In:
Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 12, No. 6 ( 2019-06-13), p. 3137-3149
Abstract:
Abstract. Recent work has quantified the delay times in measurements of volatile
organic compounds (VOCs) caused by the partitioning between the gas phase
and the surfaces of the inlet tubing and instrument itself. In this study we
quantify wall partitioning effects on time responses and transmission of
multifunctional, semivolatile, and intermediate-volatility organic compounds
(S/IVOCs) with saturation concentrations (C∗) between 100 and 104 µg m−3. The instrument delays of several chemical ionization
mass spectrometer (CIMS) instruments increase with decreasing C∗, ranging from
seconds to tens of minutes, except for the NO3- CIMS where it is
always on the order of seconds. Six different tubing materials were tested.
Teflon, including PFA, FEP, and conductive PFA, performs better than metals
and Nafion in terms of both delay time and transmission efficiency.
Analogous to instrument responses, tubing delays increase as C∗ decreases,
from less than a minute to 〉100 min. The delays caused by Teflon
tubing vs. C∗ can be modeled using the simple chromatography model of Pagonis
et al. (2017). The model can be used to estimate the equivalent absorbing
mass concentration (Cw) of each material, and to estimate delays under
different flow rates and tubing dimensions. We also include time delay
measurements from a series of small polar organic and inorganic analytes in
PFA tubing measured by CIMS. Small polar molecules behave differently than
larger organic ones, with their delays being predicted by their Henry's law
constants instead of their C∗, suggesting the dominance of partitioning to
small amounts of water on sampling surfaces as a result of their polarity
and acidity properties. PFA tubing has the best performance for gas-only
sampling, while conductive PFA appears very promising for sampling S/IVOCs
and particles simultaneously. The observed delays and low transmission both
affect the quality of gas quantification, especially when no direct
calibration is available. Improvements in sampling and instrument response
are needed for fast atmospheric measurements of a wide range of S/IVOCs
(e.g., by aircraft or for eddy covariance). These methods and results are
also useful for more general characterization of surface–gas interactions.
Type of Medium:
Online Resource
ISSN:
1867-8548
DOI:
10.5194/amt-12-3137-2019
DOI:
10.5194/amt-12-3137-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2505596-3