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| Titel |
Results of the first air ion spectrometer calibration and intercomparison workshop |
| VerfasserIn |
E. Asmi, M. Sipilä, H. E. Manninen, J. Vanhanen, K. Lehtipalo, S. Gagné, K. Neitola, A. Mirme, S. Mirme, E. Tamm, J. Uin, K. Komsaare, M. Attoui, M. Kulmala  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 1 ; Nr. 9, no. 1 (2009-01-09), S.141-154 |
| Datensatznummer |
250006635
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| Publikation (Nr.) |
 copernicus.org/acp-9-141-2009.pdf |
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| Zusammenfassung |
| The Air Ion Spectrometer (AIS) measures mobility and size distributions of
atmospheric ions. The Neutral cluster and Air Ion Spectrometer (NAIS) can
additionally measure neutral particles. The number of the (N)AIS instruments
in the world is only 11. Nevertheless, they are already widely used in
atmospheric ion studies, particularly related to the initial steps of new
particle formation. There is no standard method applicable for calibrating
the ion spectrometers in the sub-3 nm ion range. However, recent development
of high resolution DMAs has enabled the size separation of small ions with
good mobility resolution. For the first time, the ion spectrometers were
intercompared and calibrated in a workshop, held in January–February 2008 in
Helsinki, Finland. The overall goal was to experimentally determine the
(N)AIS transfer functions. Monomobile mobility standards, 241-Am charger ions
and silver particles were generated and used as calibration aerosols. High
resolution DMAs were used to size-separate the smaller (1–10 nm) ions,
while at bigger diameters (4–40 nm) the size was selected with a HAUKE-type
DMA. Negative ion mobilities were detected by (N)AISs with slightly better
accuracy than positive, nonetheless, both were somewhat overestimated. A
linear fit of slope of one to the whole dataset of mobilities suggested that
(N)AISs measured the negative mobilities 1.36±0.16 times larger compared
with the reference instruments. Similarly, positive mobilities were measured
1.39±0.15 times larger compared with the reference instruments. The
completely monomobile mobility standards were measured with the best
accuracy. The (N)AIS concentrations were compared with an aerosol
electrometer (AE) and a condensation particle counter (CPC). At sizes below
1.5 nm (positive) and 3 nm (negative) the ion spectrometers detected higher
concentrations while at bigger sizes they showed similar concentrations as
the reference instruments. The total particle concentrations measured by the
NAISs were within ±50% of the reference CPC concentration at 4–40 nm
sizes. The lowest cut-off size of the NAIS in neutral particle measurements
was determined to be between 1.5 and 3 nm, depending on the measurement
conditions and the polarity. |
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