Vertical atmospheric structure estimated by heat island intensity and temporal variations of methane concentrations in ambient air in an urban area in Japan

The vertical atmospheric structure was studied and evaluated based on the distribution and variation of the air temperature in an urban area in Japan. A difference was observed in the annual mean diurnal variation of the air temperature between the urban site and a suburban site. The maximum and minimum temperatures were 1.64∘C at 1:00 and 1.17∘C at 15:00, respectively, resulting in an estimated intrinsic heat island intensity of 0.47 (=1.64–1.17)∘C. The height of the temperature inversion layer was approximately 90 m above the ground, based on the intrinsic heat island intensity in an area where no vertical air temperature was available. The temporal variations of the methane concentrations in ambient air and the contribution of automobile emissions were estimated and well accounted for by the postulated temperature inversion layer.