Measurement of the photodissociation coefficient of NO2 in the atmosphere: I. Method and surface measurements

An instrument, specifically designed for measurements from a balloon platform in the stratosphere, has been used to obtain ground-level values of the atmospheric photodissociation coefficient of nitrogen dioxide, J _{NO 2}.A typical clear-sky value is 8.0×10^-3 s^-1 when the solar zenith angle is 40°. Measurements were made as a function of solar zenith angle and correlated with a calibrated Eppley UV radiometer. It is shown that J _{NO 2}may be expressed as a simple function of the radiometer output so that estimates of J _{NO 2}can be made using just an upward looking radiometer to an accuracy of about 20%. The measurements are also found to be in good agreement with calculations of J _{NO 2}using a simplified isotropic multiple scattering computer routine.