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Title:
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Report Laboratory tests on measurement of IONS in PM2.5
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Author(s):
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Published by:
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Publication date:
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ECN
Environment & Energy Engineering
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10-2-2015
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ECN report number:
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Document type:
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ECN-O--14-049
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Other
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Number of pages:
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Full text:
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35
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Download PDF
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Abstract:
This report represents the results acquired under WP2 of the method validation project for anions and cations in PM2.5. WP2 was dedicated to the laboratory tests comprising the ruggedness test and the EMEP equivalence test. The ruggedness tests were focused on the artifact induced by volatile inorganic substances and performance of the various filter analysis methods.
Preloaded quartz filters with mixtures of NH4NO3 and (NH4)2SO4 were prepared. Subsequently the filters were exposed to sampling conditions that were expected to lead to evaporation. By measuring on line the extra NH3 and HNO3 behind the filter we were able to observe the evaporation velocity characteristics of NH4NO3. Apparently two different phases of evaporation exist, a high rate phase followed by a low rate phase. The high velocity rate is in the order of 20 ug/hour and the low rate in the order of 2 ug/hour. It is assumed that the latter represents evaporating NH4NO3 with affinity to the quartz filter material. The transition between both phases is dependent on the quantity of NH4NO3 on the filter and the relative humidity (approximately 80 ug at 40% rH and 230 ug at 75% rH). The velocity at the high rate phase correlates with the calculated deficit of NH3 and HNO3 when compared to the atmospheric equilibrium concentrations. This relationship could not be found for the low velocity phase. The average amount of NH4NO3 seen at the WP3 field trial would have been 27% higher when losses were taken into account, assuming that 50% of the time the sampled NH4NO3 was exposed to low velocity phase evaporating conditions. Changing atmospheric conditions during sampling can easily lead to this magnitude of losses. Cl also endure evaporation losses though induced by HNO3.
Consequences for the working range. NO3: no practical working range can be defined as it is dependent on the input concentrations of NH3 and HNO3. NH4: no practical working range can be defined as the NH4NO3 part is dependent on the concentrations of NH3 and HNO3. Cl: no practical working range can be defined as Cl is dependent on the concentration HNO3. SO4, Na, K, Ca and Mg: working range is not dependent on sampling conditions and determined by the results of the field test study (WP4).
Performance of the various filter analysis methods applied by the participating laboratories were assessed by Round Robin standard solutions (provided by EMEP) and the field validation tests (WP3). The results are not available yet and will be presented in the statistical analysis report of WP4.
Concern was raised with respect to the homogeneous filter loading during the field trials. This was of importance because filter punches were analyzed by the participating laboratories. The homogeneity was tested by having one lab analyzing the total set of punches coming from two different field trial filters. For all components the relative standard deviation was less or equal to the analytical uncertainty. It was therefore concluded that inhomogeneity of filter loadings as applied at the field validation tests was not detectable.
The European standard for PM accepts the variability of the evaporation losses by convention. This rules out the sampling effects and as a consequence lets the working range of the method be dominated by the analysis uncertainties. According to the definition of PM2.5 for the purpose of the European Standard working range for the ions follows the working range of EN12341 and be restricted by the analytical results presented in statistical analysis report of WP4. Taking the conclusion of this laboratory tests into account the method will not be suited for the objectives (to support air quality assessment and management) of the standard. Results for NH4, NO3 and Cl should be considered as indicative. In order to determine the PM ions quantatively and meet the objectives of the standard denuder filter pack methods or on line analyzers as MARGA should be applied.
Equivalence with the EMEP method was conducted at the participating EMEP field sites (Ispra, Waldhof and Cabauw). EMEP made a standard EMEP sampler available for these sites. Results are to be presented in the statistical analysis report of WP4 as not all analysis results were available by the time this report was submitted.
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