atlantic Provinces impacting the Maritimes. When the transboundary inflow of sulfur from the United States is also taken into account, the contribution of the gulf becomes 8%. Thus DMS emissions from coastal waters may represent a significant source of sulfur to the atmosphere.
Studying cumulative ozone exposures in Europe during a 7‐year period
Authors: Bastrup‐Birk Annemarie , Brandt Jørgen , Zlatev Zahari , Uria Ignacio
Published: February 2004

Ozone is one of the most harmful pollutants in the troposphere. High ozone concentrations can damage plants, animals and humans. The damaging effects depend on the magnitude of a critical level of a special parameter, the cumulative ozone exposure. This is why cumulative ozone exposures must be carefully studied. It is important to determine the relationships between relevant emissions (NOx emissions, human‐made VOC emissions, and/or a combination of NOx emissions and human‐made VOC emissions) and cumulative ozone exposures. All these issues are discussed in this paper. Meteorological data from seven consecutive years, from 1989 to 1995, have been used in the experiments with different scenarios for varying the emissions (the NOx emissions, the human‐made VOC emissions, as well as both the NOx emissions and the human‐made VOC emissions). The particular air pollution model used in this study is the Danish Eulerian Model. Several hundred runs with different input data (meteorological data and/or emission data) have been performed. Advanced visualization techniques are used to interpret the large amount of digital data collected in these runs and to show clearly different trends and relationships that are normally hidden behind millions and millions of numbers. The model results were compared with measurements taken at more than 80 stations located in different European countries. The experiments indicate that it is sufficient to carry out computations over 5 consecutive years in order to eliminate the influence of extreme meteorological conditions (very warm or very cold summer months) on the cumulative ozone exposures, while this effect is clearly seen if less than 5 years are used in the experiments. It is shown that the relationship between the emissions (NOx and/or human‐made VOC emissions) and the cumulative ozone exposures is in general nonlinear. Finally, it is illustrated that the critical values for ozone exposures are exceeded in most of Europe (in many areas by more than 7 times).
Gas‐to‐particle conversion of tropospheric sulfur as estimated from observations in the western North Pacific during PEM‐West B
Authors: Andronache C. , Chameides W. L. , Davis D. D. , Anderson B. E. , Pueschel R. F. , Bandy A. R. , Thornton D. C. , Talbot R. W. , Kasibhatla P. , Kiang C. S.
Published: February 2004

Aircraft observations during the Pacific Exploratory Mission in the western Pacific Ocean, phase B (PEM‐West B), taken in February–March 1994, have been used to constrain a numerical model that calculates local concentrations of gaseous H2SO4 rates of homogeneous nucleation, and concentrations of newly formed, nanometer‐sized particles. The data was selected from 13 flights over the western Pacific Ocean that covered an altitude range from the boundary layer (BL) to the upper troposphere (UT) and latitudes from 10°S to 60°N. The largest nucleation rates were calculated for the data from the flights over the temperate latitudes (λ>30°N). Within these latitudes, homogeneous nucleation rates averaged about 1–100 particles cm−3 s−1. Significantly smaller nucleation rates were calculated for the tropical (λ<20°N) and subtropical (20°N<λ<30°N) regions. In the tropics, average nucleation rates in excess of 10 particles cm−3 s−1 were limited to the UT. In the subtropics, large average nucleation rates in excess of 1 particle cm−3 s−1 were obtained in the BL and in the UT, and average rates of about 10−1 particles cm−3 s−1 were obtained for the rest of the troposphere. The relatively large nucleation rates calculated for the temperate latitudes could be largely attributed to the cold temperatures encountered in this region during the PEM‐West B flights. For the data from the tropical and subtropical flights, little or no homogeneous nucleation was calculated for the average conditions encountered in the BL and midtroposphere (MT). Instead, significant nucleation was limited either to the UT or to several small‐scale events. These enhanced nucleation events were generally characterized by spikes in relative humidity and low aerosol surface density. However, the strongest nucleation events, with homogeneous nucleation rates of about 10 particles cm−3 s−1, were associated with high concentrations of SO2, most likely as a result of pollution from the Asian continent. Our results imply that in regions in which homogeneous nucleation is dominated by small‐scale fluctuations, approaches that attempt to infer nucleation rates using average or typical conditions will grossly underestimate the actual average rate of nucleation.
Earth surface reflectivity climatology at 340–380 nm from TOMS data
Authors: Herman J. R. , Celarier E. A.
Published: February 2004

