D. J. Fish

University of Reading, Reading, England, United Kingdom

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Publications (19)34.86 Total impact

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    ABSTRACT: Using a flexible chemical box model with full heterogeneous chemistry, intercepts of chemically modified Langley plots have been computed for the 5 years of zenith-sky NO2 data from Faraday in Antarctica (65°S). By using these intercepts as the effective amount in the reference spectrum, drifts in zero of total vertical NO2 were much reduced. The error in zero of total NO2 is from one year to another. This error is small enough to determine trends in midsummer and any variability in denoxification between midwinters. The technique also suggests a more sensitive method for determining N2O5 from zenith-sky NO2 data.
    Journal of Quantitative Spectroscopy and Radiative Transfer 01/2001; · 2.38 Impact Factor
  • Journal of Quantitative Spectroscopy & Radiative Transfer - J QUANT SPECTROSC RADIAT. 01/2001; 68:337-349.
  • D. J Fish
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    ABSTRACT: An automatic hydrocarbon oxidation system that uses structure activity relationships to automatically calculate how aliphatic hydrocarbons breakdown in the atmosphere is described. The program includes functions to calculate average reaction rates and products for use in a reduced mechanism based on functional groups. Chemical concentrations from the reduced mechanism compare well with results from the regional atmospheric chemistry mechanism, RACM, for clean and polluted boundary layer scenarios. The main advantage of this approach is the ease of generating different reduced mechanisms for different emissions scenarios, such as for different countries, or to take account of reductions in the emissions of particular VOCs.
    Atmospheric Environment 01/2000; 34(10):1563-1574. · 3.11 Impact Factor
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    ABSTRACT: A recently published analysis of slant columns of NO2 observed at twilight at 45°S has identified trends of about 5%/decade between 1980 and 1998. This is twice the trend in tropospheric N2O, which is the source of stratospheric NO2. By means of a column photochemical model, we explore the sensitivity of NO2 to the observed trends in stratospheric temperature, O3 and H2O. The resulting calculated trends in NO2 are smaller than observed, and we cannot force agreement by varying the ozone or temperature trends. The calculated sensitivity of NO2 to stratospheric aerosol is large, and a 20% per decade decrease in aerosol surface area creates agreement. We conclude that a small residual in the statistical fit of aerosol to the NO2 measurements may remain, and is a likely cause of the trends found in the NO2 measurements.
    Geophysical Research Letters - GEOPHYS RES LETT. 01/2000; 27:3313-3316.
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    ABSTRACT: Recent urban measurements suggest that NO3 concentrations vary significantly with altitude in the lowest few hundred metres of the atmosphere. Calculations using a one-dimensional boundary layer model show that NO3 concentrations are small near the ground and increase with altitude to a maximum near the top of the nocturnal boundary layer (NBL). These results show that the NBL is not well mixed, and that where there are surface sources and sinks two-box models of the NBL are inadequate, and surface measurements are not representative and may lead to an underestimate of the oxidising capacity of the atmosphere.
    Atmospheric Environment 02/1999; 33(5):687-691. · 3.11 Impact Factor
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    ABSTRACT: A new method for retrieving the vertical profile of NO2 from ground-based measurements is applied to four months of measurements made at Aberdeen (57N) during part of SESAME from November 1994 to April 1995. The retrieval method is shown to be an invaluable tool both for deriving the true NO2 vertical column and for removing the tropospheric contribution to the vertical column. This dramatically reduces the effects of tropospheric pollution in the observations and enables a more appropriate comparison with stratospheric 3-D model results. The comparison confirms the accuracy of the model's transport and its reactive nitrogen photochemistry, although there are some detailed discrepancies.
