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Ground-based observations of 11.072 GHz atmospheric ozone (O3) emission have been made using the Ny-Ålesund Ozone in the Mesosphere Instrument (NAOMI) at the UK Arctic Research Station (latitude 78∘55′0′′ N, longitude 11∘55′59′′ E), Spitsbergen. Seasonally averaged O3 vertical profiles in the Arctic polar mesosphere–lower thermosphere region for night-time and twilight conditions in the period 15 August 2017 to 15 March 2020 have been retrieved over the altitude range 62–98 km. NAOMI measurements are compared with corresponding, overlapping observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. The NAOMI and SABER version 2.0 data are binned according to the SABER instrument 60 d yaw cycles into nominal 3-month “winter” (15 December–15 March), “autumn” (15 August–15 November), and “summer” (15 April–15 July) periods. The NAOMI observations show the same year-to-year and seasonal variabilities as the SABER 9.6 µm O3 data. The winter night-time (solar zenith angle, SZA ≥ 110∘) and twilight (75∘ ≤ SZA ≤ 110∘) NAOMI and SABER 9.6 µm O3 volume mixing ratio (VMR) profiles agree to within the measurement uncertainties. However, for autumn twilight conditions the SABER 9.6 µm O3 secondary maximum VMR values are higher than NAOMI over altitudes 88–97 km by 47 % and 59 %, respectively in 2017 and 2018. Comparing the two SABER channels which measure O3 at different wavelengths and use different processing schemes, the 9.6 µm O3 autumn twilight VMR data for the three years 2017–2019 are higher than the corresponding 1.27 µm measurements with the largest difference (58 %) in the 65–95 km altitude range similar to the NAOMI observation. The SABER 9.6 µm O3 summer daytime (SZA < 75∘) mesospheric O3 VMR is also consistently higher than the 1.27 µm measurement, confirming previously reported differences between the SABER 9.6 µm channel and measurements of mesospheric O3 by other satellite instruments.

Ground based observations of 11.072 GHz atmospheric ozone (O3) emission have been made using the Ny Ålesund Ozone in the Mesosphere Instrument (NAOMI) at the UK Arctic Research Station (latitude 78°55’0” N, longitude 11°55’59” E), Spitsbergen. Seasonally averaged O3 vertical profiles in the Arctic polar mesosphere lower thermosphere region for night-time and twilight conditions in the period 15 August 2017 to 15 March 2020 have been retrieved over the altitude range 62–98 km. NAOMI measurements are compared with corresponding, overlapping observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. The NAOMI and SABER data are binned according to the SABER instrument 60 day yaw cycles into 3 month ‘winter’ (15 December–15 March), ‘autumn’ (15 August–15 November), and ‘summer’ (15 April–15 July) periods. The NAOMI observations show the same year-to-year and seasonal variabilities as the SABER 9.6 μm O3 data. The winter night-time (solar zenith angle, SZA ≥ 110°) and twilight (75° ≤ SZA ≤ 110°) NAOMI and SABER 9.6 μm O3 volume mixing ratio (VMR) profiles agree to within the measurement uncertainties. However, for autumn twilight conditions the SABER 9.6 μm O3 secondary maximum VMR values are higher than NAOMI over altitudes 88–97 km by 47 % and 59 % respectively in 2017 and 2018. Comparing the two SABER channels which measure O3 at different wavelengths and use different processing schemes, the 9.6 μm O3 autumn twilight VMR data for the three years 2017–19 are higher than the corresponding 1.27 μm measurements with the largest difference (58 %) in the 65–95 km altitude range similar to the NAOMI observation. The SABER 9.6 μm O3 summer daytime (SZA 3 VMR is also consistently higher than the 1.27 μm measurement, confirming previously reported differences between the SABER 9.6 μm channel and measurements of mesospheric O3 by other satellite instruments.

Diurnal very low frequency (VLF) sub‐ionospheric radiowave phase measurements show a night‐to‐day transition pattern. During this sunrise transition a phase perturbation, which consist of a phase overshoot followed by a small phase recovery to normal daytime values, is often observed. The variability of the size of this sunrise phase perturbation, and its maximum and end times were monitored to identify the associated physical causes. VLF signal from the 22.1 kHz UK transmitter (call sign GVT) recorded at Sodankylä, Finland, from 20 April 2010 until 31 December 2016 were used. The timing at the maximum of the phase perturbation period, has an annual pattern that is well described by the seasonal variation of the sunrise time 28 km above the transmitter. Variations in ozone number density at 38–42 km altitudes are better correlated (R = 0.7) with the sunrise phase perturbation variability than at any other altitudes below ~80 km, and exhibit higher correlation values than for atmospheric temperature. Our results show that the main characteristics of the observed VLF sunrise phase perturbation arise from shadowing of short wavelength solar UV flux from the D‐region ionosphere due to stratospheric ozone absorption.

