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

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 science

1) 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).

Five stakeholders:
1) Climate modellers:
The research will provide an algorithm for climate modellers to incorporate the effect of core-shell aerosol in atmospheric aerosol layers in their climate models and potentially new data for future IPCC reports. Researchers at the Met. office and MPIC are end users of the work and project partners. Thus, reducing the uncertainty in the level of scientific understanding of modern climate change. To achieve this, we will use the traditional method of publishing papers, presenting the work at conferences with the likely target audiences, and newsletters/factsheets to modelling research groups. Our main conference will be the AGU and EGU meetings where we can present our work at three separate sessions (Climate modelling, Atmospheric aerosol, and Remote sensing). The PI has decided against working with just one modelling group in order to get the data out quicker to more modellers. A grant-specific website page from the main departmental page will contain the raw data and models for two years and will then be moved to the CERN data centre Zenodo.org which will provide data curation and a DOI. To alert the modelling community we shall publish an article of our work in EOS and undertake a press-release and hold a one-day meeting at Burlington House on "core-shell aerosol" to push the results from this and similar research to a wider important audience. Previous one-day meetings hosted at Burlington House have attracted policy makers and workers from DECC.

2) Earth Observation workers: The Earth observation community will receive: (1) a top of atmosphere and bottom of atmosphere Bi-directional Reflectance Factor model for core-shell aerosol effects in the optical wavelengths. The workers will be alerted by a direct mail and invite to the London workshop described above. This work would directly provide data and models for this industry which is worth millions to the UK economy.

3) UK science: The PI has identified ~20 research groups from climatologists to atmospheric chemists who are directly interested in this work. The PI will provide travel money for a representative of each of these groups to attend a workshop. A sum of £2,500 is requested to provide rail fares, flights and subsistence for a day. We will build a network across several disciplines. The initial network can be followed up as an on-line community hosted on the RHUL website.

4) School age children: The PI has always felt it important to publicise his research with schools. With this grant the PI wishes to explore a less orthodox, more risky, but potentially wider form of outreach. A commercial children's illustrator has been approached to produce an educational picture book on atmosphere and the global threats from atmospheric climate change. The PI will provide the narrative. The book will be given away free on Amazon books. We have budgeted £9500 for the illustrator, a print run for local schools and dissemination.

5) Young adults: The PI uses some of his old NERC sampling equipment to support his PhD students in the British Schools Exploring society who take young adults to a polar environment every year for 5 weeks as science leaders. We aim to repeat this study and find this an exciting way of influencing young adults just before they plan to go to University. During the 5 week long expedition they will conduct a scientific investigation to educate the young adults about modern climate change, as well as teaching them to live and survive in the Arctic. The project will investigate the amount of brown carbon aerosol deposited on the Sveabreen glacier, Svalbard. The young adults will collect snow samples, melt them and filter out the brown carbon using quartz filters. The brown carbon remains on the filter and comparing with standards made in the lab they will be able to quantify ng g-1 concentration of brown carbon in snow based on a technique published by Warren and Grenfell (2009).