    Journal of Atmospheric Chemistry 04/1998; 30(1):163-172. · 1.33 Impact Factor
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    ABSTRACT: A novel automated ground-based star-pointing spectrometer system has been constructed for long-term deployment in Antarctica. Similar to our earlier stellar system, a two-dimensional detector array measures the spectra of the star and the adjacent sky, so that auroral emission from the sky can be subtracted from the stellar signal. Some new features are an altitude -azimuth pointing mirror, so that the spectrometer does not move; slip rings to provide its power thereby avoiding flexing of cables and restriction of all-around viewing; and a glazed enclosure around the mirror to ensure protection from rain and snow, made from flat plates to avoid changing the focal length of the telescope. The optical system can also view sunlight scattered from the zenith sky. The system automatically points and tracks selected stars and switches to other views on command. The system is now installed at Halley in Antarctica, and some preliminary measurements of ozone from Antarctica are shown.
    Applied Optics 09/1997; 36(24):6069-75. · 1.69 Impact Factor
  • S. R. Aliwell, R. L. Jones, D. J. Fish
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    ABSTRACT: Zenith-sky observations of the seasonal evolution of BrO slant columns above Aberdeen (57°N) between November 1994 and April 1995 are presented. The measurements show maximum differential BrO slant columns (90°-81°) of 2.4×1014moleculescm-2 in January, decreasing to 1×1014 in spring. On a seasonal timescale, BrO slant columns are anticorrelated with NO2 slant columns, which is qualitatively consistent with BrONO2 being the main night-time bromine reservoir. There is some evidence for a small (5×1013moleculescm-2) increase in sunrise BrO slant columns inside the polar vortex, following chlorine activation on PSCs, as shown by measurements of large OClO slant columns.
    Geophysical Research Letters 01/1997; 24:1195-1198. · 3.98 Impact Factor
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    ABSTRACT: An intercomparison of zenith-sky UV-visible spectrometers was held at Camborne, UK, for 2 weeks in September 1994. Eleven instruments participated, from nine different European institutes which were involved with the Second European Stratospheric Arctic and Mid-latitude Experiment (SESAME) campaign. Four instruments were of the Systeme d'Analyse d'Observations Z6nithales (SAOZ) type, while the rest were particular to the institutes involved. The results showed that the SAOZ instruments were consistent to within 3% (10 DU) for ozone and 5% for NO 2. For ozone the results from these instruments agreed well with total ozone measurements by Dobson and Brewer spectrophotometers and integrated ozonesondes when the air mass factors for the SAOZ were calculated using the ozonesonde profiles. Differences of up to 10% in ozone and 30% in NO 2 were found between different instruments. In some cases these differences are attributable to the different absorption cross sections used in the analysis of the spectra, but other discrepancies remain to be investigated. A prominent source of error identified in the campaign was uncertainty in the derivation of the amount of absorber in the reference spectrum, which can contribute an error of up to 3% (10 DU) in ozone and 1.5 x 10 TM molecules cm -2 in NO 2.
    Journal of Geophysical Research 01/1997; 102(20):1411-1422. · 3.17 Impact Factor
  • D. J. Fish, S. R. Aliwell, R. L. Jones
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    ABSTRACT: A 1-D photochemical model, initialised with output from a chemical transport model and coupled to a radiative transfer model, is used to calculate BrO slant columns. Calculated BrO slant columns are shown to be in good agreement with measured values, which supports our current understanding of stratospheric bromine chemistry at middle latitudes, and argues against the need to invoke new chemistry or a new photolabile night-time bromine reservoir. The model calculations show that the seasonal variation of BrO slant columns results from seasonal variations in NO2 abundances. The occurrence of BrONO2 hydrolysis on sulphate aerosols is found to affect twilight BrO abundances, but no other heterogeneous reactions involving bromine species are important under the range of stratospheric conditions sampled. The zenith-sky measurements from Aberdeen in the winter of 1994-5 can be explained with present photochemical schemes and current estimates of approximately 20 pptv for the bromine content of the stratosphere.
    Geophysical Research Letters - GEOPHYS RES LETT. 01/1997; 24:1199-1202.
