Particulate matter and why it matters
The air that we breathe is full of particles. It can’t be avoided. City or village, farmland or beach, there will be some trace of dust, soot, pollen, smoke or even liquid particles like sea-spray. What varies enormously is the level of particulate matter (PM). In measuring this, the common standard is PM2.5 which means particles no larger than 2.5µm in diameter. To put this in context, it doesn’t include dust mites which are a full 3µm across and certainly not bits of hair which range from 100 to 150µm in diameter.
There is no safe level of PM2.5 – just the lower the better – although the WHO recommends that concentrations should not exceed an annual average of 10µg/m3 and a daily average of 25µg/m3. Increased levels of PM2.5, whether permanent or temporary, have serious effects on public health, exacerbating lung and heart conditions. Children, the elderly and people with existing respiratory or cardiovascular conditions are, not unexpectedly, particularly affected.
The University of Leicester, which has a history of air quality research, collaborated with aerial survey specialists Bluesky on a project to calculate the benefits of green infrastructure within urban areas in reducing PM2.5. Trees and grassy areas have obvious immediate benefits in making urban environments more pleasant places to live, work and play – but they can also have practical benefits in reducing particulate matter, which they do in two ways: dispersion and deposition. Dispersion is reducing the concentration of particulate matter by breaking it up and spreading it over a wider area. Whereas in deposition particles remove themselves from the air by attaching to surfaces.