Quantifying the health and climate impacts of vehicle particulate emissions

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Particulate matter (PM) is a key atmospheric pollutant regulated at the national and international levels. PM arises from solid and liquid particles directly blown into the air and from gases that condense into droplets. PM has been directly linked to increased mortality, especially the very small (<100 nm) particles which can inflame tissue deep in the lungs. One of the largest sources of PM in the UK is road traffic, which includes emissions from engine exhaust, as well as tyre and brake abrasion and lofted dust from the road surface. Over the past two decades, the amount of PM emitted from traffic has decreased substantially due to regulations pushing for cleaner internal combustion engines in vehicles. However, as the number and weight of vehicles on the road increases, more particles from non-exhaust sources (e.g. tyres and brakes) are emitted. Unlike fossil fuel combustion byproducts, these particles are not well characterised. It is unknown, for example, what driving conditions enhance the production of non-exhaust particles, whether the particles are small enough to affect human health, and how these particles interact with gases in the atmosphere. PM produced by human activity is also an important contributor to changes in climate. Soot particles produced by fossil fuel combustion, including those found in the exhaust of diesel and petrol vehicles, absorb sunlight and enhance the net warming of the planet. Particles from other sources, such as condensed gases, can have a cooling effect on the climate by reflecting sunlight. Reflected sunlight is measured by satellites to map out the PM levels across the globe. In order to accurately determine PM concentration from satellite measurements it is important to understand how different types of particles interact with light. This information is also vital for predicting future changes in climate using computer simulations of the atmosphere. As the types of particles produced by road traffic changes over time, the interactions of these particles with incoming sunlight will be affected. In this research project, I will build three instruments to better understand characteristics of particles produced by road traffic in a typical UK city centre. The first instrument will measure the sizes of the particles - information directly relevant to public health officials who can focus future pollution reduction efforts on areas where very small particles are detected. The other two will measure the light absorbed and reflected by the particles in air. These data are useful for checking the accuracy of calculations used to predict future changes in climate and information reported by satellites. Additionally, we can combine this information with existing measurements of gases to better understand the chemistry of the urban atmosphere since gases and particles are closely linked.