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    ABSTRACT: Summertime measurements of NO2 vertical column amounts over a 5 year period from May 1990 until February 1995 from Faraday Base, Antarctica, show a marked reduction following the arrival of the Mount Pinatubo volcanic aerosol in December 1991. Model calculations show that this reduction can be explained by BrONO 2 and N20 s hydrolysis on the volcanically enhanced aerosol, with the former dominating. Given the measurement and model uncertainties and lack of any treatment the effects of the quasi-biennial oscillation, the reduction in NO 2 is consistent with a BrONO 2 sticking coefficient gamma of 0.4. However, the best agreement between the model and the measurements occurs using a gamma of 0.2. Over the time span of the measurements the known increases in chlorine and bromine loadings have an effect of less than 2% on midsummer NO,_ columns. With background aerosols, summertime ozone catalytic losses are dominated by the HOx cycle between 12 and 18 km and by the NOx cycle at greater altitudes. With heavy aerosol loading, HOis the primary loss cycle from 12 to 22 km. The total ozone loss increases by 38% at 16 km as a result of heavy aerosol loading.
    Journal of Geophysical Research 01/1997; 102:12987-12993. · 3.17 Impact Factor
  • H K Roscoe, D J Fish, R L Jones
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    ABSTRACT: UV-visible measurements of stratospheric constituents require the ratio of a pair of spectra to be determined. If their wavelength calibrations differ and if an array detector is used, at least one spectrum must be interpolated. This introduces error if the spectrum is undersampled; the error is smaller if wavelength stability is good. Increasing the sampling ratio by making the spectral resolution poorer reduces the optical depths of absorption by constituents. Exact values of interpolation errors from real spectra are a difficult topic, but with a theoretical study with a simulated spectrum we show that the sampling ratio should exceed ~4.5 pixels/FWHM but need not exceed 6.5 pixels/FWHM. To avoid significant reduction in the optical depth of NO(2), the resolution should be smaller than ~1.0 nm FWHM. Hence a spectrometer system that measures both OClO and NO(3) by observing one order from one stationary grating should have more than ~1500 pixels, more than many currently available array detectors.
    Applied Optics 01/1996; 35(3):427-32. · 1.69 Impact Factor
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    ABSTRACT: Calculations of air-mass factors (AMFs) for ground-based zenith-sky UV-visible spectrometers are now well developed in laboratories where stratospheric constituents are measured with this technique. An intercomparison between results from the different radiative transfer models used to calculate AMFs at twilight is presented here. The comparison was made for ozone AMFs at 510 nm and for NO2 AMFs at 440 nm. Vertical profiles were specified. Results are presented firstly for calculations in a pure Rayleigh atmosphere, then including background aerosols. Relative differences between calculated AMFs from different models cause relative errors in vertical columns of ozone and NO2 measured by zenith-sky spectrometers. For commonly used averages over solar zenith angles, these relative errors are ±2.3% in the vertical column of ozone and ±1.1% in the vertical column of NO2. Refinements to the calculations, suggested by the intercomparison, should reduce these errors to ±1.0% for ozone and ±0.5% for NO2.
    Geophysical Research Letters 01/1995; 22(9):1113-1116. · 3.98 Impact Factor
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    ABSTRACT: Calculations of air-mass factors (AMFs) for ground-based zenith-sky UV-visible spectrometers are presented and discussed. Causes and size of errors in AMFs of ozone in the visible are evaluated. Errors can be caused by approximations in the calculation (intensity-weight approximation, ignoring the finite field of view of the instrument); by approximation in the scheme of the calculation (single scattering, ignoring refraction); or by variable geophysical parameters (vertical profile of constituents). These relative errors in AMF cause identical relative errors in vertical columns of ozone deduced from measurements by zenith-sky spectrometers. The mean of the relative errors of ozone AMFs due to using one set of AMFs for all seasons and locations is ±2.4% when averaged over the commonly used range of solar zenith angles.
