A new experimental technique measures j(O3-O(1D)), the rate of solar photolysis of ozone to singlet oxygen atoms: O3+h&ngr;→O2+O(1D). A flow actinometer carries dilute O3 in N2O into direct sunlight where the O(1D) formed reacts with N2O to form NO which chemiluminescence detects, with a time resolution on the order of one minute. Measurements indicate a photolysis rate of 1.2 (¿.2) ¿10-5 s-1 for a cloudless sky, 45 ¿ zenith angle, 0.345 cm ozone column and zero albedo. Ground level results (elevation 1.8 km) compare with theoretical calculations based on the UV actinic flux as a function of ozone column and solar zenith angle.