Abstract
The role of clouds in photodissociation is examined by both modelling and observations. It is emphasized that the photodissociation rate is proportional to the actinic flux rather than to the irradiance. The actinic flux concerns the energy that is incident on a molecule, irrespective of the direction of incidence. The irradiance concerns the energy that is incident on a plane.
As far as the modelling aspect is concerned, a multi-layer delta-Eddington model is used to calculate irradiances, actinic fluxes, and photodissociation rates of nitrogen dioxide J(NO2) as a function of height in inhomogeneous atmospheres. For the considered wavelength interval [290–420 nm], Rayleigh scattering, ozone absorption, and Mie scattering and absorption by cloud drops and aerosols should be taken into account.
Further, a three-layer model is used to calculate the actinic flux above and below a cloud, relative to the incident flux, in terms of cloud albedo, zenith angle, and the albedo of the underlying and overlying atmosphere. Cloud albedo is mainly determined by cloud optical thickness. An expression for the incloud actinic flux is given as a function of in-cloud optical thickness. The three-layer model seems to be a useful model for the estimation of photodissociation rates in dispersion models.
It is stressed that both models in their present form cannot handle partial cloudiness.
It is shown that if no clouds are present, the actinic flux depends primarily on solar zenith angle. Further, the incident flux at the top of the atmosphere diminishes downward into the atmosphere due to the increasing effect of scattering. Therefore, the actinic flux usually increases with height, although above clouds the actinic flux sometimes decreases with height due to a large contribution of the upward scattered light.
For cloudy atmospheres, another important parameter with respect to the actinic flux is added: cloud optical thickness. Cloud optical thickness determines cloud albedo. It can be shown that incloud characteristics and cloud height are less important while describing the effect of a cloud on the actinic flux (outside the cloud). The in-cloud values of the actinic flux can exceed the values outside the cloud.
Finally, using the photostationary state relationship, a comparison is performed between model results and ground-based measurements as well as in-cloud air craft measurements.
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References
Bahe, F. C., Schurath, U., and Becker, K. H., 1980, The frequency of NO2 photolysis at ground level, as recorded by a continuous actinometer,Atmos. Environ. 14, 711–718.
Briegleb, B. P., 1992, Delta-Eddington approximation for solar radiation in the NCAR Community Climate Model,J. Geophys. Res. 97, 7603–7612.
Deirmendjian, D., 1969,Electromagnetic Scattering on Spherical Polydispersions, Elsevier, New York.
Demerjian, K. L., Schere, K. L., and Peterson, J. T., 1980, Theoretical estimates of actinic (spherically integrated) flux and photolysis rate constants of atmospheric species in the lower troposphere,Adv. Environ. Sci. Technol. 10, 369–459.
DeMore, W. B., Molina, M. J., Spander, S. P., Golden, D. M., Hampson, R. F., Kurylo, M. J., Howard, C. J., and Ravishankara, A. R., 1987, Chemical kinetics and photochemical data for use in stratospheric modeling, Evaluation No. 8 JPL Publication 87–41. NASA Jet Propulsion Lab., Pasadena.
Dickerson, R. R., Stedman, D. H., and Delany, A. C., 1982, Direct measurements of ozone and nitrogen dioxide photolysis rates in the troposphere,J. Geophys. Res. 87, 4933–4946.
Drummond, A. J. and Thekaerara, M. P., 1973,The Extraterrestrial Solar Spectrum, Institute of Environmental Sciences, Mount Prospect, Illinois.
Edlen, B., 1953, The dispersion of standard air,J. Opt. Soc. Amer. 43, 339–344.
Elskamp, H. J., 1989, National Air Quality Monitoring Network technical description, RIVM Report No. 228702017, RIVM, Bilthoven, The Netherlands.
Finlayson-Pitts, B. J. and Pitts, J. N., Jr., 1986:Atmospheric Chemistry: Fundamentals and Experimental Techniques, Wiley-Interscience, New-York, chap. 3, pp. 93–206.