The 340–380 nm (UV) Lambertian equivalent reflectivities (LER) of the Earth's surface, between the latitudes ±70°, are constructed from 14.5 years of radiances measured by Nimbus‐7/total ozone mapping spectrometer (November 1978 to May 1993). The surface LER values are obtained from the minimum reflectivity values for each 1°×1.25° (latitude × longitude) pixel with statistically improbable outlier values removed. The resulting LER climatology shows low surface reflectivity values over the entire globe at 340 and 380 nm that are nearly independent of wavelength (the difference is less than 0.2%). In general, the LER is lower over the land (2–4%) than over the oceans (5–8%), though both land and water have features outside of these ranges. Monthly maps of LER are derived that include seasonally persistent cloud features, as well as showing seasonal surface variations. There are low reflectivity regions in the ocean coastal waters that appear to be indicative of chlorophyll or silt from wave action or from rivers. There also are mid‐ocean areas of comparatively high reflectivity with a seasonal variation that is not solar zenith angle dependent. These areas of high ocean reflectivity correlate with coastal zone color scanner observations that were associated with the absence of phytoplankton (clear water).
Measurements of CO and O3 at Shemya, Alaska
Authors: Jaffe Dan , Yurganov Leonid , Pullman Eric , Reuter Joseph , Mahura Alexander , Novelli Paul
Published: February 2004

In situ measurements of surface CO were conducted from June 1994 to May 1995, and surface ozone was measured from February to May, 1995, at Shemya, Alaska (52o44'N, 174o06'E) using nondispersive infrared‐gas filter correlation (GFC) and UV absorption spectroscopy, respectively. Over the same period, air samples were collected in flasks for analysis of CO and other trace gases as part of the NOAA‐CMDL cooperative air sampling network. We compared the continuous GFC measurements with the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory (NOAA‐CMDL) flask data. Over this 1‐year period, CO mixing ratios varied between 60 and 250 parts per billion by volume (ppbv). Within this range, the comparison between the two measurements is quite good, with an overall R2 of 0.953 and an average difference of 3.1%. A seasonal cycle is apparent in the CO data, with a springtime maximum and a summer minimum. Synoptic influences on the data include transport from the lower‐latitude Pacific, bringing air with very low CO mixing ratios to Shemya, and, occasionally, transport from industrial areas in east Asia, including northern China, Japan, and eastern Russia. A scatterplot of CO versus O3 using all the data shows essentially no relationship at this remote site. This result implies that the primary sources and sinks for these trace gases are different at this location. However, during a few 12‐ to 48‐hour periods in fall and late spring, enhancements in CO or in both CO and O3 were observed. During these periods, isentropic back trajectories indicate transport from the west and southwest. However, the trajectories are often difficult to interpret due to looping and are of short duration due to impact at the surface. These complexities are associated with the presence of cyclonic systems in the region. The local meteorological data suggest that the enhanced concentrations occurred around the time when these cyclonic systems passed near the sampling site. Synoptic surface pressure maps indicate that these cyclonic systems formed or crossed industrial regions in east Asia and passed near Shemya on their way to the Bering Sea. This process suggests a role for transport of anthropogenic pollutants by cyclonic systems moving northward along the western edge of the Pacific Ocean.
Reactive nitrogen and its correlation with O3 and CO over the Pacific in winter and early spring
Authors: Koike M. , Kondo Y. , Kawakami S. , Nakajima H. , Gregory G. L. , Sachse G. W. , Singh H. B. , Browell E. V. , Merrill J. T. , Newell R. E.
Published: February 2004

