Gravimetric analysis of air filter samples
By Owen Butler, Health & Safety Laboratory, Technical Advisor to the LGC-HSL AIR PT scheme
The measurement of airborne particulate matter, PM10 and/or PM2.5 particle size fractions, in ambient air is defined for European regulatory purposes by the European Committee for Standardisation (CEN) standard EN 12341:20141, a gravimetric filter-based method. Similar procedures have been published elsewhere such the US EPA Federal Reference Method2 for the determination of fine particulate matter as PM2.5 in the atmosphere. These procedures involve the following steps:
- Conditioning and pre-weighing filters under controlled laboratory conditions using a micro-balance.
- Packing and sending filters for air sampling
- Receiving, conditioning and post-weighing filters
- Calculating the particulate mass sampled as the difference between post- and pre-weighing values and a corresponding particulate mass per unit air volume value
Along similar lines, gravimetric filter-based methods are also used in other air sampling arenas such as workplace and stack air monitoring programmes.
Existing samples 3, 4 and 40, filter samples spiked with a known mass surrogate, are available within the AIR PT program to test the competency of laboratories undertaking gravimetric analysis in the workplace and stack air monitoring environments. Here filter samples are sent to participants for pre-weighing, returned for spiking and then re-sent to participants for re-weighing i.e. replicating as far as is possible the filter weighing process that is routinely carried out.
A new trial sample 17 has been introduced into the Air and Stack Emissions PT scheme which will allow laboratories to assess their performance in weighing ambient air filters to requirements set out in EN 12341. Here 4 x 47 mm diameter quartz-fibre filters loaded with a mass surrogate in the range 0.2 – 8 mg, will be supplied alongside 3 x blank quartz-fibre filters. It is proposed that these new test materials will be dispatched to participants in round AR023 scheduled for November 2017.
- EN 12341:2014 Ambient air. Standard gravimetric measurement method for the determination of the PM10 or PM2,5 mass concentration of suspended particulate matter
- US EPA FRM 1997: Reference Method for the Determination of Fine PM as PM2.5 in the Atmosphere, 40 CFR 50, Appendix L.