The Interlaken workshop in 1999 (EMEP, 2000) made a series of recommendations for measurements of particulate matter, and the first TFMM meeting in Vienna October 2000 built further on these conclusions and recommended a measurement program. This first TFMM meeting stressed the need for PM10measurements with a view to the current legislation in the European Union. The manual was adopted at the third TFMM meeting in Geneva 2002.
More measurement data within EMEP for assessment of the long-range transported part of the aerosol particulate mass in Europe are needed. This includes measurement of particulate mass, preferably determined according to EN 12341 (CEN, 1998), the reference method defined in EU Directive 1999/30/EC. In addition chemical characterisation and speciation of the particulate material is also highly desirable. Methods that give the added advantage of determining the chemical components in the sample are therefore recommended. The sampling period should be 24 hours and the samples should be changed daily together with the other sampling devices.
Different methods for the determination of aerosol particle mass have been extensively tested and compared (WHO, 1999; Guidance Document, 2001). Since different methods may give rise to systematic differences in the results, standardisation is necessary as specified by the European Union and the European Standards Organisation
EN 12341 specifies three reference methods for determination of PM10. Two of these, the high- and low-volume samplers, may be used at EMEP sites to obtain daily samples for weighing and subsequent chemical analyses. EN 12341 also gives detailed instructions with respect to comparisons, which are required to show that alternative samplers are equivalent to the reference methods for determination of PM10. These requirements are particularly relevant at sites where suspended dust and coarse particles form a major part of the airborne particulate matter. At many EMEP sites, however, particles < 2.5 mm may account for a large part of the total aerosol mass.
Direct recording instruments can be used if they have been shown to provide consistent results compared with gravimetric methods. They should be compared according to the CEN standard, preferably at the EMEP site and during all seasons and then used with possibly a correction factor. There are also instruments providing both gravimetric and online data measurements, which may be used if proven to give equivalent result to the standard. Monitoring with heated filters and/or inlets have a negative bias due to removal of water contained in the aerosol particles as well as evaporation of ammonium nitrate and semi-volatile organic compounds causing significant weight loss depending on season and location. It is difficult to avoid this problem even for standard gravimetric instruments where also losses of e.g. ammonium nitrate and semi-volatile organic compounds may occur during sampling and when filters are conditioned at constant RH and temperature. But to minimize evaporation artefacts it is recommended to use monitoring instruments with unheated inlets and/or filters.
One example of instrument, which is in accordance with CEN standard (1998) for PM10 measurements, is the high volume sampler SierraAndersen/GMW model 1200 seen in Figure 3.15.1.
Figure 3.15.1: Schematic diagram of Sierra-Andersen/GMW Model 12000 with a volumetric flow controller (VFC).
Without any special intake (hood) of the high volume sampler the upper cut is between 50-100 mm, termed as total suspended particle matter (TSP). An intake hood should be connected to collect particles of defined size (PM10); in practice this requires an impactor stage with a 50% cut-off at 10 mm a.e.d. When ambient air is drawn into the inlet, the acceleration nozzles fractionate particles larger than 10mm, which are impacted onto a greased collection shim. The air containing the PM10 particle fraction is channelled through to the filter holder. The flow rate is critical to maintain the PM10 cut point and when using the standard impactor dimension, following the criteria for the CEN standard (EN 12341:1998), a constant flow rate of 68 m3/h (1133 l/min) is needed for a high volume sampler and 2.3 m3/h (38 l/min) for a low volume sampler.
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Figure 3.15.3: Design of the 2.3 m3/h MVS PM10 sampling inlet (CEN, 1998).
The impaction nozzles and surface shall be cleaned and greased (e.g. with Vaseline) regularly, at least for every 20 samples. To facilitate cleaning and greasing the sampling inlet shall be constructed in such a way that the impaction plate can be pulled out of the housing. The construction and critical dimensions of the inlets of the high and low volume PM10 samplers are shown in Figure 3.15.2 and Figure 3.15.3.
