ECN publication
The continuous analysis of nitrate and ammonium in aerosols by the Stream Jet Aerosol Collector (SJAC) : extension and validation of the methodology
Published by: Publication date:
ECN 1-11-2000
ECN report number: Document type:
ECN-RX--00-039 Other
Number of pages: Full text:
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Classical methodology based on the application of filters for sampling, followed by extraction and analysis, introduces severe artifacts for semi-volatile compounds like ammonium nitrate. These filter methods do not meet the requirements for the assessment of the impact of aerosols on acidification, air quality and especially on the radiative balance, in terms-of required speed, detection limits and selectivity. These artifacts are avoided by using a Steam Jet Aerosol Collector (SJAC) sampler, based on scavenging of aerosols by droplet formation, in combination with on-line analytical techniques such as Ion-Chromatography for nitrate and membrane separation followed by conductivity detection for ammonium. The SJAC sampler combines very low blanks with high efficiency of collection of particles. The ammonium detector and the IC system, based on 1 point internal standard calibration in combination with correction for curved calibration graphs, enables detection of ammonium and nitrate at background conditions, the detection limit is about 0.02 mug.m-3 of ammonium and nitrate. Accuracy is, depending on ambient concentration, in the order of 5 to 10 % relative, at a range of 0.05 to 50 mu g-3. The time resolution is 15 to 120 minutes, depending on required detection limit, and is short enough for continuously monitoring the chemical composition of aerosols. Quality Assurance and Quality Control experiments and intercomparison experiments with classical filter methods, thermo-denuder systems, denuder difference methods and other continuous monitoring techniques have shown that the results are reliable. The instrument has successfully been employed in field campaigns in Europe and the US. 13 refs.

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