Case Study

St. Peter's School

The school is based in the City of Westminster, which has the worst air pollution in the Country (as per Particle pollution levels in the Borough have been known to exceed 100μg/m3.

The World Health Organisation’s guidelines for annual exposure to PM2.5 is 10 μg/m3.


St. Peter’s is in a Victorian era two storey building with a playground at the front. There is no centralised heating or ventilation system. Heating is provided by a mixture of radiators and individual room heaters.

The proposal was that, at no cost to the school, Evergen shall –

  • monitor air quality in all areas of the school using a precision sensor. The pollution readings will be made available via an online dashboard
  • once the pollution levels in all areas of the school had been established, the school will propose one room where Evergen will install their free standing PureAire cleaners
  • monitoring will continue in that room to demonstrate the improvement in air quality
  • in collaboration with the School, Evergen will then meet potential sponsors, investors and stakeholders to help raise the funds to provide clean air across the whole school including outside


Evergen partnered with EarthSense ( to monitor air quality. EarthSense is a leader in accurate air quality monitoring, modelling and visualisation. EarthSense products and services are behind some of the best air quality initiatives in the UK. Evergen provided a Zephyr EarthSense monitor to St. Peters to establish independent and accurate monitoring of air quality at the school, before and after installation of Evergen’s PureAire technology. The portable Zephyr sensor can measure the main pollutants NO, NO2, O3, PM1 PM2.5 and PM10 and provides the data on an online portal.

Monitoring was conducted over a period of four weeks with the school moving the sensor around various parts of the building and a daily log was kept of the dates and locations. Once sufficient data had been collected there was some discussion as regards where the demonstration units should be installed as the school felt that choosing one classroom may upset parents whose children were in the other classrooms.

Consequently the main hall was chosen for the demonstration as this was used by all children throughout the day for assembly, games and during lunchtime. This was a much large room so three Evergen PureAire units were installed to cover the area.


The results showed a dramatic reduction in NOx and PMs. The surprise was the significant reduction in O3. The Evergen PureAire system actually reduced the background Ozone levels by 83%.

Measurements taken before installation of PureAire system

Measurements taken after installation


Evergen’s high efficiency PureAire System has achieved and maintained a huge reduction in PMs (particle pollution as well as harmful gas pollutants. As PureAire system does not use filters to remove particles, this performance will be maintained for many months.

"This problem is not unique to St Peter’s - all schools in London are being affected by rising pollution levels. This technology could not have come soon enough, and I’m delighted to see it making such a measurable difference to the air quality in the school."

Miles Ridley, St Peter’s Headteacher