The Ku-band microwave frequencies (10.70–14.25 GHz) overlap emissions from ozone (O3) at 11.072 GHz and hydroxyl radical (OH) at 13.441 GHz. These important chemical species in the polar middle atmosphere respond strongly to high-latitude geomagnetic activity associated with space weather. Atmospheric model calculations predict that energetic electron precipitation (EEP) driven by magnetospheric substorms produces large changes in polar mesospheric O3 and OH. The EEP typically peaks at geomagnetic latitudes of ∼65∘ and evolves rapidly with time longitudinally and over the geomagnetic latitude range 60–80∘. Previous atmospheric modelling studies have shown that during substorms OH abundance can increase by more than an order of magnitude at 64–84 km and mesospheric O3 losses can exceed 50 %. In this work, an atmospheric simulation and retrieval study has been performed to determine the requirements for passive microwave radiometers capable of measuring diurnal variations in O3 and OH profiles from high-latitude Northern Hemisphere and Antarctic locations to verify model predictions. We show that, for a 11.072 GHz radiometer making 6 h spectral measurements with 10 kHz frequency resolution and root-mean-square baseline noise of 1 mK, O3 could be profiled over 8×10-4–0.22 hPa (∼98–58 km) with 10–17 km height resolution and ∼1 ppmv uncertainty. For the equivalent 13.441 GHz measurements with vertical sensor polarisation, OH could be profiled over 3×10-3–0.29 hPa (∼90–56 km) with 10–17 km height resolution and ∼3 ppbv uncertainty. The proposed observations would be highly applicable to studies of EEP, atmospheric dynamics, planetary-scale circulation, chemical transport, and the representation of these processes in polar and global climate models. Such observations would provide a relatively low-cost alternative to increasingly sparse satellite measurements of the polar middle atmosphere, extending long-term data records and also providing “ground truth” calibration data.

Energetic electron precipitation leads to increased nitric oxide (NO) production in the mesosphere and lower thermosphere. NO distributions in the wintertime, high‐latitude Southern Hemisphere atmosphere during geomagnetic storms are investigated. NO partial columns in the upper mesosphere at altitudes 70–90 km and in the lower thermosphere at 90–110 km have been derived from observations made by the Solar Occultation For Ice Experiment (SOFIE) on board the Aeronomy of Ice in the Mesosphere (AIM) satellite. The SOFIE NO measurements during 17 geomagnetic storms in 2008–2014 have been binned into selected geomagnetic latitude and geographic latitude/longitude ranges. The regions above Antarctica showing the largest instantaneous NO increases coincide with high fluxes of 30–300 keV precipitating electrons from measurements by the second‐generation Space Environment Monitor (SEM‐2) Medium Energy Proton and Electron Detector (MEPED) instrument on the Polar‐orbiting Operational Environmental Satellites (POES). Significant NO increases over the Antarctic Peninsula are likely due to precipitation of >30 keV electrons from the radiation belt slot region. NO transport is estimated using Horizontal Wind Model (HWM14) calculations. In the upper mesosphere strong eastward winds (daily mean zonal wind speed ~20–30 m s−1 at 80 km) during winter transport NO‐enriched air away from source regions 1–3 days following the storms. Mesospheric winds also introduce NO‐poor air into the source regions, quenching initial NO increases. Higher up, in the lower thermosphere, weaker eastward winds (~5–10 m s−1 at 100 km) are less effective at redistributing NO zonally.

