OpenLegislation

Division Problems in mass concentration measurements of PM2.5

United Kingdom

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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.