Measurements of NO, NOy, O3, and CO were made during NASA's Global Tropospheric Experiment/Pacific Exploratory Mission‐West B (GTE/PEM‐West B) carried out over the western Pacific in February and March 1994. NOx was calculated from NO using a photostationary state model ((NOx)mc). Correlations between these species are presented, and some insights into the sources of NOx and NOy are described. The boundaries between the lower, middle, and upper troposphere have been defined at potential temperatures of 311 K and 328 K, which correspond to the geometric altitudes of about 5 and 9 km at 30°N. Enhancements in the mixing ratios of NOy and CO were observed in the lower and middle troposphere. A positive correlation was found between these two species suggesting that the high NOy values were due to anthropogenic emissions over the continental surface. On the other hand, O3 increased little with increase in CO. As a result, NOy/O3 ratios were higher in air more influenced by pollution. NOy values in 55 and 28% of the air masses sampled in the lower and middle troposphere, respectively, were higher than the clean free tropospheric NOy‐O3 range when O3 values simultaneously observed were used. High (NOx)mc/NOy ratios between 0.15 and 0.3 were found in the boundary layer with relatively low mixing ratios of CO and NOy during the three flights. These air masses were transported from a higher altitude (∼5 km) and a higher latitude (∼50°N) within a few days. The peroxyacetyl nitrate (PAN)/NOy ratios were generally high (∼0.4) in these air masses, and the thermal decomposition of PAN was a probable source of NOx. In the middle troposphere the (NOx)mc mixing ratio did not generally increase with NOy or CO, suggesting that the transport of air masses affected by anthropogenic emissions did not increase the NOx level significantly. In the upper troposphere, very minor effects from the continental surface sources were seen in the CO mixing ratio. By contrast, NOy values in 33% of the air masses were higher than those expected when stratospheric air intrusion is assumed to be a single source of NOy based on NOy‐O3 correlation analyses. This result suggests significant free tropospheric NOy sources, namely exhaust from the aircraft and NO production by lightning activity. In fact, spikes in the (NOx)mc mixing ratios were observed near the aircraft corridor south of Tokyo at an altitude of 10 km. These two free tropospheric NOx sources were considered to be important in determining the levels of the upper tropospheric NOx and NOy during PEM‐West B.
Research education
Authors: Hansen James , Harris Carolyn , Borenstein Samuel , Curran Brendan , Fox Mitchell
Published: February 2004

Introduction

How can we get the public to appreciate the way scientific understanding advances via iterative research? How can we provide females and underrepresented minorities an opportunity to be involved in science early enough in their schooling to make a difference in career motivation? How can research laboratories help improve science education in our schools and prepare students with skills that they will need in the workforce? We do not have the answers to these questions. Indeed, we are only beginning to work together, as researchers and educators, on these topics. However, the Editor, upon seeing the large number of student and educator coauthors on our paper in this issue of Journal of Geophysical Research, invited us to describe our fledgling program, with the hope of stimulating dialogue on a topic of increasing interest.
A brief climatology of eddy diffusivities over White Sands Missile Range, New Mexico
Authors: Nastrom G. D. , Eaton F. D.
Published: February 2004

Observations of the Doppler spectral width made using the VHF profiler radar at White Sands Missile Range, New Mexico, are used to estimate the eddy diffusion coefficient Kz at 5–20 km on an hourly basis. The data used span the period 1991–1995. Medians of the hourly values of Kz range from ∼3 m2/s near 5km to about 0.3 m2/s near 14km. The logarithms of the individual hourly values are approximately normally distributed. Seasonal median values of log Kz are nearly the same at all heights during autumn through spring, while the summer values are about twice as large as the values for other seasons. Hourly values of log Kz are negatively correlated with the static stability, are positively correlated with the vertical shear of the horizontal wind, and show weak negative correlation with the Richardson number during all seasons. The correlation of log Kz with the horizontal wind speed is positive in the winter, indicating that the magnitude of Kz is determined by synoptic weather systems then, and negative in the summer, indicating that convective processes are most important in determining Kz in the summer. The autocorrelation of log Kz as a function of vertical separation decreases more slowly with increasing vertical separation in the troposphere than in the stratosphere. The median values of log Kz that we find compare very well with those of past studies near the tropopause level and above, but in the troposphere they are significantly larger than those reported from the middle and upper atmosphere radar in Japan; this difference is discussed in terms of differences in the local terrain and the climate of the troposphere.
An inlet/sampling duct for airborne OH and sulfuric acid measurements
Authors: Eisele F. L. , Mauldin R. L. , Tanner D. J. , Fox J. R. , Mouch T. , Scully T.
Published: February 2004

An inlet assembly has been designed, tested, and used for the airborne measurements of OH and sulfuric acid. The inlet sampling duct, which incorporates a shroud connected to two nested, restricted flow ducts, slows air velocity by approximately a factor of 16 while maintaining a uniform and well‐defined flow. Qualitative wind tunnel tests showed that an inlet shroud that incorporates a 3:1 inner surface and 4.5:1 outer elliptical front surface can straighten the airflow at angles of attack of up to 18°–20° with no visible signs of turbulence. Tests using a Pitot tube to scan the flow velocity profile of the restricted flow ducts showed that the shroud, coupled to inlet ducts, could slow the flow and provide a relatively flat average velocity profile across the central portion of the ducts at angles of attack up to 17°. Tests performed using a chemical tracer showed that at angles of attack where the Pitot tube measurements began to indicate slight flow instabilities (17°–24°), there was no mixing from the walls into the center of the inlet. The inlet assembly also possesses the ability to produce a fairly uniform concentration of OH in the relatively constant velocity portion of the inner duct for instrument calibration. Actual measurements of rapidly changing OH and H2SO4 provide both additional evidence of proper inlet operation and new insight into H2SO4 production and loss in and around clouds.
A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southern hemispheres
Authors: Carpenter Lucy J. , Monks Paul S. , Bandy Brian J. , Penkett Stuart A. , Galbally Ian E. , Meyer C. P. (Mick)
Published: February 2004

