Available Projects

Rain is the atmosphere's main way of removing fine-particle pollution, yet it clears these particles 10 to 100 times faster than theory predicts, a puzzle since the 1950s. Working with the Met Office, you will test a new explanation: at these scales air no longer behaves as a smooth fluid. You will model particles of realistic shape meeting falling raindrops and deliver a better rain-scavenging scheme for weather and climate models.

Primary supervisor: Duncan Lockerby - Duncan.Lockerby@warwick.ac.uk
Co-supervisor: James Sprittles (Maths)

Project detail:
Every time it rains, the sky gets a wash. Falling drops sweep soot, dust and smoke out of the air, and this is the main route by which fine-particle pollution leaves the atmosphere. That matters: fine particles are the air pollutant most strongly linked to early death worldwide, and one of the largest uncertainties in climate projections, because they reflect sunlight and seed clouds. How long they linger, and how far they spread, depends on how efficiently rain removes them.

Here is the puzzle: for particles between about 0.1 and 1 micrometre (a hundredth of the width of a human hair), physics-based theory says rain should be almost useless at removing them. Measurements say otherwise: rain removes them ten to a hundred times faster than theory predicts, a discrepancy that has stood since the 1950s. This is not academic. In the Met Office's climate model, theory gives fine mineral dust an atmospheric lifetime of about 44 days; a scheme fitted to observations gives about 5.

This project tests an explanation nobody has properly examined. At the scale of these particles, air stops behaving like a smooth fluid: a particle is comparable in size to the distance an air molecule travels between collisions, so the classical equations of fluid flow no longer hold. Current models paper over this with a single correction factor dating from 1910, derived for spherical oil droplets in still air. Real soot and dust are not spheres, and a particle drifting up to the surface of a falling raindrop is not in still air.

You will build a new model of a single particle's random, jittering journey towards a falling raindrop, treating the air at the molecular level where it matters, for particles of realistic shape. From millions of these simulated encounters you will calculate how often particles are captured, and turn the answer into a rain-scavenging scheme that Met Office scientists, who helped shape this project, can test in their own weather and climate models.

You will gain skills in kinetic theory, stochastic simulation, rare-event methods and scientific computing, and see your work carried into operational environmental modelling. No background in atmospheric science is needed: the project suits a physicist, engineer or mathematician who wants their fluid dynamics to tackle a real environmental problem.

How to apply for admission: www.warwick.ac.uk/pgrengineering