Dynamic Surface Properties of Atmospheric Aerosol and Resulting Climate Impacts

Abstract:
Atmospheric aerosols affect climate by direct scattering or absorption of solar radiation and indirectly, by serving as Cloud Condensation Nuclei (CCN) and forming cloud droplets. Atmospheric aerosols provide the largest negative radiative forcing, whilst remaining as the contribution with the largest uncertainty. The surface properties of atmospheric aerosol are crucial due to their high surface-to-volume ratios, whilst determining the fraction of atmospheric aerosol that may form cloud droplets. Most climate models still assume that activating CCN have a surface tension equivalent to pure water, but current experimental validation of this assumption is insufficient. Surfactants found in the atmosphere may depress the surface tension of droplets below that of water, as found in field measurements, whilst size-dependency of droplets is another contributing factor to their dynamic surface tension. The proposed research will investigate the dynamic surface tension and surface-bulk partitioning of surfactants within picolitre droplets using two experimental approaches, both used to evaluate damped oscillations observed in droplets. First, droplet coalescence using holographic optical tweezers will investigate surface tension of droplets at equilibrium surface composition and surface tension, considering size-dependency of their surface-bulk partitioning of surfactants. The second method will evaluate surface-bulk partitioning timescales for surfactants in droplets with fresh surface ages (sub-millisecond), whilst assessing the significance of the partitioning process on their dynamic surface tension. These experimental data will be shared with collaborators to modify monolayer partitioning models and thus, to improve climate modelling estimates, reducing uncertainty found in aerosol-related radiative forcing projections.

Aerosol science has a significant impact on a broad range of disciplines, extending from inhaled drug delivery, to combustion science and its health impacts, aerosol assisted routes to materials, climate change, and the delivery of agricultural and consumer products. Estimates of the global aerosol market size suggest it will reach $84 billion/year by 2024 with products in the personal care, household, automotive, food, paints and medical sectors. Air pollution leads to an estimated 30-40,000 premature deaths each year in the UK, and aerosols transmit human and animal infections. More than 12 million people in the UK live with lung disease such as asthma, and the NHS spends ~£5 billion/year on respiratory therapies. Many of the technological, societal and health challenges central to these areas rely on core skills and knowledge of aerosol science. Despite this, an Industrial Workshop and online survey (held in preparation for this bid) highlighted the current doctoral skills gap in aerosol science in the UK. Participating industries reported that only 15% of their employees working with aerosol science at doctoral-level having received any formal training. A CDT in aerosol science, CAS, will fill this skills gap, impacting on all areas of science where core training in aerosol science is crucial.

Impact on the UK aerosol community: Aerosol scientists work across governmental policy, industrial research and innovation, and in academia. Despite the considerable overlap in training needs for researchers working in these diverse sectors, current doctoral training in aerosol science is fragmentary and ad hoc (e.g. the annual Fundamentals of Aerosol Science course delivered by the Aerosol Society). In addition, training occurs within the context of individual disciplines, reinforcing artificial subject boundaries. CAS will bring coherence to training in the core physical and engineering science of aerosols, catalysing new synergies in research, and providing a focal point for training a multidisciplinary community of researchers. Working with the Aerosol Society, we will establish a legacy by providing training resources for future researchers through an online training portal.

Impact on industry and public-sector partners: 45 organisations have indicated they will act as CAS partners with interests in respiratory therapies, public health, materials manufacturing, consumer and agricultural products, instrumentation, emissions and environment. Establishing CAS will deliver researchers with the necessary skills to ensure the UK establishes and sustains a scientific and technical lead in their sectors. Further, it will provide an ideal mechanism for delivering Continuing Professional Development for the existing workforce practitioners. The activity of CAS is aligned to the Industrial Strategy Challenge Fund (e.g. through developing new healthcare technologies and new materials) and the EPSRC Prosperity Outcomes of a productive, healthy (e.g. novel treatments for respiratory disease) and resilient (e.g. adaptations to climate change, air quality) nation, with both the skilled researchers and their science naturally translating to long-lasting impact. Additionally, rigorous training in responsible innovation and ethical standards will lead to aerosol researchers able to contribute to developing: regulatory standards for medicines; policy on air quality and climate geoengineering; and regulations on manufactured nano-materials.

Public engagement: CAS will provide a focal point for engaging the public on topics in aerosol science that affect our daily lives (consumer products, materials) through to our health (inhalation therapeutics, disease transmission and impacts of pollution) and the future of our planet (geoengineering). Supported by a rigorous doctoral level training in aerosol science, this next generation of researchers will be ideally positioned to lead debates on all of these societal and technological challenges.