Peroxy radicals and other important species relevant to ozone photochemistry, including ozone, its photolysis rate coefficient jO(1D), NOx (NO + NO2), and peroxides, were measured at the coastal sites of Cape Grim, Tasmania, in January/February 1995 during the Southern Ocean Atmospheric Photochemistry Experiment (SOAPEX 1) and Mace Head, Western Ireland, in May 1995 during the Atlantic Atmospheric Photochemistry Experiment (ATAPEX 1). At both sites it was observed that the relationship between peroxy radical (HO2 + RO2) concentrations and jO(1D) switched from a square root dependence in clean oceanic or “baseline” air to a first‐order dependence in more polluted air. Simple algorithms derived from a photochemical reaction scheme indicate that this switch‐over occurs when atmospheric NO levels are sufficient for peroxy radical reaction with NO to compete with radical recombination reactions. At this crucial point, net tropospheric ozone production is expected to occur and was observed in the ozone diurnal cycles when the peroxy radical/jO(1D) dependencies became first order. The peroxy radical/jO(1D) relationships imply that ozone production exceeds destruction at NO levels of 55±30 parts per trillion by volume (pptv) at Mace Head during late spring and 23±20 pptv at Cape Grim during summer, suggesting that the tropospheric ozone production potential of the southern hemisphere is more responsive to the availability of NO than that of the northern hemisphere.
Cloud factor and seasonality of the indirect effect of anthropogenic sulfate aerosols
Authors: Kogan Z. N. , Kogan Y. L. , Lilly D. K.
Published: February 2004

A method for evaluation of the indirect shortwave effect of anthropogenic sulfate aerosols based on the empirically derived cloud climatology is described and applied. The method is simple and computationally efficient which allows many sensitivity tests to be conducted. The tests presented focus mainly on the effects of cloud amounts and types as well as on seasonality of the indirect forcing. We found the indirect shortwave forcing estimated from cloud climatology (−1.1 W m−2, with a hemispheric difference of 0.4 W m−2) is close to that obtained from general circulation model simulations in previous studies. The hemispheric forcing has a strong seasonal cycle with the northern hemisphere (NH) forcing exceeding that of the southern hemisphere (SH) during the NH spring and summer, and the SH forcing prevailing during the SH spring and summer. We also estimate that single‐layer St/Sc contribute most to the aerosol indirect forcing (60%) with an additional 25% from St/Sc overlapped with Ci/Cs/Cc and 15% from St/Sc overlapped with As/Ac. The upper and middle level clouds overlapping the low level stratiform cloud layers reduce the indirect forcing by more than a factor of 2 (from −2.5 to −1.1 W m−2). The estimate of the indirect forcing of −1.1 W m−2 is based on climatological mean values of transmittance for Ac/As and Ci/Cs/Cc. The transmittance of these clouds, however, may vary in a wide range resulting in a large regional and seasonal variability of the aerosol indirect forcing.
Measurements of nitrogen oxides and a simple model of NOy fate in the remote North Atlantic marine atmosphere
Authors: Peterson Matthew C. , Honrath Richard E. , Parrish David D. , Oltmans Samuel J.
Published: February 2004

NO and NOy (total reactive oxidized nitrogen) were measured at a site in the Azores (27.322°W, 38.732°N, 1 km altitude) over a 3 week period in August and September 1993, during the first summer intensive of the North Atlantic Regional Experiment (NARE). These measurements were performed to determine background reactive nitrogen oxides levels and to assess the impact that long‐range transport of reactive nitrogen oxides associated with human activities have on these levels. Median NOy mixing ratios during background marine boundary layer (MBL) periods ranged from 59 to 93 parts per trillion by volume (pptv), with an overall median of 73 pptv. Analysis of back trajectories, low and uncorrelated CO and O3 levels, and low levels of MBL NOy indicate that the central North Atlantic region was not influenced by direct transport of anthropogenic emissions during the period of this study. Changes in NOy levels during two MBL periods with adjacent in and out‐of‐cloud events indicated that up to 45–47% of MBL NOy was scavenged by clouds. However, mean NOy levels during all in‐cloud periods (∼70 pptv) and all out‐of‐cloud periods (∼80 pptv) were not significantly different, apparently because of variability in MBL NOy levels. In addition to the MBL periods, there were two periods when the site was within the free troposphere (FT), as indicated by vertical soundings and weather conditions at the site. FT NOy mixing ratios were ≥280 pptv and ≥400 pptv during these two periods. The median clear‐sky FT NO level during the hour centered on solar noon was 16 pptv. A mass balance model considering FT/MBL exchange and MBL removal processes is used to find the NOy MBL effective first‐order loss lifetime (∼1.2 days) and the NOy, MBL e‐folding response time due to both effective first‐order loss processes and subsidence‐induced ventilation of the MBL (∼0.9 days). The apparent rapid loss of MBL NOy, implies that it will respond rapidly to changes in the overlying FT, but that correlations of NOy with trace gases with slower MBL removal, such as O3 and CO, will be degraded within the subsidence‐influenced MBL.
Comparison of cloud frequency data from the high‐resolution infrared radiometer sounder and the Stratospheric Aerosol and Gas Experiment II
Authors: Wylie Donald P. , Wang Pi‐Huan
Published: February 2004

