T. L. Thompson

Airborne gas chromatograph for in situ measurements of long-lived species in the upper troposphere and lower stratosphere

A new instrument, the Airborne Chromatograph for Atmospheric Trace Species IV (ACATS-IV), for measuring long-lived species in the upper troposphere and lower stratosphere is described. Using an advanced approach to gas chromatography and electron capture detection, the instrument can detect low levels of CFC-11 (CCl 3 F), CFC-12 (CCl 2 F 2 ), CFC-113 (CCl 2 F-CClF 2 ), methyl chloroform (CH 3 CCl 3 ), carbon tetrachloride (CCl 4 ), nitrous oxide N 2 O), sulfur hexafluoride (SF 6 ), Halon-1211 (CBrClF 2 ), hydrogen (H 2 ), and methane (CH 4 ) acquired in ambient samples every 180 or 360 s. The instrument operates fully-automated onboard the NASA ER-2 high-altitude aircraft on flights lasting up to 8 hours or more in duration. Recent measurements include 24 successful flights covering a broad latitude range (70°S-61°N) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/ MAESA) campaign in 1994.

A Novel Method for Estimating Light-Scattering Properties of Soot Aerosols Using a Modified Single-Particle Soot Photometer

A Single-Particle Soot Photometer (SP2) detects black refractory or elemental carbon (EC) in particles by passing them through an intense laser beam. The laser light heats EC in particles causing them to vaporize in the beam. Detection of wavelength-resolved thermal radiation emissions provides quantitative information on the EC mass of individual particles in the size range of 0.2–1 μm diameter. Non-absorbing particles are sized based on the amount of light they scatter from the laser beam. The time series of the scattering signal of a non-absorbing particle is a Gaussian, because the SP2 laser is in the TEM00 mode. Information on the scattering properties of externally and internally mixed EC particles as detected by the SP2 is lost in general, because each particle changes size, shape, and composition as it passes through the laser beam. Thus, scattered light from a sampled EC particle does not yield a full Gaussian waveform. A method for determining the scattering properties of EC particles using a two-element avalanche photodiode (APD) is described here. In this method, the Gaussian scattering function is constructed from the leading edge of the scattering signal (before the particle is perturbed by the laser), the Gaussian width, and the location of the leading edge in the beam derived from the two-element APD signal. The method allows an SP2 to determine the scattering properties of individual EC particles as well as the EC mass. Detection of polystyrene latex spheres, well-characterized EC particles with and without organic coatings, and Mie scattering calculations are used to validate the method.

New photolysis system for NO2 measurements in the lower stratosphere

A new system for NO2 detection has been developed for use on the NASA ER-2 aircraft. The system converts NO2 to NO using UV photolysis with the NO product subsequently detected with an on-board chemiluminescence detector. The new system is compact, light weight, has high time resolution (- 1 s), and is significantly more efficient then some previous designs. Details of the system design and airborne performance are discussed.

A fast-response chemical ionization mass spectrometer for in situ measurements of HNO3 in the upper troposphere and lower stratosphere

A chemical ionization mass spectrometer instrument has been developed for in situ measurements of nitric acid (HNO3) in the upper troposphere and lower stratosphere from the NASA WB-57 aircraft. Fast and sensitive measurements of HNO3 are achieved by using a low surface area heated Teflon sampling inlet and detection techniques that employ ion-molecule reactions. Sensitivity to HNO3 is determined in flight by adding HNO3 from a calibrated HNO3 permeation source into the sample air flow, and instrument background is measured by displacing ambient air from the sampling inlet with a flow of dry nitrogen in the sampling inlet. Instrument temperatures, pressures, and gas flows are controlled in flight to maintain a constant detection sensitivity in a changing ambient operating environment. The initial performance of this new instrument is evaluated using HNO3 and ozone data obtained between 6 and 19 km during the 1999 NASA Atmospheric Chemistry of Combustion Emissions Near the Tropopause mission. The data reve...

Exchange between the upper tropical troposphere and the lower stratosphere studied with aircraft observations