Hale, G. M. and Querry, M. R., 1973, Optical constants of water in 200 nm to 200 µm wavelength region,Appl. Opt. 12, 555–563.
Hansen, J. E. and Travis, L. D., 1974, Light scattering in planetary atmospheres,Space Sci. Rev. 16, 527–610.
Joseph, J. H., Wiscombe, W. J., and Weinman, J. A., 1976, The delta-Eddington approximation for radiative flux transfer,J. Atmos. Sci. 33, 2452–2459.
King, M. D. and Harshvardhan, 1986, Comparative accuracy of selected multiple scattering approximations,J. Atmos. Sci. 43, 784–801.
Lacis, A. A. and Hansen, J. E., 1974, A parameterization for the absorption of solar radiation in the Earth's atmosphere,J. Atmos. Sci. 31, 118–133.
Madronich, S., 1987, Photodissociation in the Atmosphere: 1. Actinic flux and the effects of ground reflections and clouds,J. Geophys. Res. 92, 9740–9752.
Madronich, S. and Weller, G., 1990, Numerical integration errors in calculated tropospheric photodissociation rate coefficients,J. Atmos. Chem. 10, 289–300.
Nicholls, S. and Leighton, J., 1986, An observational study of the structure of stratiform cloud sheets: Part 1. Structure,Quart. J. R. Meteorol. Soc. 112, 431–460.
Parrish, D. D., Murphy, P. C., Albritton, D. L., and Fehsenfeld, F. C., 1983, The measurement of the photodissociation rate of NO2 in the atmosphere,Atmos. Environ. 17, 1365–1379.
Paltridge, G. W. and Platt, C. M. R., 1976, Radiometric processes in meteorology and climatology, inDevelopments in Atmospheric Sciences, vol. 5, Elsevier, New York, pp. 119–120.
Press, W. H., Flannery, B. P., Teukolsky, S. A., and Vetterling, W. T., 1986,Numerical Recipies, Cambridge Univ. Press, Cambridge, chap. 2, pp. 40–41.
Shettle, E. P. and Weinman, J. A., 1970, The transfer of solar irradiance through inhomogeneous atmospheres evaluated by Eddington's approximation,J. Atmos. Sci. 27, 1048–1055.
Slingo, A. and Schrecker, H.M., 1982, On the short-wave radiative properties of stratiform water clouds,Quart. J. R. Meteorol. Soc. 108, 407–426.
Spinhirne, J. D. and Green, A. E. S., 1978, Calculation of the relative influence of cloud layers on the received ultraviolet and integrated solar radiation,Atmos. Environ. 12, 2449–2454.
Stephens, G. L., 1978, Radiative properties of extended water clouds, Part II,J. Atmos. Sci. 35, 2123–2132.
Thompson, A. M., 1984, The effect of clouds on photolysis rates and ozone formation in the unpolluted troposphere,J. Geophys. Res. 89, 1341–1349.
Van Broekhuizen, H. J. and Van Kuijk, A., 1990, The chemical composition of cloud and rain water, 1st measuring campaign, 15 September 1989, GEOSENS bv, PO Box 12067, 3004 GB Rotterdam, The Netherlands (in Dutch).
Van de Hulst, H. C., 1974, The spherical albedo of a planet covered with a homogeneous cloud layer,Astron. Astrophys. 35, 209–214.
Van de Hust, 1981,Light Scattering by Small Particles, Dover Publ., New York.
Vila-Guerau de Arellano, J., Duynkerke, P. G., Jonker, P. J., and Builtjes, P. J. H., 1993, An observational study on subgrid effects for chemical species due to time and space averaging,Atmos. Environ. 27A 353–362.
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van Weele, M., Duynkerke, P.G. Effect of clouds on the photodissociation of NO2: Observations and modelling. J Atmos Chem 16, 231–255 (1993). https://doi.org/10.1007/BF00696898
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DOI: https://doi.org/10.1007/BF00696898