Climatologies of cloud frequencies were compared from two satellite sensors, the high‐resolution infrared radiometer sounder (HIRS) and the Stratospheric Aerosol and Gas Experiment II (SAGE II), during two summers (June, July, and August 1989 and 1990) and two winters (December, January, and February 1989–1990 and 1990–1991). Both sensors were operating simultaneously during these periods, which spanned 12 months. The two data sets generally agreed on the locations of clouds; however, SAGE II reported higher frequencies of clouds by 12–22 percentage points. The differences in the frequencies of clouds appear to be caused by differences in sensor sensitivity and scanning field of view sizes, both of which would have the same effect. SAGE II has a higher sensitivity to thinner clouds and a larger field of view than the HIRS. The vertical distributions of clouds also show close agreement except for the low levels (below 3 km) and the upper troposphere where SAGE II reported more clouds. The very thin subvisual cirrus detected only by SAGE II also were generally found in the same locations where HIRS reported denser clouds, indicating a relationship between subvisual cirrus and other cloud forms.
Methyl cyanide and hydrogen cyanide measurements in the lower stratosphere: Implications for methyl cyanide sources and sinks
Authors: Schneider J. , Bürger V. , Arnold F.
Published: February 2004

Concentrations of CH3CN and HCN have been measured in the lower stratosphere by aircraft‐based ion‐molecule reaction mass spectrometry. The mean HCN volume mixing ratio of 164 parts per trillion by volume (pptv) is consistent with previous infrared remote sensing data (160 pptv). The measured CH3CN volume mixing ratios markedly exceed most previous lower stratospheric values and reveal a significant decrease from 160 to 110 pptv between 1.0 and 4.2 km above the tropopause. This latter feature suggests a stratospheric CH3CN lifetime much shorter than thought previously, which can be explained by an additional stratospheric sink, maybe ioncatalyzed conversion of CH3CN to HCN. Our present data indicate a mean global tropospheric CH3CN source of 1.6×1012 g CH3CN per year which is slightly larger than the CH3CN source inferred from most previous atmospheric measurements of CH3CN but is in agreement with estimations inferred from laboratory simulation experiments of biomass burning.
Analysis and validation of GPS/MET data in the neutral atmosphere
Authors: Rocken C. , Anthes R. , Exner M. , Hunt D. , Sokolovskiy S. , Ware R. , Gorbunov M. , Schreiner W. , Feng D. , Herman B. , Kuo Y.‐H. , Zou X.
Published: February 2004

The Global Positioning System/Meteorology ( GPS/MET) Program was established in 1993 by the University Corporation for Atmospheric Research ( UCAR) to demonstrate active limb sounding of the Earth's atmosphere using the radio occultation technique. The demonstration system observes occulted GPS satellite signals received by a low Earth orbiting ( LEO) satellite, MicroLab‐1, launched April 3,1995. The system can profile ionospheric electron density and neutral atmospheric properties. Neutral atmospheric refractivity, density, pressure, and temperature are derived at altitudes where the amount of water vapor is low. At lower altitudes, vertical profiles of density, pressure, and water vapor pressure can be derived from the GPS/MET refractivity profiles if temperature data from an independent source are available. This paper describes the GPS/MET data analysis procedures and validates GPS/MET data with statistics and illustrative case studies. We compare more than 1200 GPS/MET neutral atmosphere soundings to correlative data from operational global weather analyses, radiosondes, and the GOES, TOVS, UARS/MLS and HALOE orbiting atmospheric sensors. Even though many GPS/MET soundings currently fail to penetrate the lowest 5 km of the troposphere in the presence of significant water vapor, our results demonstrate 1°C mean temperature agreement with the best correlative data sets between 1 and 40 km. This and the fact that GPS/MET observations are all‐weather and self‐calibrating suggests that radio occultation technology has the potential to make a strong contribution to a global observing system supporting weather prediction and weather and climate research.
Determining marine aerosol scattering characteristics at ambient humidity from size‐resolved chemical composition
Authors: Howell Steven G. , Huebert Barry J.
Published: February 2004

