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Free Content Boundary layer photochemistry during a total solar eclipse

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Simultaneous measurements of radiation, photolysis frequencies, O3, CO, OH, PAN and NO x species were carried out in the boundary layer, along with pertinent meteorological parameters, under total solar eclipse conditions. This experiment performed at about 34 solar zenith angle and noontime conditions thus provided a case study about the interactions between radiation and photochemistry under fast ''day-night'' and ''night-day'' transitions, at high solar elevation. The results reveal a close correlation of photolysis frequencies jO(1D) and jNO2with the UV radiation flux. All three parameters show, due to the decreasing fraction of direct radiation at shorter wavelengths, much weaker cloud shading effects than global solar radiation. NO and OH concentrations decrease to essentially zero during totality. Subsequently, NO and OH concentrations increased almost symmetrically to their decrease preceding totality. The NO/NO2 ratio was proportional to jNO2over 30 min before and after totality indicating that the partitioning of NO x species is determined by jNO2. Simple box model simulations show the effect of reduced solar radiation on the photochemical production of O3 and PAN.

Wa¨hrend der totalen Sonnenfinsternis am 11. August 1999 wurden simultane und kontinuierliche Messungen von O3, CO, OH, PAN and NO x , Strahlung, Photolysefrequenzen und relevanten meteorologischen Parametern durchgefu¨hrt. Dieses Experiment, durchgefu¨hrt etwa am Mittag, bei 34 Zenithwinkel der Sonne, ermo¨glichte die Untersuchung der Interaktion von Strahlung und Photochemie fu¨r schnelle Tag-Nacht und Nacht-Tag-U¨berga¨nge bei hohem Sonnenstand. Die Ergebnisse zeigen eine enge Korrelation der Photolysefrequenzen jO(1D) und jNO2 mit dem UV-Strahlungsfluss. Alle drei Parameter zeigen, wegen des abnehmenden Anteils direkter Sonnenstrahlung bei kurzen Wellenla¨ngen, erheblich geringere Abschwa¨chung durch Wolken als die Globalstrahlung. NO und OH gehen wa¨hrend der Verdunkelungsphase auf Null herunter. Danach steigen NO und OH nahezu symmetrisch zum vorherigen Abfall wieder an. Das NO/NO2-Verha¨ltnis war 30 min vor bis 30 min nach der Totalita¨t proportional zu jNO2 und zeigte damit, dass die Partitionierung von NO x durch jNO2 bestimmt wurde. Mit einem einfachen Boxmodell wurde der Effekt der reduzierten Sonnenstrahlung auf die photochemische Produktion von O3 und PAN berechnet.

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Document Type: Research Article

Publication date: May 1, 2001

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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