Nitrogen-oxide layer over the urban heat island in Okayama City

NOx concentration above an urban area was measured using a newly developed lightweight air sampler suspended from a tethered balloon. A high concentration of NOx was detected at a level which coincided with the bottom of the elevated inversion layer, at a height of approximately 100 m above the ground. The maximum concentration at this point was twice that of measurements taken at ground level. While the reason for this phenomenon is not confirmed, several hypotheses are proposed.