Although the variation of aerosol optical properties with humidity depends critically on particle size and chemical composition, existing models usually employ empirical growth factors for water uptake. For some size ranges and many types of particles these empirical factors are not well known. We describe here a model that applies a thermodynamic analysis to arbitrary aerosol chemical size distributions to compute water uptake, refractive index, number distribution, and optical extinction. By starting with the fundamental chemistry of the aerosols the model is able to compute the derivative of extinction with sulfate, sulfate plus ammonium, and other scenarios that may be derived from global change and pollution control strategies. It can also supply information on the variation of aerosol size and extinction with humidity and with details of the aerosol size distribution. We demonstrate this model using five detailed chemical size distributions measured with a cascade impactor in the marine boundary layer. The results are in good agreement with published extinction coefficients and with nephelometer data collected in concert with one of our samples. Calculated non‐sea‐salt sulfate mass‐scattering efficiencies of our samples ranged from 0.6 to 2.6 g m−2 for dry particles and 5.3 to 13 g m−2 at 80% relative humidity.
Measurements of the downward longwave radiation spectrum over the Antarctic Plateau and comparisons with a line‐by‐line radiative transfer model for clear skies
Authors: Walden Von P. , Warren Stephen G. , Murcray Frank J.
Published: February 2004

A 1‐year field program was conducted at South Pole Station in 1992 to measure the downward infrared radiance spectrum at a resolution of 1 cm−1 over the spectral range 550–1667 cm−1. The atmosphere over the Antarctic Plateau is the coldest and driest on Earth, where in winter, surface temperatures average about −60°C, the total column water vapor is as low as 300 μm of precipitable water, and the clear‐sky downward longwave flux is usually less than 80 W m−2. Three clear‐sky test cases are selected, one each for summer, winter, and spring, for which high‐quality radiance data are available as well as ancillary data to construct model atmospheres from radiosondes, ozonesondes, and other measurements. The model atmospheres are used in conjunction with the line‐by‐line radiative transfer model (LBLRTM) to compare model calculations with the spectral radiance measurements. The high‐resolution calculations of LBLRTM (≈0.001 cm−1) are matched to the lower‐resolution measurements (1 cm−1) by adjusting their spectral resolution and by applying a correction for the finite field of view of the interferometer. In summer the uncertainties in temperature and water vapor profiles dominate the radiance error in the LBLRTM calculations. In winter the uncertainty in viewing zenith angle becomes important as well as the choice of atmospheric levels in the strong near‐surface temperature inversion. The spectral radiance calculated for each of the three test cases generally agrees with that measured, to within twice the total estimated radiance error, thus validating LBLRTM to this level of accuracy for Antarctic conditions. However, the discrepancy exceeds twice the estimated error in the gaps between spectral lines in the region 1250–1500 cm−1, where emission is dominated by the foreign‐broadened water vapor continuum.
Evidence of heterogeneous chemistry on sulfate aerosols in stratospherically influenced air masses sampled during PEM‐West B
Authors: Kotamarthi V. R. , Rodriguez J. M. , Sze N. D. , Kondo Y. , Pueschel R. , Ferry G. , Bradshaw J. , Sandholm S. , Gregory G. , Davis D. , Liu S.
Published: February 2004

