Atmospheric Monitoring of Volatile Organic Compounds Using Programmed Temperature Vaporization Injection

Importance of the topic

Atmospheric volatile organic compounds (VOCs) play a critical role in urban and rural air quality, human health risks, and photochemical processes leading to ozone and secondary pollutant formation. Accurate, sensitive, and continuous monitoring of C2–C6 and C5–ClO VOCs is essential for source apportionment, regulatory compliance, and modeling of tropospheric chemistry.

Objectives and Study Overview

This study aimed to develop and validate an automated, cryogen‐free method for near‐real‐time determination of C2–C6 and C5–ClO VOCs in both urban and biogenic emission environments. The approach employs programmed temperature vaporization (PTV) injection directly from an activated charcoal sorbent tube, eliminating intermediate cryogenic refocusing and enabling high‐throughput hourly analysis.

Applied Methodology and Instrumentation

Air samples (typically 600 mL) were drawn through an activated charcoal sorbent tube at 60 mL min⁻¹, with the trap cooled to –10 °C by CO₂ and PTV‐controlled flow. After sampling, carrier gas purged the trap, then rapid PTV heating (–10 °C to 400 °C at 16 °C s⁻¹) transferred analytes onto the analytical column. Two column configurations were used:

• C5–ClO analysis: 60 m × 0.53 mm i.d. dimethyl polysiloxane (RTX-1) column.
• C2–C6 analysis: 50 m × 0.53 mm i.d. Al₂O₃ PLOT column (doped with Na₂SO₄).

Detection employed a flame ionization detector (FID) with generated zero air and hydrogen. High helium flow (20 mL min⁻¹) expedited trap cleaning, enabling continuous, unattended operation.

Main Results and Discussion

Breakthrough experiments established safe sample volumes up to 600–1 000 mL for most VOCs. Urban air analysis yielded detection limits of 50–100 ppt for 38 C5–ClO species, with hourly monitoring feasible. In a rural Sitka spruce forest study, C2–C6 species including isoprene were detected down to 50–70 ppt; isoprene concentrations reached up to 1.2 ppb in ambient samples. The absence of intermediate cryogenic refocusing did not compromise peak resolution, and the upstream trap was effectively regenerated between runs.

Benefits and Practical Applications of the Method

The automated PTV‐sorbent tube approach offers:

• Elimination of liquid nitrogen or dry‐ice coolants.
• Rapid cycle times enabling hourly resolution.
• Reduced maintenance and consistent tube reuse.
• Suitability for mobile or remote field laboratories.

These advantages support urban air quality networks and in situ biogenic emission studies without requiring sample transport or cryogen supply.

Future Trends and Potential Applications

Advances may include alternative sorbents (e.g., Tenax TA) for extended compound range, integration with mass spectrometric detectors for structural confirmation, and deployment on fixed networks or UAV platforms. Further miniaturization and software automation could enable real‐time spatial mapping of VOC distributions in urban street canyons and forest canopies.

Conclusion

The PTV‐sorbent tube GC‐FID method provides a sensitive, robust, and cryogen‐free solution for continuous atmospheric VOC monitoring. Its streamlined design and high throughput make it well suited for both regulatory networks and research applications in diverse environments.

Applied Instrumentation

• Activated charcoal sorbent tube (30–60 mesh, coconut charcoal).
• OPTIC 400 PTV injector (Ai Cambridge).
• Wide‐bore RTX-1 and Al₂O₃ PLOT GC columns (0.53 mm i.d.).
• Gas chromatograph (Carlo-Erba GC8000) with FID.
• Zero‐air and H₂ generators (Packard Instruments).
• Pneumatic six‐port valves (Valco).

Reference

[1] Sweet CW, Vermette SJ. Environ Sci Technol. 1992;26:165.
[2] Hadley RA, Cass GR. Environ Sci Technol. 1994;28:88.
[3] EPAQS. Benzene. HM Stationery Office; 1993.
[4] PORG. Ozone in the United Kingdom. Dept. Environment; 1993.
[5] Jenkin ME, et al. Tropospheric Chemistry Modelling. AEA report; 1995.
[6] O’Doherty SJ, et al. J Chromatogr. 1993;630:264.
[7] Ciccoli C, et al. J High Resol Chromatogr. 1992;15:75.
[8] Kruschel BD, et al. J High Resol Chromatogr. 1994;17:187.
[9] Montzka SA, et al. J Geophys Res. 1993;98:1101.
[10] Mattinen ML, Maria O. Proc 14th Int Symp Cap Chromatogr. 1992:307.
[11] Woolfenden EA, et al. Proc Int Conf VOC Environ. 1993:321.
[12] Derwent J, et al. AEA Technology Report; 1994.
[13] Denha AM, Bartle KD, Pilling MJ. Anal Proc. 1994;31:297.
[14] Lewis AC, et al. Atmos Environ. 1995;29:1871.
[15] Camel B, Caude M. J Chromatogr. 1995;710:3.
[16] Brown RH, Purnell CJ. J Chromatogr. 1979;178:79.
[17] Grosjean D, et al. Environ Sci Technol. 1993;27:830.
[18] Martin RS, et al. J Atmos Chem. 1991;13:1.
[19] Fehsenfeld FC, et al. Glob Biogeochem Cycles. 1992;6:389.
[20] Kruschel BD, et al. J High Resol Chromatogr. 1994;17:187.