Spatiotemporal Inhomogeneity in Nitrogen Dioxide (NO₂) over Fukuoka Observed by Car MAX-DOAS

Abstract

Nitrogen dioxide (NO₂) observations have been made using car Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) in Fukuoka, an urban area in Japan, to clarify the spatiotemporal inhomogeneity in NO₂. We developed instruments for Car MAX-DOAS, and NO₂ measurements were conducted on 15 August 2015 and 30 November 2015 on the Fukuoka Urban Expressway, along the closed circular route. For both days, in the morning, the maxima were observed around the city center (in the northeast part of the circular route), whereas in the afternoon, the maxima were observed in the south/southeast part of the circular route (to the south/southeast of the city center). Analysis of the surface wind field indicates that the NO₂ inhomogeneity is strongly related to the inhomogeneity of NO_x sources and to horizontal transport of high concentrations from the city center and low concentrations from the ocean via a land-sea breeze.