OR/16/028 Introduction
| Beriro, D J, Field, L P and Cave, M R. 2016. Validation of a gravimetric PM2.5 impactor using particle sizing techniques. British Geological Survey Internal Report, OR/16/028. |
British Geological Survey (BGS) were appointed by DustScan Ltd (DustScan) to conduct the following work:
- Ambient air sampling for suspended particulate matter with an aerodynamic diameter (dae) of ≤2.5 µm (PM2.5) using the DS500X monitoring station;
- Scanning Transmission Electron Microscopy (STEM) analysis of the particulate matter that pass the size selective impactor and are collected on the filter media to quantify the size of individual particles; and
- Laser Diffraction (LD) granulometry of the oversize particulate matter collected on the impactor plate of the size selective impactor.
The purpose of this work was to provide DustScan with particle size analysis results that they can use to assist with the validation of their DS500X monitoring station fitted with a size-selective jet inlet impactor designed to collect PM2.5 suspended in ambient air.
This report summarises the results of PM2.5 sampling at Ballidon Quarry, Derbyshire and the associated analyses. The STEM and LD analysis were both designed to quantify the proportion of particles that are ≤PM2.5. These results are reported factually along with relevant observations made during the course of the work. The sampling and STEM analysis were conducted by BGS and the LD subcontracted to Escubed Limited (a company specialising in analytical services in colloids, particles and powder technology). There are no traceable reference standards for measuring PM2.5 so the methods adopted reflect good scientific practice in quantifying micro- particles collected at low sample masses.
The British Standards definition of PM2.5 is:
- “Particulate matter suspended in air which is small enough to pass through a size-selective inlet with
a 50% efficiency cut-off at 2.5 μm aerodynamic diameter” British Standard EN 12341:2014
- “Particulate matter suspended in air which is small enough to pass through a size-selective inlet with
The efficiency of the inlet of a size selective impactor may have a significant effect on the fraction of particulate matter surrounding the 50% cut-off point which affects the mass concentration of PM2.5 collected. The definition highlights that size selective impactors are not expected to collect particulate matter that is only <2.5 µm. This is because the morphology and density of individual particles is varied in environmental samples.