Quantitative passive soil vapor sampling for VOCs--Part 4: Flow-through cell

Area of Science:

• Environmental Science
• Analytical Chemistry
• Geochemistry

Background:

• Conventional active sampling of volatile organic compounds (VOCs) in soil gas requires precise flow rate control, which is challenging due to variable subsurface material permeability.
• Passive sampling offers a potentially simpler alternative by reducing the need for exact flow rate measurements.

Purpose of the Study:

• To compare the performance of several quantitative passive samplers for monitoring VOCs in soil gas using a flow-through cell.
• To evaluate the influence of flow rate and sampling duration on passive sampler accuracy.

Main Methods:

• A controlled experiment utilized a 500 mL flow-through cell with a fractional factorial design.
• Tested five different passive samplers (ATD Tube, Radiello®, SKC Ultra, Waterloo Membrane Sampler™, 3M™ OVM 3500) at varying flow rates (80, 670, 930 mL/min) and durations (10, 15, 20 min).
• Compared passive sampler results against a baseline from Summa canister analyses using EPA Method TO-15.

Main Results:

• Passive sampler concentrations were within a factor of 2 of Summa canister concentrations in 32 out of 35 cases.
• Low flow rates and short durations resulted in underestimated VOC concentrations, likely due to insufficient cell purging.

Conclusions:

• Quantitative passive samplers are a viable and simpler alternative to active sampling for soil gas VOC monitoring.
• Sufficient flow rate and sampling duration are critical for accurate passive sampling to ensure adequate cell purging and avoid underestimation.