The submillimetre is an understudied region of the Earth's atmospheric electromagnetic spectrum. Prior technological gaps and relatively high opacity due to the prevalence of rotational water vapour lines at these wavelengths have slowed progress from a ground-based remote sensing perspective; however, emerging superconducting detector technologies in the fields of astronomy offer the potential to address key atmospheric science challenges with new instrumental methods. A site study, with a focus on the polar regions, is performed to assess theoretical feasibility by simulating the downwelling (zenith angle = 0°) clear-sky submillimetre spectrum from 30 mm (10 GHz) to 150 µm (2000 GHz) at six locations under annual mean, summer, winter, daytime, night-time and low-humidity conditions. Vertical profiles of temperature, pressure and 28 atmospheric gases are constructed by combining radiosonde, meteorological reanalysis and atmospheric chemistry model data. The sensitivity of the simulated spectra to the choice of water vapour continuum model and spectroscopic line database is explored. For the atmospheric trace species hypobromous acid (HOBr), hydrogen bromide (HBr), perhydroxyl radical (HO2) and nitrous oxide (N2O) the emission lines producing the largest change in brightness temperature are identified. Signal strengths, centre frequencies, bandwidths, estimated minimum integration times and maximum receiver noise temperatures are determined for all cases. HOBr, HBr and HO2 produce brightness temperature peaks in the mK to µK range, whereas the N2O peaks are in the K range. The optimal submillimetre remote sensing lines for the four species are shown to vary significantly between location and scenario, strengthening the case for future hyperspectral instruments that measure over a broad wavelength range. The techniques presented here provide a framework that can be applied to additional species of interest and taken forward to simulate retrievals and guide the design of future submillimetre instruments.

The subionospheric very low frequency (VLF) radio wave technique provides the possibility of investigating the response of the ionospheric D‐region to a diversity of transient and long‐term physical phenomena originating from above (e.g., energetic particle precipitation) and from below (e.g., atmospheric waves). In this study, we identify the periodicities that appear in VLF measurements and investigate how they may be related to changes in space weather and atmospheric activity. The powerful VLF signal transmitted from NAA (24 kHz) on the east coast of the USA, and received at Sodankylä, Finland, was analyzed. Wavelet transform, wavelet power spectrum, wavelet coherence, and cross‐wavelet spectrum were computed for daily averages of selected ionospheric, space weather, and atmospheric parameters from November 2008 until June 2018. Our results show that the significant VLF periods that appear during solar cycle 24 are the annual oscillation (AO), semiannual oscillation (SAO), 121‐day, 86‐day, 61‐day, and solar rotation oscillations. We found that the AO corresponds to variability in mesospheric temperature and solar Lyman‐α (Ly‐α) flux and the SAO to variability in space weather‐related parameters. The solar rotation oscillation observed in the VLF variability is mainly related to the Ly‐α flux variation at solar maximum, and to geomagnetic activity variation during the declining phase of the solar cycle. Our results are important since they strengthen our understanding of the Earth's D‐region response to solar and atmospheric forcing.

The Ku-band microwave frequencies (10.70–14.25 GHz) overlap emissions from ozone (O3) at 11.072 GHz and hydroxyl radical (OH) at 13.441 GHz. These important chemical species in the polar middle atmosphere respond strongly to high latitude geomagnetic activity associated with space weather. Atmospheric model calculations predict that energetic electron precipitation (EEP) driven by magnetospheric sub storms produces large changes in polar mesospheric O3 and OH. The EEP typically peaks at geomagnetic latitudes ~ 65° and evolves rapidly with time longitudinally and over the geomagnetic latitude range 60°–80°. Previous atmospheric modelling studies have shown that during sub storms OH abundance can increase by more than an order of magnitude at 64–84 km and mesospheric O3 losses can exceed 50 %. In this work, an atmospheric simulation and retrieval study has been performed to determine the requirements for passive microwave radiometers capable of measuring diurnal variations in O3 and OH profiles from high latitude northern hemisphere and Antarctic locations to verify model predictions. We show that, for a 11.072 GHz radiometer making 6 h spectral measurements with 10 kHz frequency resolution and root mean square baseline noise of 1 mK, O3 could be profiled over 8 × 10−4–0.22 hPa (~ 98–58 km) with 10–17 km height resolution and ~ 1 ppmv uncertainty. For the equivalent 13.441 GHz measurements with vertical sensor polarisation, OH could be profiled over 3 × 10−3–0.29 hPa (~ 90–56 km) with 10–17 km height resolution and ~ 3 ppbv uncertainty. The proposed observations would be highly applicable to studies of EEP, atmospheric dynamics, planetary scale circulation, chemical transport, and the representation of these processes in polar and global climate models. Such observations would provide a relatively low cost alternative to increasingly sparse satellite measurements of the polar middle atmosphere, extending long-term data records and also providing ground truth calibration data.

