This project tackled some of the key uncertainties that remain in urban air processes, including how polluting chemicals are transformed or oxidised in the atmosphere, how gases and particles interact, how pollution is dispersed by weather, how remote emissions from outside the city impacts on urban populations and how the presence of pollution itself may affect feedback and alter on meteorology in cities. The project focused its study on three key types of harmful air pollution: particulate matter (referred to as PM), nitrogen dioxide (NO2), and ozone O3. The project was a collaboration between ten UK Universities, three leading Chinese research institutes, all part of the Chinese Academy of Sciences, Peking University and three UK partner research organisations (CERC, NPL, Met Office). The project included two periods of intensive observations in the centre of Beijing, in the contrasting atmospheric conditions of winter and summer. The experiments made measurements at the surface, and in the vertical using a unique 1000ft meteorological tower. These experiments generated a complex and multiparameter dataset that can challenge state of the art computer models of urban pollution. By challenging models with detailed data, their capabilities can be assessed and their weaknesses and failings identified, and then targeted for improvement. The project used state of the art models from the UK and from China, and developed methods to generate very high spatial resolution estimates of pollution at the surface, a type of data that is essential when studying the health effects of pollution, or evaluating how successful a future policy might be.

Science objectives:
-Assess whether the processes by which pollutants are transformed or removed through chemical reactions and photolysis, and the rates of formation and conversion of particulate matter via atmospheric reactions, are consistent with our understanding obtained from studies in environments which differ fundamentally from that observed in Beijing.

-Quantify how the detailed properties of particulate matter evolve and can influence their physical properties and behaviour in the atmosphere (e.g. haze formation), and elucidate the mechanisms whereby those properties may interact and feedback on urban scale and regional meteorology. We address these overarching objectives through two field observation periods in Beijing contrasting winter and summer conditions, drawing together a wide range of instrumentation and modelling tools from both countries and using the unique IAP tall tower in the city centre.