Prediction of the downward flux of atmospheric radiation in a polluted urban environment

Measurements of hourly totals of atmospheric lung-wave emission (LI) made over a two-year period at sites in and near Christchurch. New Zealand, are used to evaluate the performance of several semi-theoretical estimation equations for LI. At both sites the estimation equations of Brutsaert, Brunt and Idso-Jackson all give similar systematic diurnal estimation errors, with general underestimation of atmospheric emissivity late evening and early morning and overestimation at other limes, although the underestimation is much greater and the general performance of the equations much poorer in the urban situation. The systematic estimation error appears to result from an inability to reconcile surface data input to the equations with a bulk atmospheric emission. However, in the urban situation, it seems that pollution emissivity coincident with early morning inversion conditions Is superimposed upon the model underestimation caused primarily by the inversion conditions. Accordingly, a method is described by which pollution emissivity can be derived from a 'grey body' emissivity approximation model utilising vertical soundings and incorporated into the predictive equations resulting in significant improvements to prediction of LI in central Christchurch.