The presence of a weekly cycle in the measured tropospheric NO2 VCD allows the identification of anthropogenic sources. In China, no weekly pattern can be found. Metropolitan areas with other religious and cultural backgrounds (Jerusalem, Mecca) show different weekly patterns corresponding to different days of rest. Sunday NO2 VCDs are about 25–50% lower than working day levels. In the cycles of the industrialized regions and cities in the US, Europe and Japan a clear Sunday minimum of tropospheric NO2 VCD can be seen. We demonstrate the statistical analysis of weekly cycles of tropospheric NO2 VCDs for different regions of the world. Applying sophisticated algorithms, vertical column densities (VCD) of tropospheric NO2 can be determined. The Global Ozone Monitoring Experiment (GOME) on board the ESA-satellite ERS-2 allows measurements of NO2 column densities. This "weekend effect" is well known from local, ground based measurements, but has never been analysed on a global scale before. Since human activity in industrialized countries largely follows an artificial seven-day cycle, fossil fuel combustion is expected to be reduced during weekends. 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 NOx. Nitrogen oxides (NO+NO2=NOx) are important trace gases in the troposphere with impact on human health, atmospheric chemistry and climate. The present study demonstrates that enhanced PCO of NO with photocatalyst nanofiber under solar light irradiation can be optimally realized. The activity of the nanofiber photocatalysts was improved by increasing the irradiation area and residence time and optimized at relative humidity of 50%.Conclusion % of Zn to the TiO2 photocatalyst, and this optimal amount of added dopant was in accord with the X-ray photoelectron spectroscopy measurement. The efficiency of PCO under irradiation from full spectrum of wave lengths was optimized by adding 0.10 wt. The TiO2/ZnO composite nanofiber photocatalyst has lower band-gap than TiO2 nanofibers, which favors photo-electron generation, because introduction of ZnO causes charge imbalance and formation of the unsaturated chemical bonds on the surface, increasing the catalyst surface oxygen vacancy and generation of the oxidation radicals, thereby increasing PCO. The nanopores formed between nano-crystallites of nanofibers were found to increase both adsorption and activity of the photocatalyst. There is a demand to develop nano-photocatalyst that has better performance as compared to existing TiO2 nanoparticles that are difficult to separate and reuse.ResultsBoth TiO2 and TiO2/ZnO composite nanofibers prepared using a sol–gel assisted electrospinning revealed higher photocatalytic oxidation (PCO) of NO than TiO2 nanoparticles of 100 nm.
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