Megacities are a hotspot for higher greenhouse gas emissions that can have a devastating impact on the wider environment. An ongoing study called Cityzen is looking into the effect that air pollution has on the local, regional and global environment using satellite and on-site observations. Sixteen partners in eleven countries in Europe, Africa and Asia are involved in the project, which is headed by the Norwegian Meteorological Institute. Several sites around the world have already been chosen as places to carry out intensive case studies: the East Mediterranean, the Po Valley (Italy), the Benelux region and the Pearl River Delta (China). The project is also looking at the effects of climate change on air quality within megacities. The study has several linked objectives which aim to act as a scientific basis for air quality legislation and city planning in the future. By understanding air pollution around megacities, the partners hope to estimate the future impact of changes in emissions in relation to increasing urban populations. The project hopes to gain a better understanding of how megacities influence and are responding to climate change. By analysing the options available to them, the partners hope to diminish the effects of urban air pollution on human health. The partners want to harness the results and methodologies applied during the course of the project and put them into operational use. Furthermore, by assessing the results of the project the partners want to make suggestions to policy-makers on which mitigation options exist to reduce environmental problems associated with megacities. The project has already made a number of observations based on global satellite pictures of air pollutants. On-site measurements in the Pearl River Delta, London and Athens are ongoing with a new measurement network being set up in Turkey. The modelling of the impact megacities have on air pollution has already highlighted hotspots in the East east Mediterranean around Istanbul, Athens and Cairo, as well as the Pearl River Delta in China. The project has been successfully communicated to the wider public through a number of different platforms, including the project's own website, newspaper articles, conference lectures, various publications and an assessment of megacities being drawn up by the World Meteorological Organisation and the International Global Atmospheric Chemistry (IGAC) project.