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ECN publication
Sampling of PM10 at high relative humidity
Published by: Publication date:
ECN 1-4-2000
ECN report number: Document type:
ECN-C--00-061 ECN publication
Number of pages: Full text:
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PM10 contains hygroscopic components which attract water. Due to thiswater uptake particles which actually belong to PM10 may become so large that they are not collected in PM10 sampling. This loss is not considered in calculations of the PM10 concentration, which leads to an overestimate of the modeled PM10. The Netherlands Energy Research Foundation (ECN) was asked to identify the major factors influencing the hygroscopic growth of PM10 in the Netherlands and to provide an estimate of the loss in sampling of PM10 at high relative humidities. It was found that the dominant hygroscopic aerosol components in the Netherlands are sulfate/nitrate and sea salt. Sulfate and nitrate (in the form of ammonium sulfate and ammonium nitrate) are typically present in particles with a dry diameter smaller than 2.5 mum. Such small particles only grow to droplets with a size larger than 10 mum in situations with fog. It is shown that the non-hygroscopic material should also be present in the fog-droplets. This means that most PM is not sampled during fog. With the given frequency of fog in the Netherlands, this leads to the estimate that on an annual basis of 5% of PM10 is missed during sampling. Since PM10 values are expected to be high on foggy days, much larger differences between modeled and measured peak values of PM10 are projected. Little sea salt will be missed in PM10 sampling, because it is not present in fog/sea mist. 8 refs.

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