Quantifying the light scattering and atmospheric oxidation rate of real organic films on atmospheric aerosol

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The proposal presented here is important for quantifying how interfacial chemistry in the atmosphere is important in the assessment of modern climate change. It relies on three aspects of atmospheric science1) Atmospheric aerosols are tiny solid or liquid particles suspended in air. They arise from human activity (e.g. burning of fossil fuels) and naturally (e.g. breaking ocean waves) and can exist in the atmosphere for minutes to days. These aerosol are a large source of uncertainty when assessing man-made contributions to climate change as they strongly influence (I) the amount of light reflected back to space (potentially cooling the planet) and (II) the formation of clouds, and how much sunlight they reflect back to space (again, potentially cooling the planet). 2) Some of these aerosol have thin films or coatings of organic material. As the size of these aerosol are similar to the wavelength of sunlight a thin coating can significantly alter their ability to scatter and 'reflect' sunlight and their potential to form clouds. 3) The atmosphere effectively acts as a low temperature, dilute fuel, combustion system oxidizing chemicals released from the Earth's surface. The rate at which chemicals released from the Earth's surface can be removed by oxidation is important in understanding the atmosphere's self-cleansing mechanism.Previously *proxies* of thin films on atmospheric aerosol have been shown to potentially alter the light scattering and cloud forming ability of clouds. These proxies have been chosen from a chemical catalogue and do not represent the mixture and variety found in the atmosphere. We will use *real* material extracted from different locations to characterize the thin films formed on real atmospheric aerosol, determine their film thicknesses, light scattering ability and their chemical reactivity in the atmosphere. Our own preliminary work demonstrates that laboratory proxy thin films are not representative of the real atmosphere. The film thicknesses are critical to the calculation of their light scattering ability which in turn is critical to calculation of the proportion of sunlight scattered back to space. The chemical reactivity is important in determining the lifetime of the film, because as the film reacts the optical properties of the particle will change significantly. If the film lifetime is longer than a typical aerosol lifetime then it can be simply included into atmospheric models, but if the film lifetime is much shorter then it may be ignored. However preliminary data suggests it is has a similar lifetime meaning the *changing* light scattering properties of a coated particle will need to be modelled.The project represents the first comprehensive study of atmospheric thin film oxidation and light scattering with real atmospheric matter from the atmosphere. The combined experimental and modelling approach will allow the demonstration of (I) core-shell (thin film behavior) from atmospheric samples, (II) calculation of their optical properties and change in radiative balance at the top of the atmosphere., (III) measurement of atmospheric oxidation rates of the film and inclusion in Co-I led complex aerosol kinetic modelling of complex mixture aerosol. The proposal will also continue to develop two emergent exciting techniques for atmospheric science: Laser trapping with Mie spectroscopy and neutron scattering. The ability of these technique to study films ~10nm thick in real time, with the correct morphology and with unprecedented precision is phenomenal. The proposal will also be an excellent training vehicle for two PDRAS in soft-matter, facility, and atmospheric experimental science with real world modelling of atmospheric outcomes.The data and model systems from this proposed work will be ready for including global climate models. The letters os support demonstrate that ends users for some off data with the Met. office(UK) and MPIC (Germany).