Positive bias caused by residual water in reference PM10 measurements

KornéLia Imre, ÁGnes Molnár, Viktor Dézsi, András Gelencsér

Research output: Contribution to journalArticle

Abstract

Dry aerosol mass concentrations (PM10, PM2.5) are determined after conditioning of the filter at t =20 ± 1 °C and RH=50 ± 5% for 48 hours according to the standard protocol EN 12341. The main result of this work is that applying the standard pre-conditioning step, complete removal of adsorbed water cannot be attained. In our experiment, aerosol samples collected in Budapest between November 2008 and March 2010 using a CEN (European Committee for Standardization) gravimetric sampler (Digitel, DHA-80) were studied. Following PM10 mass concentration measurements according to the EN 12341 protocol, we repeated the gravimetric aerosol mass measurements in the laboratory using a glove box after in-situ pre-conditioning for 48 h at t =20 ± 1 °C and RH < 30%. We assumed that at this low relative humidity all the adsorbed residual water was removed, and the absolute dry mass concentrations of PM10 could be determined (referred in the following as dry PM10 concentration). The mass concentration of adsorbed residual water, defined as the difference between the results of the standard and dry PM10 measurements, varied greatly in the range of 0.05–16.9 μg m-3. Expressed relative to the absolute dry PM10 mass concentrations, the residual water content in the standard measurement procedure amounted to 4.2 ± 1.5% and 7.9 ± 0.8% in summer and winter, respectively. In winter, relative contributions of adsorbed water as high as 33.2 m/m% was found. The significant seasonal differences as well as the large variations between individual samples may depend on various factors such as the chemical composition of the samples, particle load, and the RH history of the particles before and after sample collection. This last factor is expected to exert rather significant influence on the amount of adsorbed residual water, yet it is impossible to reconstruct. These findings have severe implications on reported dry PM10 mass concentrations using the EN 12341 protocol, especially in the winter period when most limit exceedances occur.

Original languageEnglish
Pages (from-to)207-216
Number of pages10
JournalIdojaras
Volume118
Issue number3
Publication statusPublished - Jul 1 2014

Keywords

  • Adsorbed residual water
  • Concentration
  • Dry mass
  • Low relative humidity
  • Standard protocol
  • Urban PM

ASJC Scopus subject areas

  • Atmospheric Science

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