    Journal of Quantitative Spectroscopy and Radiative Transfer 01/1995; 54:471-480. · 2.38 Impact Factor
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    D. J. Fish, R. L. Jones, E. K. Strong
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    ABSTRACT: The diurnal variation of BrO through sunrise and sunset has been measured above Cambridge, England, (52°N) during March and April 1994 using zenith sky spectroscopy. The measured BrO slant column at 90° solar zenith angle (SZA), relative to that at 80° SZA, is typically 1.5×1014 cm-2 but varies significantly from day to day. The average variation of BrO slant column with SZA through sunrise and sunset is in good agreement with predictions from a photochemical model, coupled to a radiative transfer model. The zenith sky measurements are consistent with in situ measurements of BrO concentrations and indicate that the inorganic bromine content of the stratosphere is 18-24 parts per trillion by volume (pptv).
    Journal of Geophysical Research 01/1995; 1001:18863-18872. · 3.17 Impact Factor
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    ABSTRACT: A new UV-visible spectrometer system that measures the absorption of light from stars and planets by constituents in the Earth's atmosphere is described. Because it can be used to make measurements at night, the system has a significant advantage for measuring polar constituents in winter, when conditions that might give rise to ozone loss are initiated. Other advantages arise from the use of a cooled two-dimensional CCD array as the detector: an array detector avoids spectral noise resulting from scintillation of stars or from clouds passing overhead and allows for the possibility of measuring several constituents simultaneously; its second dimension permits auroral light from the atmosphere adjacent to the star to be measured simultaneously and subtracted from the stellar light, and a modern low-noise CCD allows us to use a telescope of modest diameter. The few previous measurements of constituents made by the use of stellar absorption did not have these advantages. The instrument was configured for simplicity and ease of use in field measurements and was deployed outside in winter in Northern Sweden in 1991. Examples of ozone measurements are shown.
    Applied Optics 10/1994; 33(30):7126-31. · 1.69 Impact Factor
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    ABSTRACT: Measurements of stratospheric composition have been made with a novel star-pointing spectrometer. The instrument consists of a telescope that focuses light from stars, planets, or the moon onto a spectrometer and two dimensional CCD array detector. Atmospheric absorptions can be measured, from which atmospheric columns of several gases can be determined. The instrument was deployed in Abisko, 69 deg N, during the European Arctic Stratospheric Ozone Experiment (EASOE). The instrument has the potential for measuring O3, OClO, NO2, and NO3. In this paper, a method for the retrieval of vertical columns is described, and some examples of ozone measurements given.
    04/1994;
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    ABSTRACT: Total ozone was measured from Abisko, Sweden (68.4°N, 18.8°E) from January to early March 1992, by a new instrument which uses stars and the Moon as sources of UV-visible light for absorption spectroscopy. In addition, some zenith-sky observations were made. Ozone measurements obtained using both techniques are presented and compared with those from other instruments. Good agreement with simultaneous ozonesonde measurements is observed, but the stellar measurements appear systematically higher than total ozone measured by both SAOZ and TOMS.
    Geophysical Research Letters - GEOPHYS RES LETT. 01/1994; 21(13):1387-1390.
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    ABSTRACT: Significant ozone loss due to reactive chlorine from man-made chemicals has occurred near the poles in the last decade. In this paper, we describe a novel star-pointing UV-visible spectrometer to measure amounts of some reactive gases in the ozone layer and discuss its advantages. The instrument has the capability of measuring stratospheric amounts of O3, NO2, NO3 and OClO at night. By using the most modern cooled array detectors, good signal-to-noise ratios can be obtained with a modest telescope and a short integration time. By using a two-dimensional array, light from the atmosphere adjacent to the star is measured simultaneously and subtracted from the stellar light. As with measurements using the sun as a source of light, before spectral analysis the observed spectrum at low elevation must be divided by the spectrum of the same star measured at higher elevation. This removes absorption features due to gases in the atmosphere of the star itself. The amount of absorbing constituent in the earth's atmosphere is proportional to the ratio of the slant path to the vertical path through the atmosphere. This air-mass factor is maximized, and the random error in the measurement minimized, at elevation angles close to the horizon. The instrument was deployed at Abisko in Northern Sweden during the 1991/92 European Arctic Stratospheric Ozone Expedition. Despite unusually cloudy conditions, many spectra were recorded.
    Proc SPIE 02/1993;