A transboundary transport episode of nitrogen dioxide as observed from GOME and its impact in the Alpine region

[摘要] High tropospheric NO₂ amounts are occasionally detected by space-bornespectrometers above cloudy scenes. For monitoring of near-ground airpollution such data are not directly applicable because clouds shield thehighly polluted planetary boundary layer (PBL). We present a method based ontrajectories which implicitly estimates the additional sub-cloud NO₂distribution in order to model concentrations at ground stations. The methodis applied to a transboundary pollution transport episode which led to highNO₂ vertical tropospheric column densities (VTCs) over middle Europeobserved by the Global Ozone Monitoring Experiment (GOME) instrument aboveclouds on 17 February 2001. The case study shows that pollution originallyresiding near the ground in central Germany, the Ruhr area and adjacentparts of the Netherlands and Belgium has been advected to highertropospheric levels by a passing weather front. Combining the above-cloudNO₂ VTCs with trajectory information covering the GOME columns andincluding their sub-cloud part yields an estimate of the total NO₂ distribution within the tropospheric columns. The highly polluted air massesare then traced by forward trajectories starting from the GOME columns tomove further to the Alpine region and their impact there is assessed.Considering ground-based in-situ measurements in the Alpine region, weconclude that for this episode, at least 50% of the NO₂ concentration recorded at the sites can be attributed to transboundarytransport during the frontal passage. This study demonstrates the potentialof using NO₂ VTCs from GOME detected above clouds when combined withtransport modelling.

[学科分类] 大气科学