The choice of filter type is dependent on instrumentation and what type of analysis is going to be done after sampling. For PM10 sampling, especially for high-volume sampling, it is necessary to use filter material with low flow resistance in order to maintain the prescribed flow rate. Quartz fibre filters should therefore be used for high-volume sampling. These filters have very good filtration characteristics with high flow and low pressure-drop, and their collection efficiency for small particles is excellent. The problem with the quartz fibre filters is their very large surface, and their adsorption of water vapour and other gases. Absorption of sulphur dioxide is not a serious problem when quartz fibre filters are used, but glass fibre and cellulose filters should not be used because of this possibility. Cellulose filters are also hygroscopic and are not suitable for particle mass measurements.
For low- or medium volume sampling, membrane filters may also be used, e.g. Teflon filters or filters made from mixed cellulose esters. But test should be carried out to see that this gives equivalent results.
When the amount of elemental- and organic carbon (EC/OC) is to be measured, sampling will have to be carried out on quartz filters. Membrane and cellulose filters contain organic material and are therefore unsuitable. Quartz filters do have the advantage that they can be baked at 500oC prior use, which may be necessary for measurements of the organic fraction to avoid high blank values. However heating filters may also result in evaporation of water in the filter structure; in addition, active sites are generated after baking the filters and volatile organic material will easier adsorb on the surface. Glass fibre filters will melt during the thermal process applied and cannot be used for sampling.
For mineral dust analysis however it is preferable to use membrane filters. Since quartz filters contain silicon and also has absorption problems when using X-ray techniques.
For heavy metal sampling, it is strongly recommended to use either Teflon or quartz filters. Glass filters do often have high blank values for certain elements.
Also cellulose filters have extensively been used for sampling of particulate matter followed by neutron activation analyses for mineral dust and trace metal analysis, but these filters cannot be used for weighing.
Positive interference may result from absorption of gaseous species, like SO2 and HNO3 on the filters followed by oxidation to sulphate and nitrate respectively. This problems increase with filter alkalinity. If alkalinity is less than 25 microequivalent/gram filters little or no sulphate artefact should occur (EPA, 1997). Nitrate formation from nitric acid occurs on many filter types, including glass fibre, cellulose ester and quartz fibre. Nitrate can also give negative interference due to dissociation of volatile ammonium nitrate. Semi-volatile organic compounds may also cause sample weight-loss. The magnitude is dependent on location and ambient temperature.
In addition to the general siting criteria given in Chapter 2, it is important that the inlet is located far from any obstruction that might influence on the airflow, like building walls and trees etc. Some pumps have shown to release particles e.g. copper. Air from such pumps should therefore be removed in a separate tube at least 10 metre from the filter intake.
It is very important that the filters are stored in filter holders or in plastic bags with zippers when it is transported between the laboratory and the field. Tweezers should be used, preferably made of non-metallic material or covered with Teflon at least when heavy metals are to be determined. Never touch the filters with the fingers. After exposure the high volume filters are folded in two with the exposed side against each other, put in transport container and transferred to the laboratory for conditioning and analysis, ensuring that the filters never is exposed to higher temperature than reached during sampling.
The sampling procedures are different from one air sampling system to another. Standard operating sampling procedures (SOP) should therefore be based on the samplers operator manual. Below some general points to remember is given:
The sampling equipment should be maintained in accordance with the manufacturers specifications. Accurate volume readings are important for the resulting measurements accuracy, and the volume meters need frequent calibrations. The flow rate should be checked using a rotameter. Calibrations should under no circumstances be less frequent than twice every year. The accuracy must be better than 5%. Written instructions for maintenance and calibration need to be available at the site, and the operator should be familiar with the contents.
All handling of filters should be made in clean air. All equipment should be stored in plastic bags in a dust free environment.
It is required by EN 12341 that the filters are equilibrated, at 20° C (±1) and 50% R.H. (±5), for 48 hours. This equilibration should be performed before the filters are weighed previous to the sample collection, and after sampling, before the filter is weighed again with the collected sample.
Exposed filters should immediately be left to equilibrate, or stored in a fridge or cooling room (<10oC) prior to equilibration. Care must be taken to avoid condensation of water onto the filter.
Some filters are brittle, and special precautions should be taken in their handling. All the handling of filters must be done using tweezers. If one has to touch the filters, always use anti-static powder free gloves.
Filters from the high-volume sampler should be weighed to the nearest 0.1 mg. For the medium or low volume sampler, a balance capable of nearest 1 mg, should be used.
