Particle concentrations: from CERN to Leeds to the free troposphere
Dr Hamish Gordon, Dr Jim McQuaid
Ultrafine particles in the atmosphere are critical to air quality and climate, as they form the seeds of cloud droplets and penetrate deep into the human body. Most of the sub-100nm diameter particles originate from new particle formation. This process starts with the formation of clusters when gas molecules such as sulphuric acid collide and stick together, then other gas molecules condense onto and grow the clusters into new atmospheric particles.
Recent experiments at the CLOUD experiment at CERN have substantially improved our understanding of new particle formation. The results have now been included in a global aerosol model (e.g. Dunne et al, Science 354 1119 (2016)). The purpose of this project is to investigate how well the particle number concentrations predicted by the model represent particle number concentrations in the atmosphere, by comparing the model to atmospheric measurements.
Ultrafine particles are measured by aircraft and at fixed observation sites by condensation particle counters (CPCs). These condense low volatility vapours onto the finest aerosol particles to grow them to the size where they can be counted with a laser beam. The largest particles can be seen directly with a laser inside an air quality monitor.
To gain familiarity with particle counting and planning atmospheric observations, Dylos 1700 air quality monitors will be deployed by the student during the project to collect data on larger particles in various environments in Yorkshire. The PM2.5 concentrations obtained will be compared with the model. These measurements will also yield valuable insights into the rest of the observation data (ultrafine particle concentrations).
To these measurements will be added data from the GASSP (Global Aerosol Synthesis and Science Project) from around the world collected, for example, on selected commercial Lufthansa flights, on dedicated aircraft campaigns, on ships and at surface stations (http://gassp.org.uk/data/). The student will take model simulations with data from the CLOUD experiment and compare the particle numbers to these measurements. This will feed back to the CLOUD experiment, as we will be able to determine the environments where the CLOUD data are incomplete.
The project will suit a student with a quantitative background, comfortable with programming using Python.