Meteorological and atmospheric models are being extended up to 80 km altitude but there are very few observing techniques that can measure stratospheric–mesospheric winds at altitudes between 20 and 80 km to verify model datasets. Here we demonstrate the feasibility of horizontal wind profile measurements using ground-based passive millimetre-wave spectroradiometric observations of ozone lines centred at 231.28, 249.79, and 249.96 GHz. Vertical profiles of horizontal winds are retrieved from forward and inverse modelling simulations of the line-of-sight Doppler-shifted atmospheric emission lines above Halley station (75°37′ S, 26°14′ W), Antarctica. For a radiometer with a system temperature of 1400 K and 30 kHz spectral resolution observing the ozone 231.28 GHz line we estimate that 12 h zonal and meridional wind profiles could be determined over the altitude range 25–74 km in winter, and 28–66 km in summer. Height-dependent measurement uncertainties are in the range 3–8 m s−1 and vertical resolution ∼ 8–16 km. Under optimum observing conditions at Halley a temporal resolution of 1.5 h for measuring either zonal or meridional winds is possible, reducing to 0.5 h for a radiometer with a 700 K system temperature. Combining observations of the 231.28 GHz ozone line and the 230.54 GHz carbon monoxide line gives additional altitude coverage at 85 ± 12 km. The effects of clear-sky seasonal mean winter/summer conditions, zenith angle of the received atmospheric emission, and spectrometer frequency resolution on the altitude coverage, measurement uncertainty, and height and time resolution of the retrieved wind profiles have been determined.

Nitric oxide (NO) produced in the polar middle and upper atmosphere by energetic particle precipitation depletes ozone in the mesosphere and, following vertical transport in the winter polar vortex, in the stratosphere. Medium‐energy electron (MEE) ionization by 30–1,000 keV electrons during geomagnetic storms may have a significant role in mesospheric NO production. However, questions remain about the relative importance of direct NO production by MEE at altitudes ~60–90 km versus indirect NO originating from auroral ionization above 90 km. We investigate potential drivers of NO variability in the southern‐hemisphere mesosphere and lower thermosphere during 2013–2014. Contrasting geomagnetic activity occurred during the two austral winters, with more numerous moderate storms in the 2013 winter. Ground‐based millimeter‐wave observations of NO from Halley, Antarctica, are compared with measurements by the Solar Occultation For Ice Experiment (SOFIE) spaceborne spectrometer. NO partial columns over the altitude range 65–140 km from the two observational data sets show large day‐to‐day variability and significant disagreement, with Halley values on average 49% higher than the corresponding SOFIE data. SOFIE NO number densities, zonally averaged over geomagnetic latitudes −59° to −65°, are up to 3 × 108/cm3 higher in the winter of 2013 compared to 2014. Comparisons with a new version of the Whole Atmosphere Community Climate Model, which includes detailed D‐region ion chemistry (WACCM‐SIC) and MEE ionization rates, show that the model underestimates NO in the winter lower mesosphere whereas thermospheric abundances are too high. This indicates the need to further improve and verify WACCM‐SIC with respect to MEE ionization, thermospheric NO chemistry, and vertical transport.

Magnetospheric substorms drive energetic electron precipitation into the Earth's atmosphere. We use the output from a substorm model to describe electron precipitation forcing of the atmosphere during an active substorm period in April–May 2007. We provide the first estimate of substorm impact on the neutral composition of the polar middle atmosphere. Model simulations show that the enhanced ionization from a series of substorms leads to an estimated ozone loss of 5–50% in the mesospheric column depending on season. This is similar in scale to small to medium solar proton events (SPEs). This effect on polar ozone balance is potentially more important on long time scales (months to years) than the impulsive but sporadic (few SPE/year versus three to four substorms/day) effect of SPEs. Our results suggest that substorms should be considered an important source of energetic particle precipitation into the atmosphere and included in high-top chemistry-climate models.

[1] We report ground-based measurements of the polar middle atmosphere made using a 230–250 GHz passive microwave radiometer deployed at Troll station (72°01′S 02°32′E, L shell of L = 4.8), Antarctica. Our observations show enhanced mesospheric nitric oxide (NO) volume mixing ratio (VMR) during a series of small recurrent geomagnetic storms in the 2008 austral winter, reaching 1.2 ppmv on day 200 (18 July). The Lomb normalized periodogram of the NO VMR time series averaged over 65-80 km for days 130 to 220 of 2008 (9 May to 7 August) shows a peak exceeding the 95% confidence limit at 25.8 days, close to the synodic rotation period for low-latitude solar coronal holes. The highest correlations between the radiometer NO VMR data and trapped and quasi-trapped electron count rates for L = 3.5-5.5 from the Polar Orbiting Environment Satellites 90° telescope are for the >30 keV (90e1) channel (rmax = 0.56, lag time of 5.1 days) and >100 keV (90e2) channel (rmax = 0.57, lag time of 4.4 days). Maximum correlation between NO VMR and the >700 keV (90P6) channel data is lower but lag times are close to zero. Superposed epoch analyses for the eight most significant geomagnetic storm periods and three Carrington rotations (2070-2072) within the 90 day observation period indicate that significant NO abundance observed at 65-80 km in the Antarctic mesosphere may be produced directly by >200 keV electron precipitation or originate from a source at higher altitudes, e.g., production by >30 keV electrons followed by downward transport.