Signatures of the N2O5 hydrolysis by sulfate aerosols have been previously documented, primarily from balloon and remote‐sensing platforms, by measurements of nitrogen species aboard the NASA ER‐2 flying at an altitude of approximately 20 km and some ER‐2 and DC‐8 measurements near the tropopause during stratospheric campaigns. This study documents such signatures in the NOx/NOy ratios derived from DC‐8 measurements during Pacific Exploratory Measurements in the Western Pacific Ocean (PEM‐West B) in stratospherically influenced air masses sampled during a level leg at an altitude of 10.7 km in flight 17 out of Japan. Despite the very low abundance of total bromine, we also show that heterogeneous hydrolysis of BrNO3 on sulphate aerosols can catalytically convert NOx and liquid H2O into HNO3 and OH and thereby lower the calculated equilibrium NOx/NOy by about 20 to 35% in these air masses, bringing closer agreement with the nitrogen partitioning deduced from measurements. However, the NOx/NOy ratios calculated from a model including heterogeneous chemistry were a factor of 3 smaller than ratios derived from data for a segment of this flight leg when DC‐8 measurements indicated a stronger tropospheric influence. We also modeled the equilibrium partitioning of nitrogen species for all upper tropospheric air masses encountered by the DC‐8; since NOy in the troposphere may contain nonnegligible contributions from long‐lived nitrates (such as peroxyacetylnitrate), we have compared instead modeled and measured NOx/HNO3. The calculated equilibrium NOx/HNO3 ratios using only gas‐phase chemistry are on the average smaller than those deduced from measurements in upper tropospheric air masses; inclusion of N2O5 hydrolysis reduces these ratios by an additional 20%, thus worsening the discrepancy. These results suggest a rapid transition from “denoxified” conditions in the lower stratosphere to “renoxified” conditions in the upper troposphere. This transition could be due to intrinsically different chemistry in the troposphere. Alternatively, rapid transport in the troposphere could keep the NOx and HNO3 away from chemical equilibrium. Detailed analysis of current and future tropospheric data could shed light on this issue.
Low‐ozone pockets explained
Authors: Morris Gary A. , Kawa S. R. , Douglass A. R. , Schoeberl M. R. , Froidevaux L. , Waters J.
Published: February 2004

Pockets of low ozone have been observed on numerous occasions in anticyclones at middle to high latitudes in the middle stratosphere. Air masses within the anticyclones at altitudes near 850 K (∼32 km) contain ∼25% less ozone than the surrounding air. Trajectory calculations have revealed that much of the air within the pockets originates in the tropics or subtropics at higher altitudes several weeks earlier. Previous studies have, however, left unanswered a number of questions related to the formation of the low‐ozone regions. Using a Lagrangian chemical model with initialization based upon observations from the Upper Atmosphere Research Satellite (UARS), we examine in detail an event in March 1993. Our results demonstrate that the development of the observed ozone pockets can be explained with our current understanding of chemistry and dynamics. The primary mechanism responsible for the development of these low‐ozone regions is the isolation of air at high latitudes for periods of time long enough that significant ozone loss toward the local photochemical equilibrium can occur. Such behavior is different from that of the surrounding air masses that move from middle to high latitudes and back again over the course of a few days. The dynamical behavior associated with these latter air masses results in ozone concentrations more consistent with lower‐latitude equilibrium values.
Corona emission thresholds for three types of hydrometeor interaction in thunderclouds
Authors: Blyth A. M. , Christian H. J. , Latham J.
Published: February 2004

Laboratory studies have been conducted of the conditions under which glancing collisions, at relative velocities V characteristic of those occurring in thunderstorms, of three types of hydrometeor pairs of precipitation dimension (such as (1) warm drop pairs, (2) supercooled drop pairs, and (3) a supercooled drop and a graupel pellet) produce a corona discharge in an electric field E. In each case, the observed corona is emitted at the tip of an ephemeral liquid filament, of length greater than the dimensions of the interacting hydrometeors, drawn out during each interaction. For each type of hydrometeor pair, the probability f that corona was produced during an interaction increased steadily from zero for increasing values of E above about 150 kV/m, and was significantly in excess of 50% for values of E = 400 kV/m, which is probably about the maximum ambient value occurring in a thunderstorm. We conclude that if the associated hydrometeors are present in strongly electrified regions of thunderstorms (unlikely for interaction type 1 but manifestly possible for types 2 and 3, corona initiation leading to the production of lightning could result from each of the three types of interaction studied.
An assessment of ozone photochemistry in the extratropical western North Pacific: Impact of continental outflow during the late winter/early spring
Authors: Crawford J. , Davis D. , Chen G. , Bradshaw J. , Sandholm S. , Kondo Y. , Liu S. , Browell E. , Gregory G. , Anderson B. , Sachse G. , Collins J. , Barrick J. , Blake D. , Talbot R. , Singh H.
Published: February 2004

