The use of ammonia as an actionometer for measurement of the solar flux in the region 1950-2150¿ is presented. The solar flux was found to be 2.7¿108 photons/cm2 s at ground level in this wavelength interval in an area with minimum overhead ozone concentration. The advantages of this method over previously used methods are discussed, and the results are related to the present estimates of the tropospheric photodissociation rates for the freons CFCl3 and CF2Cl2 by radiation in this wavelength region.