This study presents a new ion–neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D-region (altitudes ∼ 50–90 km) chemistry is based on the Sodankylä Ion Chemistry (SIC) model, a one-dimensional model containing 307 ion–neutral and ion recombination, 16 photodissociation and 7 photoionization reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the simulation error minimization connectivity method (SEM-CM) to produce a reaction scheme of 181 ion–molecule reactions of 181 ion–molecule reactions of 27 positive and 18 negative ions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3−, NO2−, O−, O2, OH−, O2−(H2O), O2−(H2O)2, O4−, CO3−, CO3−(H2O), CO4−, HCO3−, NO2−, NO3−, NO3−(H2O), NO3−(H2O)2, NO3−(HNO3), NO3−(HNO3)2, Cl−, ClO−), which agree with the full SIC mechanism within a 5 % tolerance. Four 3-D model simulations were then performed, using the impact of the January 2005 solar proton event (SPE) on D-region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM method). The standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion–molecule reactions that affect the partitioning of odd nitrogen (NOx), odd hydrogen (HOx) and O3 in the stratosphere and mesosphere.

This study presents a new ion-neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D region (altitudes ~ 50–90 km) chemistry is based on the Sodankylä Ion and Neutral Chemistry (SIC) model, a 1-dimensional model containing 306 ion-neutral and ionrecombination reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the Simulation Error Minimization Connectivity Method (SEM-CM) to produce a reaction scheme of 181 ion-molecule reactions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3−, NO2−, O−, O2, OH−, O2−(H2O), O2−(H2O)2, O4−, CO3−, CO3−(H2O), CO4−, HCO3−, NO2−, NO3−, NO3−(H2O), NO3(H2O)2, NO3−(HNO3), NO3−(HNO3)2, Cl−, ClO−), which agree with the full SIC mechanism within a 5 % tolerance. Four 3D model simulations were then performed, using the impact of the January 2005 Solar Proton Event (SPE) on D region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM Method). Standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion-molecule reactions that affect the partitioning of odd nitrogen (NOx), odd hydrogen (HOx), and O3 in the stratosphere and mesosphere.

Meteorological and atmospheric models are being extended up to 80 km altitude but there are very few observing techniques that can measure stratospheric-mesospheric winds at altitudes between 20 km and 80 km to verify model data-sets. Here we demonstrate the feasibility of horizontal wind profile measurements using ground-based passive millimetre-wave spectroradiometric observations of ozone lines centred at 231.28 GHz, 249.79 GHz, and 249.96 GHz. Vertical profiles of horizontal winds are retrieved from forward and inverse modelling simulations of the line-of-sight Doppler-shifted atmospheric emission lines above Halley station (75°37’S, 26°14’W), Antarctica. For a radiometer with a system temperature of 1400 K and 30 kHz spectral resolution observing the ozone 231.28 GHz line we estimate that 12hr zonal and meridional wind profiles could be determined over the altitude range 25–74 km in winter, and 28–66 km in summer. Height-dependent measurement uncertainties are in the range 3–8 m s–1 and vertical resolution ~8–16 km. Under optimum observing conditions at Halley a temporal resolution of 1.5hrs for measuring either zonal or meridional winds is possible, reducing to 0.5hr for a radiometer with a 700 K system temperature. Combining observations of the 231.28 GHz ozone line and the 230.54 GHz carbon monoxide line gives additional altitude coverage at 85±12 km. The effects of clear-sky seasonal mean winter/summer conditions, zenith angle of the received atmospheric emission, and spectrometer frequency resolution on the altitude coverage, measurement uncertainty, and height and time resolution of the retrieved wind profiles have been determined.

Delayed release dosage forms such as Asacol employ coatings that are engineered to breakdown and release the drug topically at the nominal pH of the lower intestinal tract. Asacol tablets were found to dissolve in an erratic fashion when they are dissolved in buffers below pH 7 which can occur naturally. In this study Terahertz pulsed imaging (TPI) was used to accurately map the coating thickness of a group of Asacol tablets that were subsequently dissolved using the USP method at pH 6.8. The mean dissolution times were found to correlate with the average coating thickness measured over all surfaces. Thickness values for a single randomly selected face did not correlate well with the dissolution results. The speed and ease of TPI mapping may make it an attractive replacement for wet dissolution testing both in product development and eventually for process analysis.

