Environmental Monitoring of Low Level Sulphur in Ambient Air

Significance of Monitoring Sulphur in Ambient Air

Monitoring trace levels of sulphur compounds in ambient air is critical for assessing environmental and human health risks. Sulphur species such as carbon disulphide and various mercaptans are indicators of industrial emissions, sewage treatment plant operation and landfill off-gassing. Sensitive, reliable detection at sub-nmol/mol levels enables regulators and industry to respond promptly to potential hazards and to ensure compliance with air quality standards.

Objectives and Study Overview

This study demonstrates a rapid, high-sensitivity method for quantifying eight volatile sulphur compounds in ambient air. Key goals included:

• Developing a thermal desorption–GC method with pulsed flame photometric detection (PFPD).
• Achieving sub-nmol/mol detection limits.
• Validating linearity, repeatability and overall robustness for routine environmental monitoring.

Used Instrumentation

The analytical system comprised:

• Thermal Desorption Unit with cryogenic pre-concentration and programmable temperature ramping.
• Scion GC-456 Gas Chromatograph equipped with a Pulsed Flame Photometric Detector (PFPD).
• Ultra-clean stainless steel valves for standard gas dilution and sample introduction.

Methodology

Ambient air standards were prepared at concentrations of 0.5, 1.0, 2.0, 5.0 and 8.0 nmol/mol. Thermal desorption conditions included a cold trap at –10 °C, followed by a rapid heat ramp to 300 °C. GC separation employed a 30 m GASPRO column with an oven temperature program from 80 °C to 260 °C. The PFPD was operated at 250 °C with optimized gas flows.

Results and Discussion

Repeatability testing at 5.0 nmol/mol showed eight consecutive injections with well-resolved peaks for all sulphur analytes. Calibration curves exhibited exceptional linearity (R² ≥ 0.9999), with most compounds achieving an R² of 1. Method Detection Limits (MDLs) at the 0.5 nmol/mol level ranged from 0.06 to 0.10 nmol/mol. Relative standard deviations (RSDs) across eight replicates were below 3% for all targets, highlighting the method’s precision.

Practical Benefits and Applications

The validated method delivers rapid turnaround (<15 minutes per run), high sensitivity and robust performance. It is ideally suited for:

• Regulatory compliance monitoring near industrial sites.
• Continuous ambient air surveillance in urban or rural settings.
• Process control at wastewater treatment and landfill facilities.

Future Trends and Opportunities

Advances in micro-GC technology and detector miniaturization may further reduce analysis time and field deployment costs. Integration with real-time data networks and automated sampling platforms promises continuous, high-resolution mapping of sulphur emissions. Emerging detectors with enhanced selectivity could expand the analyte scope to include oxygenated sulphur species.

Conclusion

The combination of thermal desorption GC and PFPD provides a fast, reliable solution for low-level sulphur monitoring in ambient air. Outstanding linearity, low detection limits and excellent repeatability confirm its suitability for both routine environmental surveillance and targeted emission studies.