Aerosol sources, processes and effects on the urban boundary layer: highlights from the Air Pollution and Human health programme

Globally, air quality in megacities such as Beijing is of increasing interest due to its impact upon health. The Air Pollution and Human Health Beijing (APHH-Beijing) project is a joint UK-China collaboration which aims to identify both the concentrations and sources of urban pollution in Beijing and people's exposure to this pollution in order to further understand its impact upon health. A major component of this project was a detailed characterisation of aerosol sources and composition during two intensive measurement periods at the Institute of Atmospheric Physics in north central Beijing in the winter of 2016 and the summer of 2017 both including several high pollution episodes. This paper will provide an overview of the aerosol measurements and will present new measurements of the black carbon fluxes by eddy correlation - the first measurements of this type in an urban environment. The mixing state of black carbon was examined using a single particle soot photometer sampling downstream of a mass size selector (CPMA) and this was used to examine different sources of black carbon and their mixing state. The composition of PM1 was measured using an AMS and this was used to establish the source apportionment of organic matter using positive matrix factorization. There is significant evidence for oxidised organic matter in wintertime and secondary organic matter is dominant in summer. A Time of Flight Chemical Ionization Mass Spectrometer coupled with an inline filter inlet (FIGAERO) was used to obtain molecular information of the semi-volatile organic matter and its partitioning between the gas and particle phase. This was to probe the relative contributions of different sources and processes to the pollution in Beijing and how these source profiles vary temporally during the campaigns including those relating to biomass burning, vehicular emissions and secondary processes. The vertical structure of the boundary layer was examined with multi-height aerosol measurements and also profile information up a large 280 m tower. We use this data to investigate the feedbacks between aerosols and radiation by challenging a large eddy model boundary layer dynamics with coupled aerosol-water-radiation interactions.