Pulsed terahertz attenuated total reflection (ATR) spectra of solid materials and liquids covering the 10 cm−1 to 120 cm−1 (0.3 THz to 3.6 THz) region of the electromagnetic spectrum are recorded using a terahertz pulsed spectrometer and silicon ATR modules. Pulsed terahertz ATR measurements are completed nondestructively using small amounts of sample (typically 1 mg for solids) and no sample preparation. Many terahertz analyses can be run in rapid sequence, minimizing the analysis time.

In this study for the first time temperature dependent terahertz pulsed spectroscopy was performed on a pharmaceutical drug. The polymorphic conversion process of carbamazepine form III to I was studied at varying temperatures. Furthermore, the solid-state transformation at isothermal conditions below the melting point of carbamazepine was investigated. The ability to study solid-state reactions with terahertz pulsed spectroscopy could be demonstrated.

In this paper, we present the latest chemical mapping images of heterogeneous mixtures based on far-infrared reflection spectra obtained using a terahertz pulsed imaging system. The terahertz images and spectral data obtained have a spectral resolution of 1 cm−1 and cover a spectral range of 5–80 cm−1. This broad spectral coverage enables us to map out the spatial distribution of individual chemical components of a sample in a single measurement.

The application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated. The different polymorphic forms of carbamazepine and enalapril maleate exhibit distinct terahertz absorbance spectra. In contrast to crystalline indomethacin and fenoprofen calcium, amorphous indomethacin and liquid crystalline fenoprofen calcium show no absorption modes, which is likely to be due to a lack of order. These findings suggest that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations. The large spectral differences between different forms of the compounds studied is evidence that terahertz pulsed spectroscopy is well-suited to distinguishing crystallinity differences in pharmaceutical compounds.

This paper describes the stratospheric and mesospheric ozone profiles retrieved from spectral measurements of the 249.96 GHz O3 line, using the British Antarctic Survey's ground-based Microwave Radiometer at Troll (BAS-MRT), Antarctica (72°01' S, 02°32' E, 62° Mlat). The instrument operated at Troll from February 2008 through January 2010, and hourly averaged spectra were used to retrieve approximately 20 ozone profiles per day. The ozone profiles cover the pressure range from 3 hPa to 0.02 hPa (approximately 38 to 72 km) which includes the topside of the stratospheric ozone layer and the peak of the tertiary maximum. Comparing the retrieved ozone volume mixing ratio (vmr) values to Aura/MLS and SD-WACCM shows no significant bias to within the instrumental uncertainties. The long-term variations (>20 days) between MLS and SD-WACCM agree well with BAS-MRT at all altitudes with significant correlation coefficients of at least 0.9 (0.7 with SD-WACCM) in the upper stratosphere and middle mesosphere. A weaker correlation is found for the long-term variations in summer when most of the vmr values are below the random noise level of Aura/MLS. The correlation of short-term variations (

The electric-dipole forbidden a1Δg − X3 (0,0) band of gas-phase O2 has been studied in absorption at wavelengths around 1.27 μm using Fourier transform spectroscopy and a long-path absorption cell. Experiments were conducted at temperatures of 294, 243, and 200 K and at pressures in the range 140−750 Torr. Both pure O2 and a mixture of 21% O2/79% N2 were studied, and line widths, integrated line intensities, and integrated absorption intensities (AIs) for the (0,0) vibrational band were measured. Integrated AIs were found to be independent of temperature, pressure, and gas composition, and the recommended value for the vibrational band from the current study is Sint = 3.210(15) × 10-24 cm molecule-1 (1σ error) for pure 16O2, corresponding to an Einstein A-coefficient of A = 2.256(10) × 10-4 s-1. The effect of including other oxygen isotopomers is to increase the integrated AI value for this origin band to Sint = 3.226(15) × 10-24 cm molecule-1. Widths of individual spectroscopic lines decrease with increa...

