A second look at the Palmes' diffusive sampler.

Area of Science:

• Environmental Science
• Analytical Chemistry
• Air Quality Monitoring

Background:

• The Palmes' tube is a widely used diffusive sampler for gaseous pollutants.
• Previous studies have raised questions about the accuracy of Palmes' tube samplers.
• The theoretical calculations for Palmes' tube accuracy may be insufficient.

Purpose of the Study:

• To measure the mass transfer resistance in a Palmes' diffusive sampler.
• To determine the accuracy of Palmes' tube samplers under varying conditions.
• To assess the need for calibration of Palmes' tube samplers.

Main Methods:

• Measured mass transfer resistance using cyclohexane loss from a Palmes' tube.
• Tested factorial combinations of air incidence angles (270-90 degrees).
• Tested factorial combinations of air speeds (0.5-2.5 m/sec).

Main Results:

• Observed loss rates were 46% to 121% higher than theoretically calculated rates.
• Mass transfer resistance was nearly constant with perpendicular airflow at sufficient speeds.
• Significant deviations indicate theoretical calculations are unreliable.

Conclusions:

• Palmes' tube samplers require calibration due to discrepancies between measured and theoretical rates.
• The widespread acceptance of Palmes' tube results may stem from consistent performance under perpendicular airflow.
• Accurate air quality monitoring necessitates empirical calibration of diffusive samplers.