Hydroxyl radical and ozone measurements in England during the solar eclipse of 11 August 1999

The solar eclipse on 11 August 1999 provided a rare opportunity to observe the remarkably dynamic character of atmospheric photochemistry. OH formation is driven by sunlight, and the rapid changes in light intensity associated with a solar eclipse provide a unique, yet natural perturbation experiment to study the response of OH and the ensuing chemistry. Highly time‐resolved measurements of OH and its rate of primary production were made at ground level during a 97% solar eclipse at Silwood Park, Ascot (51°25′N, 0°41′W) on 11 August 1999. The solar ultraviolet flux fell almost to nighttime levels, and the OH concentration decreased dramatically to below the detection limit of the instrument (2.1×105 molecule cm−3), before increasing again. The OH concentration is well correlated (r=0.88) to its rate of primary production from ozone photolysis. Shortly after maximum eclipse the concentration of ozone fell to 60% of its value at first contact. The study provides a striking demonstration of the dynamics of photochemical processes in the planetary boundary layer.

[1]  James Lee,et al.  Absorption cross‐section measurements of water vapour and oxygen at 185 nm. Implications for the calibration of field instruments to measure OH, HO2 and RO2 radicals , 2000 .

[2]  Michael J. Pilling,et al.  Modeling OH, HO2, and RO2 radicals in the marine boundary layer: 1. Model construction and comparison with field measurements , 1999 .

[3]  A master equation study of laser‐generated interference in the detection of hydroxyl radicals using laser‐induced fluorescence , 1998 .

[4]  B. J. Whitaker,et al.  Fast photomultiplier tube gating system for photon counting applications , 1998 .

[5]  M. Kawasaki,et al.  Photochemistry of Ozone: Surprises and Recent Lessons , 1998, Science.

[6]  D. Chakrabarty,et al.  Fluctuation in ozone column over Ahmedabad during the solar eclipse of 24 October 1995 , 1997 .

[7]  Michael J. Pilling,et al.  Implementation and initial deployment of a fieldinstrument for measurement of OH and HO2 in thetroposphere by laser-induced fluorescence , 1997 .

[8]  Martin Hessling,et al.  In situ measurement of tropospheric OH radicals by laser-induced fluorescence - a description of the KFA instrument , 1995 .

[9]  The Measurement of OH and HO2 in the Atmosphere , 1995 .

[10]  H. Dorn,et al.  A New In Situ Laser Long-Path Absorption Instrument for the Measurement of Tropospheric OH Radicals , 1995 .

[11]  William H. Brune,et al.  Measurement of tropospheric OH and HO2 by laser‐induced fluorescence at low pressure , 1994 .

[12]  OH multipass absorption: Absolute and in situ method for local monitoring of tropospheric hydroxyl radicals , 1994 .

[13]  F. Mims,et al.  Fluctuations in column ozone during the total solar eclipse of July 11, 1991 , 1993 .

[14]  G. Mount.  The measurement of tropospheric OH by long path absorption 1. Instrumentation , 1992 .

[15]  D. Tanner,et al.  Ion-assisted tropospheric OH measurements , 1991 .

[16]  C. Y. Chan,et al.  Third-generation FAGE instrument for tropospheric hydroxyl radical measurement , 1990 .

[17]  C. R. Burnett,et al.  Atmospheric hydroxyl response to the partial solar eclipse of May 30, 1984 , 1985 .

[18]  U. Platt,et al.  Groundlevel OH radical concentration: New measurements by optical absorption , 1984 .

[19]  V. Agashe,et al.  Changes in the concentration of mesospheric ozone during the total solar eclipse , 1982 .

[20]  D. H. Stedman,et al.  Variations in the ambient ozone concentration during the 26 February 1979 solar eclipse , 1980 .

[21]  H. Levy.  Photochemistry of the lower troposphere , 1972 .

[22]  H. Niki,et al.  Carbon Monoxide Balance in Nature , 1972, Science.