Absorption spectra of gas-phase molecular oxygen and zero air at temperatures of 223 and 283 K have been measured in the laboratory using a coolable multipass-optics gas cell and Fourier transform spectroscopy in the wavelength range 455 to 830 nm (12,000-22,000 cm -1 ). Net absorption cross sections of the O 2 A-, B-, and γ-bands at

[1] Using a ground-based microwave radiometer at Troll Station, Antarctica (72°S, 2.5°E,L = 4.76), we have observed a decrease of 20–70% in the mesospheric ozone, coincident with increased nitric oxide, between 60 km and 75 km altitude associated with energetic electron precipitation (E > 30 keV) during a moderate geomagnetic storm (minimum Dst of −79 nT) in late July 2009. NOAA satellite data were used to identify the precipitating particles and to characterize their energy, spatial distribution and temporal variation over Antarctica during this isolated storm. Both the ozone decrease and nitric oxide increase initiate with the onset of the storm, and persist for several days after the precipitation ends, descending in the downward flow of the polar vortex. These combined data present a unique case study of the temporal and spatial morphology of chemical changes induced by electron precipitation during moderate geomagnetic storms, indicating that these commonplace events can cause significant effects on the middle mesospheric ozone distribution.

A laser-ablated pulsed beam of Mn atoms, in various long-lived states, has been employed to determine excitation functions for the reactions Mn + SnCl4 → MnCl* ("blue," "green," "red") + SnCl3. The data all show a sharp rise at low energies, followed by an equally rapid fall, but they differ in the initial thresholds and the rate at which σ(ET) approaches zero. Analysis in terms of a multiple line-of-centres model (Levy, Res. Chem. Kinet. 1, 163 (1993)) indicates that each excitation function is unique, and is due to reaction of only one Mn reagent state — most probably the first metastable state, a6DJ. This suggests a strong symmetry control in the entrance channel of the reaction, at least; that is, the Mn atom approaches along the C3 axis of SnCl4, so that the symmetry corresponding to the spatial configuration of the odd d electron is retained. In two cases, "blue" and "red," if not all, the luminescing MnCl* state seems to be produced on a surface that does not directly correlate with the reagents. As collision energy increases in each case, the reaction transition state seems to shift forward into the entrance valley, a result attributed to restricted access to the exit valley.

[1] We report the first ground-based passive microwave observations made from Troll station, Antarctica, which show enhanced mesospheric nitric oxide (NO) volume mixing ratio reaching levels of 1.2 ppmv, or 2–3 orders of magnitude above background, at 70–80 km during small, relatively isolated geomagnetic storms in 2008. The mesospheric NO peaked 2 days after enhanced NO at higher altitudes (110–150 km) measured by the SABER satellite, and 2 days after peaks in the >30 keV and >300 keV electron flux measured by POES, although the 300 keV electron flux remained high. High time resolution data shows that mesospheric NO was enhanced at night and decayed during the day and built up to high levels over a period of 3–4 days. The altitude profile of mesospheric NO suggests direct production by ∼300 keV electron precipitation. Simulations using the Sodankyla Ion and Neutral Chemistry model show that the delay between thermospheric and mesospheric NO enhancements was primarily a result of the weaker production rate at lower altitudes by ∼300 keV electrons competing against strong day-time losses.

Terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) are two novel techniques for the physical characterization of pharmaceutical drug materials and final solid dosage forms, utilizing spectral information in the far infrared region of the electromagnetic spectrum. This review focuses on the development and performance of pharmaceutical applications of terahertz technology compared with other tools for physical characterization. TPS can be used to characterize crystalline properties of drugs and excipients. Different polymorphic forms of a drug can be readily distinguished and quantified. Recent developments towards a better understanding of the fundamental theory behind spectroscopy in the far infrared have been discussed. Applications for TPI include the measurement of coating thickness and uniformity in coated pharmaceutical tablets, structural imaging and 3D chemical imaging of solid dosage forms.

The far-infrared properties of all five known polymorphic forms of the drug sulfathiazole have been studied by terahertz pulsed spectroscopy and low-frequency Raman spectroscopy. The observed spectra of the different polymorphs are distinctly different. Terahertz pulsed spectroscopy proves to be a rapid and complementary alternative to other physical characterization techniques reported in the literature for distinguishing between the five forms. Variable-temperature measurements (293-473 K) of all polymorphic forms have been performed. The phase transitions observed have been related to thermal analysis data. Form I is the form stable at high temperature of sulfathiazole with a melting point of about 475 K. Form II melts at around 470 K and recrystallizes at higher temperatures to form I. Forms III, IV, and V all convert to form I via a solid-solid phase transition at temperatures below 450 K. The phase transitions can be monitored by terahertz pulsed spectroscopy. Polymorphic impurities of the samples can be detected in the room temperature spectra and their effect on the phase transition behavior can be studied.

