Diurnal Variations of Air-Soil Exchange of Semivolatile Organic Compounds (PAHs, PCBs, OCPs, and PBDEs) in a Central European Receptor Area

Abstract

Concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs) in air and soil, their fugacities, and the experimental soil-air partitioning coefficient (KSA) were determined at two background sites in the Gt. Hungarian Plain in August 2013. The concentrations of the semivolatile organic compounds (SOCs) in the soil were not correlated with the organic carbon content but with two indirect parameters of mineralization and aromaticity, suggesting that soil organic matter quality is an important parameter affecting the sorption of SOCs onto soils. Predictions based on the assumption that absorption is the dominant process were in good agreement with the measurements for PAHs, OCPs, and the low chlorinated PCBs. In general, soils were found to be a source of PAHs, high chlorinated PCBs, the majority of OCPs and PBDEs, and a sink for the low chlorinated PCBs and γ-hexachlorocyclohexane. Diurnal variations in the direction of the soil-air exchange were found for two compounds (i.e., pentachlorobenzene and p,p'-dichlorodiphenyldichloroethane), with volatilization during the day and deposition in the night. The concentrations of most SOCs in the near-ground atmosphere were dominated by revolatilization from the soil.

Assessing soil-air partitioning of PAHs and PCBs with a new fugacity passive sampler

“…Uncertainty of f ratio was estimated at 45% after incorporating all error ranges in air concentrations, soil air concentrations, and log K oa (Harner et al, 2001; Wang et al, 2016); more details are provided in SI. This range of uncertainty is similar to previous reports measuring soil-air partitioning: 43% (Degrendele et al, 2016) and 30–40% (Liu et al, 2016). In this work, values of f ratio outside 0.55—1.45 (log 10 f ratio : −0.26—0.19) indicate significant deviations from equilibrium (SI).…”

“…Wang et al (2014) found that low-molecular weight PAHs were volatilizing, and high-molecular weight PAHs were depositing to soil on “pristine” pastureland of the Tibetan Plateau. In contrast, Degrendele et al (2016) measured numerous semivolatile contaminants at background sites in Hungary, and found that the more volatile, less-chlorinated PCB congeners were depositing, while the heavier, less-volatile PCBs were volatilizing. Similarly, our data suggest that the most-volatile, lightweight compounds were either depositing or were at equilibrium during our study period.…”

“…The unitless fugacity ratio ( f ratio ) indicates the net direction of exchange of a compound between the air and soil surface (Cabrerizo et al, 2009; Degrendele et al, 2016; Harner et al, 2001; McDonough et al, 2016; Wang et al, 2014; Wang et al, 2015): $$f_{\mathrm{italicratio}}=\frac{f_{\mathit{soil}\mathit{air}}}{f_{\mathrm{italicair}}}$$ where f ratio > 1 indicates volatilization out of the soil and f ratio < 1 indicates deposition.…”

“…Fugacity of soil air ( f soil air , atm) and air ( f air , atm) are calculated using the same equation: $$f_{(\mathit{soil})\mathit{air}}=\frac{C_{false(\mathrm{italicsoil}false)\mathrm{italicair}}RT}{MW\ast {10}^{15}}$$ where C (soil)air (ng m −3 ) is the concentration of analyte in soi) is the concentrat 3 atm K −1 mol −1 ) is the gas constant, T (K) is the temperature measured within soil air or air box, MW (g mol −1 ) is molecular weight of the analyte, and 10 15 is a unit conversion factor (Cabrerizo et al, 2009; Degrendele et al, 2016; Wang et al, 2015). Alternatively, Eq.…”

Modeling short-term concentration fluctuations of semi-volatile pollutants in the soil–plant–atmosphere system

“…These factors are highly specific to site location, composition of microbial and plant communities, plant coverage as well as solar radiation. For instance, based on the results of two different studies in which the same methods at uncultivated grassland sites were applied, the authors hypothesized that a biogenic source cause steep soil-atmosphere gradients of some PAHs in temperate locations in Spain and England (Cabrerizo et al, 2011), but not in Hungary (Degrendele et al, 2016). It is known that perylene and possibly phenanthrene, for example, may be produced by the activity of termites in tropical soils (Wilcke et al, 2002), or microbial reactions under anaerobic conditions (Venkatesan, 1988;Wilcke et al, 1999), but the importance of this in temperate, unsaturated soils is unclear.…”