 |
| Titel |
On transport phenomena and equilibration time scales in thermodenuders |
| VerfasserIn |
R. Saleh, A. Shihadeh, A. Khlystov |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1867-1381
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 3 ; Nr. 4, no. 3 (2011-03-18), S.571-581 |
| Datensatznummer |
250001804
|
| Publikation (Nr.) |
 copernicus.org/amt-4-571-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| This paper presents a theoretical and experimental investigation of
thermodenuders that addresses two controversial issues: (1) equilibration time
scales and (2) the need for an activated carbon (AC) denuder in the cooling
section. We describe a plug flow model for transport phenomena in a TD, which
can be used to simulate the rate of vapor build-up in the gas phase and the
corresponding change in particle size distribution. Model simulations were
found to have excellent agreement with experiments performed with pure and
mixed dicarboxylic acid aerosols. Both simulations and experiments showed
that the aerosols approached equilibrium within reasonable residence times
(15 s–30 s) for aerosol concentrations and size distributions typical for
laboratory measurements, and that volatility studies at sufficiently high
aerosol loadings, therefore, need not resort to kinetic models for inference
of thermodynamic properties. However, for size distributions relevant for
ambient aerosols, equilibration time scales were much larger than residence
times available with current TD designs. We have also performed dimensional
analysis on the problem of equilibration in TDs, and derived a dimensionless
equilibration parameter which can be used to determine the residence time
needed for an aerosol of given size distribution and kinetic properties to
approach equilibrium. It is also shown theoretically and empirically that
aerosol volatility has no effect on the equilibration time scales. Model
simulations and experiments showed that with aerosol size distributions
relevant to both ambient and laboratory measurements re-condensation in the
cooling section, with and without an AC denuder, was negligible. Thus, there
is no significant benefit in using an AC denuder in the cooling section. Due
to the risk of stripping volatile material from the aerosol, the use of AC
denuders in the cooling section should be avoided. Finally, we present a
rationale for why ΔC is the proper measure of volatility, while
using mass fraction remaining (MFR) can be misleading. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|