Two reference filters should be kept in the balance room and their weight checked daily. Weight changes per week should not exceed a mass which corresponds to more than 0.1 mg/m3. If the changes are higher it might be an indication of a contamination in the conditioning/balance room. In addition one should daily weigh a standard weight to check the stability of the balance. These weights should be recorded in a logbook placed in the balance room.
Care should be taken to avoid electrostatic effects. It may be an advantage if the filters can be positioned in an upright position on the balance when the weighing is performed, at least for high volume filters. The use of ionising units, e.g. an alpha particle emitter (usually Polonium 210) is recommended, especially if membrane filters are used. For further guidance to the cause and control of static effects see: Cahn Technical Note: Static Control for Balances, 6/90. This document is available within the U.S. EPAs Ambient Monitoring Technology Information Center (AMTIC) PM monitoring information web page:
http://www.epa.gov/ttn/amtic/files/ambient/pm25/qa/static.pdf
One filter blank per week is recommended. The filter blanks are to be pre-equilibrated under the same conditions as the loaded filters, they should be transported to the site, inserted into a sampler without sampling, taken out and stored in the transport container in a shelter for the sampling period, taken back to the equilibration room and weighted. If the field blank exceeds a mass that corresponds to more than 0.3 mg/m3 it can be an indication of a contamination problem during transport or at the sampling site.
EN 12341 specifies three reference methods for determination of PM10 (CEN, 1998). Two of these, the high-volume sampler and a low -volume sampler, may be used at EMEP sites to obtain daily samples for weighing and subsequent chemical analyses. Commercial samplers that satisfy these specifications are given in the table below. Other samplers may also be used, provided that these give comparable results.
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Model |
Manufacture |
Low and medium volume sampler (Kleinfiltergerät) |
ISAP 1050 |
Ingenieurbüro
Schulze |
LVS3D/ |
Ing. Büro
Norbert Derenda, Bleibtreustrasse 7, |
|
LVS3/ |
Ing.-Büro Sven
Leckel |
|
High volume sampler |
ISAP 2000 |
Ingenieurbüro
Schulze |
ESM Andersen |
ESM Andersen
Instruments GmbH |
|
DA-80 H |
DIGITEL
Elektronik AG |
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Combined gravimetric sampler and beta monitor |
ADAM SM2000 |
Opsis AB, |
CEN (1998) Air Quality. Determination of the PM10 Fraction of Suspended Particulate Matter. Reference Method and Field Test Procedure to Demonstrate Reference Equivalence of Measurement Methods. Brussels (EN 12341).
EC (2001) Working group on particulate matter. Guidance to member states on PM10 monitoring and intercomparisons with the reference method. Draft Final Report, 16 March 2001
EMEP (2000) EMEP-WMO Workshop on Fine Particles Emissions, Modelling and Measurements, Interlaken, Switzerland, 2225 November 1999. Kjeller, EMEP/CCC-Report 9/2000
EPA (1997) Reference Method for the Determination of Particulate Matter as PM10 in the Atmosphere. Federal Registrer, 62, No 138, Appendix M to part 50.
WHO Regional Office for Europe, Copenhagen (EUR/ICP/EHB1040102, E62010, 10-13.)
WHO (1999) Particulate Matter (PM10 and PM2.5). Results of Intercomparison Studies. Conference Held in Berlin 3-5 September 1998.
To harmonize the measurements of particulate matter, the EMEP manual on PM2.5 and PM1 will to a large extent follow the coming reference from the European Community as it does for PM10. CEN is working on a reference method for PM2.5, but this is not expected to be finalized before earliest in 2004. Even though a reference method is not yet adopted it is highly desired to include the measurements of smaller particles as soon as possible. PM2.5 and PM1 has a larger fraction of long rang transported components than the PM10 which in many cases are influenced by local pollution and/or resuspension. Those countries interested in starting PM2.5 and/or PM1 measurements are encouraged to use one of the candidate CEN reference instrument and this manual for a general guidance on sampling and analyzing methods. For PM1 it is not yet any CEN group established to decide on a reference method, but one may still use any of the reference or candidate instruments for PM10 or PM2.5 with a PM1 inlet. Some companies manufacturing PM1 inlets are listed below.
Candidate Equivalence Instruments (automated)