| dc.description.abstract |
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 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 5-10\% relative, at a range of 0.05-50 mug m(-3). The:
time resolution is 15-120min, 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. (C) 2001 Elsevier Science Ltd.
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