In 2014-16 Dr Abigail Whitehouse conducted research looking at pollution in London and its impact on the health of children in the city. Dr Whitehouse went to schools all over London collecting sputum samples from hundreds of children between the ages of 9-14. The children inhaled a saline (salty) solution to loosen the mucus in their lungs and then coughed up a sample. The samples were then analyzed and photographed through a microscope. Different cells can be identified, and in some images black carbon particles, which comprise the core of PM10 and PM2.5, are visible.
Aside from the impact of Covid19, air pollution levels in London haven’t changed significantly since the research was conducted, and this particular technique has been shown to reflect pollution levels over time. It is likely the results would be the same today.