Prediction of gas/particle partitioning of polybrominated diphenyl ethers (PBDEs) in global air: A theoretical study

Abstract

Gas/particle (G/P) partitioning of semi-volatile organic compounds (SVOCs) is an important process that primarily governs their atmospheric fate, long-range atmospheric transport, and their routes of entering the human body. All previous studies on this issue are hypothetically based on equilibrium conditions, the results of which do not predict results from monitoring studies well in most cases. In this study, a steady-state model instead of an equilibrium-state model for the investigation of the G/P partitioning behavior of polybrominated diphenyl ethers (PB-DEs) was established, and an equation for calculating the partition coefficients under steady state (K PS ) of PBDEs (log K PS = log K PE + logα) was developed in which an equilibrium term (log K PE = log K OA + logf OM −11.91 where f OM is organic matter content of the particles) and a nonequilibrium term (log α, caused by dry and wet depositions of particles), both being functions of log K OA (octanol-air partition coefficient), are included. It was found that the equilibrium is a special case of steady state when the nonequilibrium term equals zero. A criterion to classify the equilibrium and non-equilibrium status of PBDEs was also established using two threshold values of log K OA , log K OA1 , and log K OA2 , which divide the range of log K OA into three domains: equilibrium, non-equilibrium, and maximum partition domain. Accordingly, two threshold values of temperature t, t TH1 when log K OA = log K OA1 and t TH2 when log K OA = log K OA2 , were identified, which divide the range of temperature also into the same three domains for each PBDE congener. We predicted the existence of the maximum partition domain (the values of log K PS reach a maximum constant of −1.53) that every PBDE congener can reach when log K OA ≥ log K OA2 , or t ≤ t TH2 . The novel equation developed in this study was applied to predict the G/P partition coefficients of PBDEs for our Chinese persistent organic pollutants (POPs) Soil and Air Monitoring Program, Phase 2 (China-SAMP-II) program and other monitoring programs worldwide, including in Asia, Europe, North America, and the Arctic, and the results matched well with all the monitoring data, except those obtained at e-waste sites due to the unpredictable PBDE emissions at these sites. This study provided evidence that the newly developed steady-state-based equation is superior to the equilibrium-state-based equation that has been used in describing the G/P partitioning behavior over decades. We suggest that the investigation on G/P partitioning behavior for PBDEs should be based on steady state, not equilibrium state, and equilibrium is just a special case of steady state when non-equilibrium factors can be ignored. We also believe that our new equation provides a useful tool for environmental scientists in both monitoring and modeling research on G/P partitioning of PBDEs and can be extended to predict G/P partitioning behavior for other SVOCs as well.

Are atmospheric PBDE levels declining in central Europe? Examination of the seasonal and semi-long-term variations, gas–particle partitioning and implications for long-range atmospheric transport

“…99, 100, 153, 154, 183 and 209) were negatively correlated with the precipitation rate. This confirms the significant washout of congeners' partitioning mostly to the particulate phase compared to those in the gas phase (Venier and Hites, 2008), a general trend for lipophilic organic compounds (Ligocki et al, 1985;Shahpoury et al, 2015). The atmospheric boundary layer (ABL) height shows strong correlations with the particulate concentrations of all PBDEs except BDE85, in agreement with a previous study (Dien et al, 2017).…”

Three-year monitoring of atmospheric PCBs and PBDEs at the Chinese Great Wall Station, West Antarctica: Levels, chiral signature, environmental behaviors and source implication

“…It was noteworthy that a parameter C ¼ 10 was assumed during calculation, which was higher than the default value used in the study by Li et al (2015). A higher value of C was recommended when high wind speed occurred, such as C ¼ 50 was assumed at Waliguan where the annual average wind speed reached 4.6 m s À1 (Li et al, 2015).…”

“…Recently, Li and Jia (2014) developed a steady-state model to predict the G/P partitioning behavior of PBDEs in air, and the empirical predicted log K PP was expressed as a function of log K OA . Li et al (2015) further developed a theoretical equation (log K PS ), which was considered superior to the equilibrium-state-based equation and successfully applied in some cases. The further details about these two equations are given in SM.…”

“…It was argued that newly released particles at the rural sites caused nonequilibrium partitioning at those sites for PCBs (Lohmann et al, 2000). The non-equilibrium term (log a) could not be a positive number (see the physical meaning of a in Li et al (2015)), thus, the log K PS values would not be higher than the log K PE values at the same log K OA . That is, the steady-state-based equation cannot perform well for lighter PCBs.…”

Spatial–temporal variations, possible sources and soil–air exchange of polychlorinated biphenyls in urban environments in China

“…[46][47][48] The concentrations of PCBs in the corresponding environmental medium and their physicochemical properties, soil properties, and gas-particle partitioning in air are generally regarded as signicant factors that affect their exchange process between the air and soil. [49][50][51] Particularly, the temperature-controlled air-surface exchange was explored, 52 and the fugacity fractions (ff) of the soil-air exchange were calculated by the fugacity approach to investigate the major sources of atmospheric PCBs and the status of PCBs in air and soil in the current environment. There was very little information available on PCB distribution in urban soil in the 11 cities for 2004 and 2008 and the current year.…”