This study examines the influence of photochemical processes on tropospheric ozone distributions over the extratropical western North Pacific. The analysis presented here is based on data collected during the Pacific Exploratory Mission‐West Phase B (PEM‐West B) field study conducted in February‐March 1994. Sampling in the study region involved altitudes of 0–12 km and latitudes of 10°S to 50°N. The extratropical component of the data set (i.e., 20–50°N) was defined by markedly different photochemical environments north and south of 30°N. This separation was clearly defined by an abrupt decrease in the tropopause height near 30°N and a concomitant increase in total O3 column density. This shift in overhead O3 led to highly reduced rates of O3 formation and destruction for the 30–50°N latitude regime. Both latitude ranges, however, still exhibited net O3 production at all altitudes. Of special significance was the finding that net O3 production prevailed even at boundary layer and lower free tropospheric altitudes (e.g., ≤ 4 km), a condition uncommon to Pacific marine environments. These results reflect the strong impact of continental outflow of O3 precursors (e.g., NO and NMHCs) into the northwestern Pacific Basin. Comparisons with PEM‐West A, which sampled the same region in a different season (September‐October), revealed major differences at altitudes below 4 km, the altitude range most influenced by continental outflow. The resulting net rate of increase in the tropospheric O3 column for PEM‐West B was 1–3% per day, while for PEM‐West A it was approximately zero. Unique to the PEM‐West B study is the finding that even under wintertime conditions substantial column production of tropospheric O3 can occur at subtropical and mid‐latitudes. While such impacts may not be totally unexpected at near coast locations, the present study suggests that the impact from continental outflow on the marine BL could extend out to distances of more than 2000 km from the Asian Pacific Rim.
Reconstructing recent atmospheric trace gas concentrations from polar firn and bubbly ice data by inverse methods
Authors: Rommelaere Vincent , Arnaud Laurent , Barnola Jean‐Marc
Published: February 2004

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.
Validation of an off‐line three‐dimensional chemical transport model using observed radon profiles: 1. Observations
Authors: Kritz Mark A. , Rosner Stefan W. , Stockwell D. Zoe
Published: February 2004

We present in Table 1 of this paper a series of free tropospheric radon profiles, obtained in the summer of 1994 on flights originating from Moffett Field, California (37.4°N, 122.0°W). These data were collected with the intent of acquiring a high‐quality, statistically significant set of observations, in one season and at one location, suitable for use in the development and validation of three‐dimensional global circulation and chemical transport models, as demonstrated in the companion paper [Stockwell, et al., this issue]. The profiles, which extend from the surface to 11.5 kilometers, were obtained on 11 flights flown in the period June 3 to August 16. A series of high‐pressure whole‐air samples (typically 11 or 12 per profile) were collected as the plane ascended to altitude, and analyzed immediately after each flight in a ground‐based laboratory. A thorough discussion of sampling, analysis, calibration, and quality control procedures is provided.
Calculation of electrical conductivity from ion‐aerosol balance equations
Authors: Dhanorkar Savita , Kamra A. K.
Published: February 2004

The ion‐aerosol balance equations are solved to study the effect of aerosol concentration on electrical conductivity for different ionization rates taking bimodal lognormal size distribution for the grand average continental aerosol particles and using size dependent attachment and coagulation coefficients for the aerosol particles. The results show that the inverse relationship between the polar conductivity and aerosol concentration exists only up to a certain critical value of aerosol concentration which depends upon the prevailing ionization rate. Further increase in aerosol concentration causes an increase in polar conductivity due to the contribution made to it by large ions. However, this increase in conductivity is again restricted by recombination of charged aerosols in a highly polluted atmosphere. Further, it is shown that in polluted urban environments where particulate concentration is large and variable the charge equilibrium is attained faster when the effect of recombination of charged aerosols is included.
Application of the dispersion formula to long‐and short‐period gravity waves: Comparisons with ALOHA‐93 data and an analytical model
Authors: Munasinghe G. , Hur H. , Huang T. Y. , Bhattachryya A. , Tuan T. F.
Published: February 2004

During the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA) Campaign on October 10, 1993, a wave structure with a sharp front covering significant parts of the sky was observed to move with a phase velocity of 76 m/s at a period of 4 to 5 min. Simultaneous observations of the Green line and the OH emission brightness showed a 180° phase diffeence. We have two objectives. (1) By using a dispersion formula, we first separated the true partial wave guidance for long‐period waves from the background effects and showed explicitly that many partial modes previously thought to exist do not in fact exist. In this way, we can show that two very different methods for computing partial modes which previously gave very different results can now be reconciled. We showed that by lowering the period the modes became, first, virtually guided and then fully guided. (2) We then showed that the long‐period S2 partial mode eventually became a two‐node fully guided mode, which at periods in the range of 4.6 min, had not only phase velocities comparable to the observed result, but also a phase reversal (from the two‐node structure) at altitudes in the vicinity of the two airglow emission peaks. At those periods, the dispersion curves were shown to be out of the range of the nearest “kissing” mode and were thus largely unaffected by interference from the stratospheric duct. The results agree well with an analytic model. The wave explanation may in some way complement the other explanations (such as the bore, or soliton) for the same event mentioned in presentations elsewhere.