Effects of gas–wall partitioning in Teflon tubing and instrumentation on time-resolved measurements of gas-phase organic compounds

Abstract

Abstract. Recent studies have demonstrated that organic compounds can partition from the gas phase to the walls in Teflon environmental chambers and that the process can be modeled as absorptive partitioning. Here these studies were extended to investigate gas-wall partitioning of organic compounds in Teflon tubing and inside a protontransfer-reaction mass spectrometer (PTR-MS) used to monitor compound concentrations. Rapid partitioning of C 8 -C 14 2-ketones and C 11 -C 16 1-alkenes was observed for compounds with saturation concentrations (c * ) in the range of 3 × 10 4 to 1 × 10 7 µg m −3 , causing delays in instrument response to step-function changes in the concentration of compounds being measured. These delays vary proportionally with tubing length and diameter and inversely with flow rate and c * . The gas-wall partitioning process that occurs in tubing is similar to what occurs in a gas chromatography column, and the measured delay times (analogous to retention times) were accurately described using a linear chromatography model where the walls were treated as an equivalent absorbing mass that is consistent with values determined for Teflon environmental chambers. The effect of PTR-MS surfaces on delay times was also quantified and incorporated into the model. The model predicts delays of an hour or more for semivolatile compounds measured under commonly employed conditions. These results and the model can enable better quantitative design of sampling systems, in particular when fast response is needed, such as for rapid transients, aircraft, or eddy covariance measurements. They may also allow estimation of c * values for unidentified organic compounds detected by mass spectrometry and could be employed to introduce differences in time series of compounds for use with factor analysis methods. Best practices are suggested for sampling organic compounds through Teflon tubing.

Characterizing sources and emissions of volatile organic compounds in a northern California residence using space‐ and time‐resolved measurements

“…As a reference point, the response delay due to the use of 30-meter-long tubes was estimated to be 0.8 minutes for nonanal (C 9 H 18 O) at this flow rate. 33 Two different sampling sequences were employed for gas measurements during observational monitoring. During most periods, data were collected with spatial resolution emphasized, switching regularly at 5-minute intervals among each of the six inlets (ie, 30 minutes for one full cycle).…”

Non-methane organic gas emissions from biomass burning: identification, quantification, and emission factors from PTR-ToF during the FIREX 2016 laboratory experiment

“…3.3.1), inlet losses of highly volatile compounds were negligible, but we were not able to quantify possible losses of less volatile compounds. Measurement of compounds with saturation vapor pressure (C 0 ) less than 10 5 µg m −3 may be affected (Pagonis et al, 2017). A slight delay in the instrument response to some compounds with C 0 close to 10 4 µg m −3 was observed.…”

“…Many more IVOC species have been measured by 2-D-GC (Hatch et al, 2017). It is expected that many species of C 0 < 10 4 µg m −3 were not transmitted through the transfer inlet and instrument tubing quickly enough to be quantifiable by the PTR-MS (Pagonis et al, 2017).…”

No Particle Mass Enhancement from Induced Atmospheric Ageing at a Rural Site in Northern Europe

“…The accommodation coefficient on Teflon is orders of magnitude lower than 0.1 [35,36], but to our knowledge, no literature data on wall accommodation coefficients on stainless steel exist. Pagonis et al [37] investigated the effect of partitioning between gas and Teflon tubing for several VOCs, and found that significant delays due to the retention times could occur. The time-scales for equilibrium partitioning in the inlet is unknown, but the duration of the measurements, together with the PTR-MS measurements, favors the conclusion that the lack of reactor SOA production was not due to VOC losses.…”