Calculating how trees improve urban air quality
Simulating the City of Leicester
Since it’s not really practical to crawl around a city centre measuring numbers of microscopic particles, this research required some sophisticated computer modelling. A 2km by 2km square of Leicester (the city centre and the surrounding area) was modelled in detail, starting with a 3D LIDAR model originally constructed in 2007 with a resolution of 25cm. Trees were added, based on the average urban tree density for the East Midlands, modelled as porous objects using Bluesky’s National Tree Map Crown Polygon software. Areas identified as grass (based on Ordnance Survey mapping) were modelled at a surface roughness of 0.03m while non-grass areas were modelled at a roughness of 0.10m, thereby providing an approximation of things like bollards and benches.
The wind was simulated at two different speeds - 4.6m/s (the UK average) and 1m/s – and from a clock-face of 12 different directions at 30 degree intervals. The research considered different combinations of data, such as just the city centre, just the surrounding areas or just roadsides. After some serious number-crunching, what this research showed was an average 9.0 percent reduction in PM2.5 caused by the aerodynamic dispersive effects of trees. Deposition on trees resulted in a 2.8 percent reduction in PM2.5 but deposition on grass only reduced PM2.5 by 0.6 percent.
This research – more detailed and over a larger area than any previous similar projects – was the first output from EarthSense Systems, a spin-out company established as a collaboration between BlueSky and the University of Leicester. EarthSense Systems aims to deliver products that enable the world to visualise and solve its air quality issues, providing policy makers, planners and those responsible for delivering results, with access to real world information in order to support decision making.
With a mix of hardware (air quality sensors), software (bespoke modelling), data (derived and complementary) and people, EarthSense is uniquely poised to take a lead in air quality monitoring solutions and services, making a difference to people’s lives and delivering high value information to a range of consumers and decision makers. Among a range of projects, EarthSense is providing a network of Zephyr sensors to Berlin to assist with a major initiative to understand NO2 and O3 concentrations across a diverse environment.