New Strategies for Sampling, Analysing and Understanding Aerosols

Aerosols are a collection of solid particles of liquid droplets dispersed in air and include smoke, fog, sea spray and pollution particles from vehicles. Particle sizes can range from the nanometre (a millionth of a millimetre) to the millimetre scale. Aerosols influence health, visibility, and climate and are finding increased technological application in the delivery of drugs to the lungs, the engineering of nanostructures through spray drying, and the delivery of fuels for combustion. This research will examine some of the fundamental challenges faced in understanding aerosols.A key to understanding the impact of aerosols on human health is to understand how they are transformed as they are inhaled and exhaled. In the humid environment found within the respiratory tract, water vapour can condense on inhaled particles leading to growth in size. This can influence their depth of penetration into the lungs, with smaller particles penetrating deeper. The targeted delivery of drugs to the lungs may be enhanced by altering their response to a humid environment. Further, the transmission of airborne viruses, such as the influenza virus, may be influenced by the humidity changes on exhalation and inhalation. Similarly, in atmospheric science it is crucial to understand how aerosol particles are influenced by humidity in order to predict the size of cloud droplets. Understanding the change in particle size with humidity is also critical for understanding the ability of particles to scatter and absorb sunlight and their impact on climate. Thus, key themes of this project will be to understand how particles change in size with humidity and their efficiency in scattering and absorbing light.It is also essential to know the chemical composition of particles to interpret their impact on health and the environment, particularly in polluted urban environments, and to understand how particles are chemically changed over time. Water is ubiquitous in our environment and largely regulates the composition of aerosol. However, many chemicals are not soluble in water. This is particularly true for many pollutants such as polycyclic aromatic hydrocarbons, which are considered to be carcinogenic and mutagenic, and for many of the agrochemicals that are used in crop production. Such chemicals may be very soluble and become concentrated in organic liquids. A key theme of this project will be to understand the properties of aerosol droplets that contain both water soluble and insoluble chemicals, and to understand how chemicals can dissolve into the organic phase within an aerosol. Indeed, many of the organic components may undergo chemical reactions in our environment and a further theme will be to explore the chemistry that can occur in aerosol and how it influences aerosol properties. From the delivery of drugs to the lungs, to the evaporation of fuel droplets in combustion, the spray drying of particles, and the growth of particles in the atmosphere, understanding the rate at which particles can change size and composition is also crucial. For example, the processes occurring during the evaporation of a volatile solvent in the use of metered does inhalers critically determine the delivery of active pharmaceuticals to the lungs. The solid structures formed when liquid droplets rapidly evaporate are controlled by how quickly the solvent evaporates in spray drying. Studies of these very rapid processes are a further theme.Finally, there is considerable interest in the analysis and chemical reactions of very small sample volumes, and this has led to the development of lab-on-a-chip technology. Commonly, solutions flow through very small fabricated channels to allow measurements on micro-litre samples. A final theme of this project will be to control reactions in aerosol droplets containing only picolitres of sample, a billionth of cubic centimetre, using laser beams to move particles around and control chemistry.