Exchange between the upper tropical troposphere and the lower stratosphere is considered by examining WB57F and ER-2 aircraft observations of water, ozone, wind, and temperature in the potential temperature range 360 < θ < 420 K. These processes are examined in part by using the technique of unified scale invariance on the airborne data, as has been done previously for the lower stratospheric polar vortex. Scale invariance is found, on scales from a few hundred meters to the maximum flown, 2700 km (25 great circle degrees). The results apply both to vertical exchange at the tropical tropopause and to isentropic exchange at the subtropical jet stream. All scales participate in the maintenance of the mean state, with substantial contributions from relatively infrequent but intense events in the long tails of the probability distributions. Past data are examined and found to fit this general framework. A unique mapping of tropical tropopause temperature to the total hydrogen content of the middleworld and overworld should not be expected; the head of the tape recorder is at 50-60 hPa rather than 90-100 hPa. The tropical tropopause is observed at potential temperatures θ T greater than the maximum moist static surface values θ W , such that θ T - θ W varies between 10 K in fall and up to 40 K in spring. The meridional gradient of θ T is directed from the subtropical jet stream to the inner tropics, with θ T declining by approximately 10 K from near 30°N to near 10°N in the vicinity of 95°W. The maintenance of these θ T values is discussed. Total water (measured as the sum of vapor and vaporized ice) and ozone, major absorbers of solar radiation and emitters/ absorbers of terrestrial infrared radiation, show scale invariance in the upper tropical troposphere. The implications of this result for the notion of a conservative cascade of energy via fluid dynamics from the largest to the smallest scales are discussed. The scaling exponents H z for total water and ozone in the upper tropical troposphere are not the value, 5/9, expected for a passive scalar, probably indicating the presence of sources and/or sinks operating faster than mixing.

Balloon‐borne stratospheric grab‐sampling system

A lightweight balloon‐borne grab‐sampling system for determining mixing ratios <10−9 of chlorocarbons and other minor constituents in the stratosphere is described. The all‐metal system consists of five sampling spheres and associated valves, which are opened and closed at selected altitudes by on‐board electronics during a parachute descent. The construction features, operating techniques, and experimental tests are given. In the latter, particular attention has been given to the problem of surface adsorption in ambient‐pressure in situ sampling of trace stratospheric constituents at these low mixing ratios.

Chlorine activation near the midlatitude tropopause

wave activity, high particulate surface areas (5–20 mm 2 cm �3 ), low ozone, and relatively high humidities (20–25 ppm of H2O, yet undersaturated with respect to ice), consistent with a heterogeneous mechanism on particles formed in recently lofted tropospheric air as it mixed into the lowermost stratosphere. These observations are similar to a previous one of chlorine activation on volcanic aerosol, suggesting a common heterogeneous chemical mechanism involving HCl, ClNO3, and HOCl that even in volcanically quiescent years can impact ozone photochemistry in regions of the lowermost stratosphere influenced by mixing from the tropopause region. Models not incorporating this chlorine activation process may be underestimating the impact on ozone in the midlatitude lowermost stratosphere by decomposition of very short lived halocarbon compounds, including substitutes for ozone-depleting compounds.

A Chemical Ionization Mass Spectrometer for Ground-Based Measurements of Nitric Acid

Abstract A chemical ionization mass spectrometer (CIMS) instrument has been developed for high-precision measurements of gaseous nitric acid (HNO3) specifically under high- and variable-humidity conditions in the boundary layer. The instrument’s background signals (i.e., signals detected when HNO3-free air is measured), which depend on the humidity and HNO3 concentration of the sample air, are the most important factor affecting the limit of detection (LOD). A new system to provide HNO3-free air without changing both the humidity and the pressure of the sampled air was developed to measure the background level accurately. The detection limit was about 23 parts per trillion by volume (pptv) for 50-s averages. Field tests, including an intercomparison with the diffusion scrubber technique, were carried out at a surface site in Tokyo, Japan, in October 2003 and June 2004. A comparison between the measured concentrations of HNO3 and particulate nitrate indicated that the interference from particulate nitrate ...

An Electrostatic-Wave Topside Sounder

An electrostatic-wave topside sounder has been flown to study electron plasma resonances. Unique features of this sounder are the preservation of data spectra, a frequency synthesizer, and a gain-change mechanism. Preservation of the spectra provided frequency information with a resolution of a few hundred hertz by use of a fast Fourier transform while the synthesizer provided the necessary frequency stability. The gain-change mechanism provided information on the strength of the resonances. Resulting data support the electrostatic-wave echo theory of topside resonances.

Correction to “Nitric acid uptake on subtropical cirrus cloud particles”

Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA. Also at Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA. Institut fur Physik der Atmosphare, Deutsches Zentrum fur Luftand Raumfahrt Oberpfaffenhofen, Wessling, Germany. Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA. Universidad Nacional Autonoma de Mexico, Centro de Ciencias de la Atmosfera, Ciudad Universitaria, Mexico City, Mexico. Department of Meteorology, University of Utah, Salt Lake City, Utah, USA. Atmospheric Research Project, Harvard University, Cambridge, Massachusetts, USA. Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, California, USA. Now at Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, New York, USA. NASA Ames Research Center, Moffett Field, California, USA. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D08306, doi:10.1029/2004JD004781, 2004