Fine particles (aerosols) in the atmosphere have major impacts on human health and interact with the climate system through a range of different effects, either directly (by reflecting and scattering sun-light) or indirectly (e.g. by affecting the formation of cloud). The chemical composition of atmospheric aerosol is complex, especially the important contribution from organic aerosol, which itself is composed of thousands of different chemical compounds. These are either emitted directly (from fossil fuel combustion) or formed in the atmosphere (from gases either of biogenic or anthropogenic origin). In this project we are proposing to develop a new measurement system that can quantify the vertical fluxes (i.e. emission, deposition and formation) of organic aerosols. This system will be based on a recently developed Aerosol Mass Spectrometer system, incorporating a time-of-flight mass spectrometer, capable of detecting the full organic aerosol composition of atmospheric particles. By correlating this information with the vertical wind speed, we will be able to quantify organic aerosol fluxes and to derive information on the nature of the organic components that are moving up or down. We will deploy this instrument during four campaigns in three different environments, to (a) probe formation of organic aerosol above a Californian pine forest, (b) study fluxes of primary organic aerosol and the formation of secondary organic aerosol in the urban environment (through measurements from the BT Tower in London) and (c) to characterise organic aerosol formation above rain forest in Malaysian Borneo. The data will be analysed in the context of associated measurements of emissions of gases that may be involved in aerosol production (precursor gases), meteorological parameters and aerosol physical properties. From these data we will characterise the aerosol, quantify SOA formation and identify aerosol production mechanisms together with associated chemical time scales.