Improvements to Ambient Air Monitoring (U.S. EPA PAMS) Using a Clarus 690 Gas Chromatograph

Importance of Topic

Monitoring volatile organic compounds (VOCs) that form ground-level ozone is critical for protecting public health and ensuring compliance with air quality standards. On-line analysis reduces sample loss and enables timely correlation with meteorological data. Improvements in gas chromatographic separation and sampling robustness are essential for accurate ambient air monitoring.

Objectives and Study Overview

This study presents enhancements to the Photochemical Assessment Monitoring Stations (PAMS) methodology by optimizing chromatographic separation, trap design and system automation. Key aims included:

• Replacing the BP-1 column with an Elite-624Sil MS column for improved resolution of C2–C12 VOCs
• Implementing a modern Swafer-based Dean Switch to simplify heart-cutting operations
• Developing an enhanced three-bed sorbent trap with guard zone to reduce background contamination

Methodology

An on-line system coupled a TurboMatrix thermal desorber with a dual-column GC (Clarus 590/690) and wide-range flame ionization detectors. Samples were drawn for 40 minutes each hour, cryogen-free trapping at –30 °C, followed by thermal desorption and separation under a temperature program from 45 °C to 200 °C. Retention time stability and precision were evaluated under varying humidity conditions using dynamic dilution of calibration gas mixtures.

Instrumentation Used

• Clarus 590/690 gas chromatograph with Swafer heart-cutting device
• Elite-624Sil MS primary column, 60 m × 0.25 mm
• TurboMatrix™ thermal desorber with on-line sampling accessory
• Dual wide-range flame ionization detectors
• Custom dynamic dilution system for PAMS and TCEQ calibration mixtures

Main Results and Discussion

The Elite-624Sil MS column delivered sharper peaks and fewer co-elutions than the BP-1 phase, enabling reliable quantification of over 60 target compounds. Retention times showed relative standard deviations below 0.07 % over 30 runs at high humidity. Method detection limits remained under 0.1 ppb as ppbc across humidity ranges. Linear retention indices confirmed consistent compound identification.

Benefits and Practical Applications

• Unattended, hourly sampling meets stringent PAMS and TCEQ requirements
• Cryogen-free operation simplifies field deployment
• Improved trap design reduces carryover of non-target compounds
• Automated calibration and remote control enhance reliability and reduce maintenance

Future Trends and Potential Applications

Advances in sorbent materials and detector technologies may further lower detection limits and expand target lists. Integration with meteorological networks and real-time data analytics will enable more responsive air quality management. Miniaturized GC systems and alternative detectors could support wider deployment in urban and remote areas.

Conclusion

The optimized on-line ozone precursor analyzer demonstrates robust, high-resolution monitoring of VOCs in ambient air. Upgrades in column selection, trap architecture and automation improve accuracy, precision and operational ease, supporting regulatory compliance and air quality research.

References

1. U.S. Environmental Protection Agency. Technical Assistance Document for Sampling and Analysis of Ozone Precursors, EPA/600-R-98/161, 1998
2. Kotzias D., Duane M., Munari F. Proceedings of the Third International Conference on Air Pollution, Porto Carras, Greece, 1995
3. European Commission. Directive 2002/3/CE on ozone precursor compounds, 2002
4. U.S. Environmental Protection Agency. Revised Photochemical Assessment Monitoring Stations Target List, 2017
5. PerkinElmer. A Study of Performance in Low and High Humidity Environments, Application Note, 2018