Review of empirical methods for the calculation of the diurnal NO2 photolysis rate coefficient

The rate coefficient for the photolysis of nitrogen dioxide (JNO2) is used in ambient photochemical air quality models as this photodissociation leads to the formation of tropospheric ozone. This review examines the effectiveness and efficiency of four methods for the calculation of JNO2. The nature of JNO2 is reviewed briefly with regard to temperature, pressure, zenith angle, altitude, albedo, clouds, atmospheric turbidity and atmospheric molecular absorption. Comparison of the four methods against a radiation transfer model, for three clear-sky days at different latitudes in Australia, shows that any of the methods may be used to approximate a clear-sky diurnal profile of JNO2, as the maximum variation between all models at noon was found to be 15%. However, more care needs to be taken when calculating other photolysis rate coefficients, such as JO3, as these are more susceptible to other variables such as the ozone column concentration. A simple procedure for calculating cloudy-day JNO2 is also illustrated.