We report the use of a terahertz pulsed imaging technique for three-dimensional chemical mapping. Terahertz radiation reflected from a sample was measured pixel-by-pixel in time domain using a terahertz pulsed imaging system developed at TeraView Ltd, UK. The recorded terahertz waveforms were then transformed into frequency domain using time-partitioned Fourier transform. Structural maps of samples were obtained by analyzing the terahertz time-domain data whilst chemical maps were obtained from terahertz spectral data sets. For a sample comprising chemical A at the surface of a polyethylene pellet and chemical B buried inside the pellet, we have separated the component spatial patterns of the two chemicals using their spectral fingerprints. The reconstructed three-dimensional chemical maps not only locate the chemicals in the object, but also identify each chemical. We also demonstrate the capabilities of terahertz pulsed imaging for non-destructive analysis of coating thickness and quality, and for detecting and identifying explosive materials such as RDX.

Terahertz pulsed spectroscopy (TPS) is a new technique that is capable of eliciting rich information when investigating pharmaceutical materials. In solids, it probes long-range crystalline lattice vibrations and low energy torsion and hydrogen bonding vibrations. These properties make TPS potentially an ideal tool to investigate crystallinity and polymorphism. In this study four drugs with different solid-state properties were analyzed using TPS and levels of polymorphism and crystallinity were quantified. Carbamazepine and enalapril maleate polymorphs, amorphous, and crystalline indomethacin, and thermotropic liquid crystalline and crystalline fenoprofen calcium mixtures were quantified using partial least-squares analysis. Root-mean-squared errors of cross validation as low as 0.349% and limits of detection as low as approximately 1% were obtained, demonstrating that TPS is an analytical technique of potential in quantifying solid-state properties of pharmaceutical compounds.

Recent events have led to dramatic changes to the methods em ployed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new technologies that can be applied to security screening, either to simplify or speed up the checking process, or to provide additional functionality. Terahertz (THz) technology is a promising, emerging candidate. In previous publications we have shown how our THz pulsed imaging systems can be used to image threat items, and have demonstrated that explosive materials have characteristic THz spectra. 1 We have also demonstrated that non-metallic weaponry can be imaged when concealed beneath clothing. In this work we examine more closely the properties of barrier and potential confusion materials. We demonstrate that barrier materials have smooth spectra with relatively low attenuation. We further demonstrate that the terahertz spectra of several common chemicals and medicines are distinct from those of threat materials. Keywords : security screening, terahertz, applications, explos ive detection, people screening, imaging, spectroscopy 1. INTRODUCTION 1.1 Critical issues in security screening Recent events have demonstrated the need for ever more effective security screening, and for systems capable of detecting contraband. A wide variety of techniques are already available, for the detection of a variety of threats, such as weapons or explosives, or illicit items, ranging from drugs to illegal immigrants. Current methods of bag screening in the United States and elsewhere typically use X-ray inspection techniques with some use of further image analysis, manual search and chemical trace detection. Passenger screening relies heavily on archway and handheld metal detectors that are deployed throughout most airports. However, these techniques are not foolproof, and beneficial enhancements could be made in detecting the following : € Weapons containing a small amount of metal; € Ceramic weapons; € Explosive materials; € Chemical and biological threats. Emerging technologies, such as X-ray backscatter and millimeter wave imaging might be employed to address some current deficiencies. However, the routine use of ionising X-rays raises health concerns, whilst millimeter wave approaches have a limited spatial resolution. It is also unclear whether either technique can provide spectroscopic substance identification. Thus, X-ray and millimeter wave portals are likely to prompt frequent further searching whenever an image indicates a suspect item or area. False alarms can greatly increase the cost and reduce the throughput of screening systems; throughput is crucial in high-volume situations such as in major airports. A further factor is the high dependence of current techniques on human

Hitherto unobserved overtone and combination bands of nitrous acid have been investigated by Fourier-transform infrared absorption spectroscopy and through the resonance enhancements they provide in the two-photon excition spectrum for forming OH(X) photofragments. Analysis of the band profiles associated with the second and third O—H stretching overtones of trans-HONO, and of the energy disposal into the OH(X) fragments resulting from two-photon dissociation mediated by these overtone levels, provide some clues as to the mechanism for intramolecular vibrational energy redistribution (IVR) within these vibrationally excited molecules. The work serves to highlight further the extreme sensitivity of vibrationally mediated photodissociation (VMP) as a means of revealing weak O—H stretching overtones, even in situations (as here) where the species of interest is but a minor constituent of an equilibrium mixture.