Jeremy J. Harrison

Growth in stratospheric chlorine from short‐lived chemicals not controlled by the Montreal Protocol

Abstract We have developed a chemical mechanism describing the tropospheric degradation of chlorine containing very short‐lived substances (VSLS). The scheme was included in a global atmospheric model and used to quantify the stratospheric injection of chlorine from anthropogenic VSLS ( ClyVSLS) between 2005 and 2013. By constraining the model with surface measurements of chloroform (CHCl3), dichloromethane (CH2Cl2), tetrachloroethene (C2Cl4), trichloroethene (C2HCl3), and 1,2‐dichloroethane (CH2ClCH2Cl), we infer a 2013 ClyVSLS mixing ratio of 123 parts per trillion (ppt). Stratospheric injection of source gases dominates this supply, accounting for ∼83% of the total. The remainder comes from VSLS‐derived organic products, phosgene (COCl2, 7%) and formyl chloride (CHClO, 2%), and also hydrogen chloride (HCl, 8%). Stratospheric ClyVSLS increased by ∼52% between 2005 and 2013, with a mean growth rate of 3.7 ppt Cl/yr. This increase is due to recent and ongoing growth in anthropogenic CH2Cl2—the most abundant chlorinated VSLS not controlled by the Montreal Protocol.

Measurement of the Magnetic Properties of FeH in Its X4Δ and F4Δ States from Sunspot Spectra

The spin-rotational levels of FeH in its F4Δ and X4Δ states are significantly perturbed by nearby electronic states. As a result, it is not possible to make reliable calculations of its magnetic dipole moments from a simple effective Hamiltonian. In this paper, we report experimental measurements of the magnetic dipole moments of FeH in several rotational levels of the two lowest spin components of the v = 0 levels of both the F4Δ and X4Δ states. The observational data are taken from the Sunspot Spectral Atlas of Wallace et al.; the local magnetic flux densities are determined from the splittings of atomic lines present in the spectrum. These results considerably extend the range of known magnetic dipole moments for FeH and provide many lines in the F4Δ–X4Δ transition at 990 nm (the Wing-Ford system) for astronomers to use for the measurement of the local magnetic fields of cool stars where suitable atomic lines are not available for this purpose.

ACE-FTS observations of acetonitrile in the lower stratosphere

Abstract. This work reports the first infrared satellite remote-sensing measurements of acetonitrile (CH 3 CN) in the Earths atmosphere using solar occultation measurements made by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) between 2004 and 2011. The retrieval scheme uses new quantitative laboratory spectroscopic measurements of acetonitrile (Harrison and Bernath, 2012). Although individual ACE-FTS profile measurements are dominated by measurement noise, median profiles in 10° latitude bins show a steady decline in volume mixing ratio from ~150 ppt (parts per trillion) at 11.5 km to

New and improved infrared absorption cross sections for dichlorodifluoromethane (CFC-12)

Despite its widespread commercial use throughout the twentieth century, primarily in the refrigeration industry, dichlorodifluoromethane (CFC-12) is now known to have the undesirable effect of depleting stratospheric ozone. As this long-lived molecule slowly degrades in the atmosphere, monitoring its vertical concentration profile using infrared sounders on satellite platforms crucially requires accurate laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of dichlorodifluoromethane over the spectral range 800–1270 cm, determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm pathlength cell. Spectra of dichlorodifluoromethane/dry synthetic air mixtures were recorded at resolutions between 0.01 and 0.03 cm (calculated as 0.9/MOPD; MOPD=maximum optical path difference) over a range of temperatures and pressures (7.5–761 Torr and 190–294 K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN and GEISA databases.

Magnetic circular dichroism and absorption spectra of methylidyne in a krypton matrix.

Electronic absorption and magnetic circular dichroism spectra are reported for the A(2)Δ, B(2)Σ(-), and C(2)Σ(+) ← X(2)Π transitions of methylidyne radicals isolated in a Kr matrix at cryogenic temperatures. The results are interpreted in the framework of a model in which the X(2)Π term is split by combination of spin-orbit and crystal-field interactions with the atoms of the host matrix. Analysis of the zeroth moments of the spectra yields an empirical spin-orbit coupling constant A(Π) = 11 ± 2 cm(-1) and orbital reduction factor κ = 0.26 ± 0.05, corresponding to a crystal-field splitting of V(Π) = 43 ± 10 cm(-1) for the X(2)Π term. For the A(2)Δ excited-state term, analysis of the first MCD moments gives a spin-orbit coupling constant of A(Δ) = 4.4 ± 0.9 cm(-1).

Atmospheric Chemistry Experiment (ACE): Detecting Trace Organic Compounds from Orbit

We highlight recent laboratory spectroscopic measurements of organic molecules made in support of the ACE mission, and preliminary retrievals from ACE spectra.