Variations in short and long wave radiation were measured across the city of Christchurch over a five month period to mid-winter 1976. Two fixed climate stations were the basis of data collection, with mobile traverse s completing the spatial pattern of urban/ rural variations in radiation.

Analysis of this data showed an average attenuation of incoming short wave radiation for clear days of 14.9 % in the central city, with peaks as high as 30 %. A definite daily and seasonal trend was perceived with greater attenuation at lower solar elevations. These figures appear to be quite high compared with the attenuation reported from other mid-latitude cities. The atmospheric transmissivity for direct beam radiation was found to be dominantly influenced by smoke pollution, but continued attenuation in the summer months suggested the presence of pollutants not measured in this study.

Long wave radiation was also shown to have a definite urban/rural trend, with the urban excess being an average daily 8.5% for clear days which is comparable with the only other such study. The increase in long wave radiation nearly exactly balanced the short wave deficit in urban areas during daytime, but at night the urban area showed a gain in radiant energy from this source over the rural areas. Examination of possible reasons for the urban excess long wave radiation again indicated the importance of smoke pollution in radiation transfer, but the true influence of urban temperatures was thought to have been masked by an urban thermal lag found to coincide with peak incoming long wave radiation during the day.

Application of simple models to predict incoming short and long wave radiation achieved varied success, but also showed the importance of particulates in the transfer of short and long wave radiation. The use of models helped in the development of a hypothesis using the urban pollutant layer to explain the urban/rural divergence in both long and short wave radiation.