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Development and validation of a portable gas phase standard generation and calibration system for volatile organic compounds

Atmospheric Measurement Techniques (2010) 3(3) 683-691
DOI: 10.5194/amt-3-683-2010
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Abstract

We report on the development of an accurate, portable, dynamic calibration system for volatile organic compounds (VOCs). The Mobile Organic Carbon Calibration System (MOCCS) combines the production of gas-phase VOC standards using permeation or diffusion sources with quantitative total organic carbon (TOC) conversion on a palladium surface to CO 2 in the presence of oxygen, and the subsequent CO 2 measurement. MOCCS was validated using three different comparisons: (1) TOC of high accuracy methane standards compared well to expected concentrations (3% relative error), (2) a gas-phase benzene standard was generated using a permeation source and measured by TOC and gas chromatography mass spectrometry (GC-MS) with excellent agreement (<4% relative difference), and (3) total carbon measurement of 4 known gas phase mixtures were performed and compared to a calculated carbon content to agreement within the stated uncertainties of the standards. Measurements from laboratory biomass burning experiments of formic acid by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS) and formaldehyde by proton transfer reaction-mass spectrometry (PTR-MS), both calibrated using MOCCS, were compared to open path Fourier transform infrared spectroscopy (OP-FTIR) to validate the MOCCS calibration and were found to compare well (R 2 of 0•91 and 0•99, respectively). © 2010 Author(s).

Figures

  • Fig. 1. A schematic diagram of the TOC calibration system. Gas standards are selectively passed over a palladium cat ly t (CC). The CO2 generated via oxidation of a standard is then measured using NDIR. During a background measurement, valves 1 and 4 open to allow flow to bypass the catalyst. At this time, valves 2 and 3 are closed shut and valves 5 and 6 are opened to flush the catalyst with zero air. To make a total carbon measurement, valves 2 and 3 opened, 5 and 6 closed, and valves 1 and 4 are switched to allow the sample to flow through the catalyst with the outflow to the CO2 detector.
  • Figure 2. Calibration of the Beckman 870 NDIR CO2 analyzer. Four CO2 gas standards were 3 
  • Fig. 3. CO2 measurements showing two complete cycles of background and TOC measurement of a benzene standard generated by MOCCS, Fig. 3a. The TOC measurements are shown in black with open circles and the background measurements are shown in grey. Subtracting the interpolate ground an d viding the result by the number of carbon atoms in a benzene molecule (6) gives the benzene concentration from the permeation source. After the signal stabilizes, an average of the measured signal minus background is taken (shown as the data between the dashed line). Shown in Fig. 3b are replicate measurements of the benzene concentration made over the course of five days. The average concentration over this time period (38 cycles) was determined to be 13.8± 1.0 ppmv of carbon (ppmvC).
  • Table 1. Standard gas mixtures.
  • Fig. 5. The results of a total carbon analysis of 4 gas phase VOC standards. The con ents of each mixture are detailed in Table 1. An uncertainty of 20% was assumed for each component in the laboratory-generated VOC standards.
  • Fig. 4. Results of MOCCS determined methane concentration compared to GMD determined methane concentration of two standards, Fig. 4a. The relative difference between the two measurements is 3%. The results of GC-MS/TOC measurements of two benzene standards generated using MOCCS, Fig. 4b. The relative difference between the two measurements is less than 4%.
  • Table 2. Performance of MOCCS with the Beckman Industrial Model 870 NDIR and the LI-COR LI-6252.
  • Figure 7. Formic acid measurement comparison using MOCCS with the Beckman model 870 3 

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CITATION STYLE

APA

Veres, P., Gilman, J. B., Roberts, J. M., Kuster, W. C., Warneke, C., Burling, I. R., & De Gouw, J. (2010). Development and validation of a portable gas phase standard generation and calibration system for volatile organic compounds. Atmospheric Measurement Techniques, 3(3), 683–691. https://doi.org/10.5194/amt-3-683-2010

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