Unique calibration of passive air sampling for field monitoring of PAHs with polyethylene thin films across seasons and locations

Abstract

Although passive sampling has been applied to determine concentrations of semi-volatile organic chemicals such as polycyclic aromatic hydrocarbons (PAHs) in air and water for about two decades and is well established, several uncertainties and challenges remain. This study presents a comprehensive validation of polyethylene thin sheets as passive air samplers (PE-PAS), detailing alternative approaches to calibration and analysis. Besides measuring the uptake kinetics in the field using time series deployments of PE-PAS at 3 field sites under varying seasonal conditions (temperature, wind) with a performance reference compound (PRC), we implement a numerical model to fit uptake kinetics based on partition and diffusion coefficients adapted to hourly changes of temperature. This model follows similar approaches as reported in earlier studies, but we use loss curves of a spiked PRC (anthracene-D₁₀) to fit the air-side boundary layer (δ_g), which is limiting mass transfer between air and PE, instead of calibrating the PAS sampling rate. Surprisingly, air side boundary layers, and thus inherent sampling rates, were almost equal at the different locations but varied for the different sampling campaigns by about a factor of two. This variation is probably due to short term effects, but a robust average over all seasons and locations could be obtained (1 mm ± 0.5 mm) which is characteristic for our sampling design. A well-known δ_g allows concentrations in air of compounds with very different uptake kinetics onto the PE-PAS to be estimated. Additionally, as in previous studies, our results indicate stable distribution patterns of PAHs in the environment of the study region in Germany. Given a practical chosen PE-PAS deployment time, representative compounds may be selected that integrate over the desired monitoring time period (e.g. fluorene for days, phenanthrene for weeks and pyrene or fluoranthene for many months to years). Measurement of one PAH applied with specific ratios derived from stable distribution patterns of PAHs, in the absence of influential local point sources, can then be used to estimate air concentrations of PAHs that are more difficult to quantify during the monitoring period.