ANNEX

GUIDANCE ON PM2,5 MEASUREMENT UNDER DIRECTIVE 1999/30/EC

The purpose of this document is to give recommendations to air quality managers and network operators on the selection of PM2,5 measurement devices required by Directive 1999/30/EC for fine particles. These recommendations do not apply to other possible applications with different measurement objectives, as for example in the case of research activities, or in the case of indicative measurements.

Background and CEN standardisation work

Directive 1999/30/EC states in Article 5 that ‘Member States shall ensure that measuring stations to supply data on concentration of PM2,5 are installed and operated. Each Member State shall choose the number and the siting of the stations at which PM2,5 is to be measured as representative of concentrations of PM2,5 within that Member State. Where possible sampling points for PM2,5 shall be co-located with sampling points for PM10 ’. Article 7 further mentions that ‘The provisional reference method for the sampling and measurement of PM2,5 shall be laid down in Section V of Annex IX.’ Annex IX finally asks for the preparation of a guideline to be developed by the European Commission in consultation with the committee referred to in Article 12 of Directive 96/62/EC.

DG Environment has given a mandate to CEN to develop a standard European reference method for the measurement of PM2,5. This method is based on the gravimetric determination of the PM2,5 fraction of particles in air, sampled at ambient conditions. CEN TC 264/WG 15 started its work in 2000. Field validation campaigns have been carried out in eight European countries, namely Spain, Germany, The Netherlands, Austria, Italy, Sweden, the United Kingdom and Greece and have been completed in summer 2003. The final CEN standard method will therefore not be available before 2004.

CEN WG 15 is currently testing various candidate devices based on the gravimetric determination method and equipped with different inlet types from European manufacturers as well as the US Federal Reference sampler:

—	MINI-WRAC, single filter sampler, from Fraunhofer Institute for Toxicology and Aerosol Research (FhG-ITA), Germany,

—	US-Federal Reference sampler, single filter sampler: RAAS 2,5-1, from Thermo Andersen, USA

—	Partisol FRM Model 2000, from Rupprecht and Patashnick, United States of America,

—	Partisol plus Model 2025-SCC, sequential sampler, from Rupprecht and Patashnick, United States of America,

—	LVS-3D, single filter sampler, from Derenda, Germany,

—	SEQ 47/50, sequential sampler, from Leckel Company, Germany,

—	HVS-DHA 80, sequential sampler, from Digitel, Switzerland.

In addition, CEN is also testing a number of automated measurement devices, based on the beta ray attenuation method and the tapered element oscillating microbalance (TEOM), to develop test procedures for equivalency with the reference gravimetric method:

—	ADAM, beta ray attenuation, sequential, from OPSIS, Sweden,

—	FH 62 I-R, beta ray attenuation, filter tape, from ESM Andersen Company, Germany,

—	BAM 1020, beta ray attenuation, filter tape, from Met One, United States of America,

—	TEOM SES, sharp cut cyclone, from Rupprecht and Patashnick, United States of America.

Problems in mass concentration measurements of PM2,5

Several problems, partially known from previous experiences with PM10 measurements, have to be taken into consideration when determining PM2,5 mass concentrations. Preliminary inter-comparison studies carried out in a number of EU countries have shown significant differences between the results of manual PM2,5 samplers, ranging up to ±30 %. Reasons for the observed differences between the samplers are complex and can be divided into:

—	artefacts on the filter, e.g. evaporative losses during sampling or conditioning of the filter,

—	artefacts in the size fractionating inlet, e.g. poor design, changes of the cut-off due to poor volume flow control and particle deposition on the impaction plate,

—	artefacts due to the sampling system set-up; e.g. particle deposition in the sampling tube (especially for long or curved tubes).

It has to be noted that the chemical composition of PM2,5 is significantly different from that of PM10 especially the semi-volatile particulate matter (e.g. ammonium nitrate, organic compounds) is enriched in the fine PM2,5 size fraction. The particulate matter in the size range between PM10 and PM2,5 mainly consists of inert components such as silica, metal oxides, etc. Hence the problems with losses of semi-volatile matter already observed when sampling PM10 may be even more pronounced for PM2,5 measurements.

Losses will essentially depend on the composition of the aerosols and the presence of volatile particulate matter, as well as on the difference between ambient and sampling temperatures. The losses may therefore present important seasonal and geographical variations. As an example of this, losses close to 0 % were reported in Scandinavia during a spring episode (aerosols from road sanding), whereas losses up to 70 % were observed in Central Europe during a winter episode (aerosols with high ammonium nitrate content).

With this background it can be anticipated that any heating of the sampling system will show significantly lower PM2,5 mass concentrations than a system kept under ambient conditions.

Recommendations for monitoring PM2,5

In the absence of conclusions from the CEN standardisation activities, the following recommendations for PM2,5 can be given:

Regarding the measurement method

The mandate given by the Commission to CEN specified that the measurement method to be standardised is based on the gravimetric determination of the PM2,5 mass fraction of particulate matter collected on a filter under ambient conditions. Other methods, such as the beta ray attenuation method and the tapered element oscillating microbalance (TEOM), are currently tested for equivalence with the gravimetric method by CEN WG15.

Regarding the PM2,5 specific inlet

Currently there are two main inlet designs available and in use for monitoring and research purposes: the impactor type inlet and the sharpcut-cyclone type. Various inlets of both types are currently under testing e.g. within the framework of CEN WG 15. The size fractionation efficiency of the inlet needs to ensure that 50 % of the particles with an aerodynamic diameter of 2,5 μm are collected on the filter.

Regarding the instruments

Theory and former experience gained in the PM10 validation work suggests that the use of devices whereby the sampling probe and/or filter is heated during collection should be avoided for the measurement of PM2,5. In order to limit as far as possible the losses of volatile particles, instruments sampling as close as possible to ambient temperature should be preferred for PM2,5.

Considering the incomplete manner and the lack of coherence of the results obtained thus far from the various studies, it is impossible for the present to select candidate instruments for the monitoring of PM2,5. When it comes to the selection of a particular measurement device, a careful approach is recommended. Preference should be given to an approach that does not entail important resource investment and that allows for the adaptation of the measurement requirements to future developments (e.g. the forthcoming European standard method on PM2,5 measurements, technical developments by instrument manufacturers, the upcoming regulation on heavy metals).

When reporting PM2,5 data, it is essential to document fully the measurement methodology that was used to generate the data.