ModellingNO conversion by using probability density functions

An expression for concentration fluctuations in a smoke plume is derived from airborne measurements ofNO _X. A linear relation between the standard deviation of the fluctuations around a Gaussian concentration profile and the average gradient in the concentrations is assumed. With this relation the probability density function of expectedNO ₂ concentrations at 3 km from a source ofNO _X is modelled under the assumption of photostatic equilibrium, and is compared with measurements. A parametrisation for the concentration fluctuations of std(C)= 26(+/–7)*dc/dr is proposed (r in metres). CalculatedNO ₂ distributions are in reasonable agreement with the measurements and the averageNO ₂ concentration appeared not to be affected by the concentration fluctuations in theNO _X concentration. The spatial resolution of all measurements was 40 m.