Passive remote sensing of nitrogen dioxide as a tool for tracking air pollution in urban areas: the Madrid urban plume, a case of study

This paper describes the experimental potential of a classic ground-based passive remote sensing technique, the dispersive correlation spectroscopy (DCS), for the study of non-industrial urban plumes. The text presents this technique as an alternative tool to study some aspects of air pollution in cities, in contrast to the information supplied by air pollution monitoring networks. The results obtained with DCS in the study of Madrid plume in winter, one of the most important cases of urban pollution taking place in southern Europe, are presented here as an example of the DCS application. This highly inhabited zone, where pollutant emissions have essentially an urban origin, stays frequently under the influence of high-pressure systems, which strongly condition the efficient ventilation of the area and produce air pollution episodes of certain importance. The study presented here has been based on the previous technical improvement of the commercial COSPEC V instrument and on its use as a passive remote sensor from a mobile laboratory measuring NO2 total column. The formation process of the Madrid plume, its horizontal limits and the dynamics of transport are some of the aspects documented with this technique.