Sampling efficiency of flow-through air sampler: Effect of sampling rate

Abstract

The Flow Through Sampler (FTS) serves as an efficient wind-powered active sampling device, enabling the collection of a significant air volume within a short duration. Throughout the actual sampling process, the sampling rate of FTS experiences continuous fluctuations, highlighting the need for in-depth investigation into its impact on breakthrough. In this study, we interconnected the FTS sampling column with three distinct pumps, operating at five varied sampling rates under 293 K and 303 K; and breakthrough profiles of PCBs, PAHs and OCPs on the FTS sampling column were investigated to understand the impacts of sampling rate, expressed as linear wind velocity through the cross section of FTS tube (u) on the sampling efficiency of the sampling column. It revealed that the number of theoretical plates (N) and the logarithm of breakthrough volume (logV_B) of compounds on the FTS-PUF column exhibit linear relationships with the inverse of wind velocity (1/u). The slopes of the fitted lines (K_Nu) are closely associated with the volatility of the compounds. Compounds with volatility experience a greater impact from variations in wind velocity on their N value on the sampling column. The effect on the most volatile PCBs surpasses that of PAHs and OCPs. Moreover, the slopes of logV_B for different compounds affected by wind speed (K_VB-u), display a significant correlation with compound volatility (logP_L). Wind speed exerts a stronger influence on the breakthrough volume of low volatile compounds compared to volatile compounds. Multiple linear regression and LSER analysis further confirms a significant positive correlation between N and logV_B across different temperatures and wind velocities (log(V_B/m³)=2010/(T/K)-0.00066/(u/(m/s))+0.55N-5.41, R²=0.83, n = 423, p = 0). Therefore, the collection performance of the FTS-PUF sampling column for all types of compounds can be predicted under varying temperatures and wind velocitiess/sampling rates. Given the known sampled air volume, the breakthrough level for any chemicals can be estimated, which provids valuable data support for accurate monitoring of atmospheric organic pollutant concentrations.