Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 3 4 2003 10.5194/acpd-3-3451-2003 http://www.atmos-chem-phys-discuss.net/3/3451/2003/ http://www.atmos-chem-phys-discuss.net/3/3451/2003/acpd-3-3451-2003.html http://www.atmos-chem-phys-discuss.net/3/3451/2003/acpd-3-3451-2003.pdf 3451 3467 2003-07-03 Weekly cycle of NO<sub>2</sub> by GOME measurements: A signature of anthropogenic sources S. Beirle U. Platt M. Wenig T. Wagner Institut für Umweltphysik, Universität Heidelberg, Germany NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Nitrogen oxides (NO+NO<sub>2</sub>=NO<sub>x</sub>) are important trace gases in the troposphere with impact on human health, atmospheric chemistry and climate. Besides natural sources (lightning, soil emissions) and biomass burning, fossil fuel combustion is estimated to be responsible for about 50\% of the total production of&nbsp; NO<sub>x</sub>. Since human activity in industrialized countries largely follows an artificial seven-day cycle, fossil fuel combustion is expected to&nbsp; be reduced during weekends. This "weekend effect" is well known from local, ground based measurements, but has never been analysed on a global scale before.<br> <br> The Global Ozone Monitoring Experiment (GOME) on board the ESA-satellite ERS-2 allows measurements of&nbsp; NO<sub>2</sub> column densities. Applying sophisticated algorithms, vertical column densities (VCD) of tropospheric NO<sub>2</sub> can be determined. We demonstrate the statistical analysis of weekly cycles of tropospheric NO<sub>2</sub> VCDs for different regions of the world. In the cycles of the industrialized regions and cities in the US, Europe and Japan a clear Sunday minimum of tropospheric NO<sub>2</sub> VCD can be seen. Sunday NO<sub>2</sub> VCDs are about 25&ndash;50% lower than working day levels. Metropolitan areas with other religious and cultural backgrounds (Jerusalem, Mecca) show different weekly patterns corresponding to different days of rest. In China, no weekly pattern can be found.<br> <br> The presence of a weekly cycle in the measured tropospheric NO<sub>2</sub> VCD allows the identification of anthropogenic sources. In addition, the fraction of emissions subjected to a weekly cycle (mainly transport, power generation) with respect to a constant background (all kind of natural sources, biomass burning, heavy industry) can be estimated. Furthermore, we estimated the lifetime of tropospheric NO<sub>2</sub> by analysing the mean weekly cycle over Germany in detail, obtaining a value of about 12 h.