Vertical Profiles of Aerosol and Radiation and the Influence of a Temperature Inversion: Measurements and Radiative Transfer Calculations

Abstract

The results of an airborne experiment performed near Mönchengladbach (Germany) in November 1993 are reported. Besides meteorological data, vertical profiles of aerosol properties (number concentration, size distribution) and radiation (downwelling solar and UV irradiance, JNO₂ photolysis frequency) under cloudless conditions are presented, and the influence of a strong temperature inversion is studied. From the measured vertical profiles of the aerosol size distribution, single-scattering properties of the particles (volume scattering coefficient, asymmetry parameter, backscattering ratio) are calculated. On the basis of the aerosol and meteorological measurements, detailed radiative transfer calculations are performed in order to model vertical profiles of the downwelling UV irradiance and JNO₂ photolysis frequency. The data of the calculated UV irradiance mostly agree with the measured values within the range given by the measurement errors. Introducing moderate absorption into the model improves the agreement. For the JNO₂ photolysis frequency there are some differences. However, the strong influence of an enhanced number of optically efficient aerosol particles below a temperature inversion on downwelling radiation could be shown for the UV irradiance as well as for the JNO₂ photolysis frequency by the measurements and the calculations.