Gas/particle Partitioning Steady State Model Theory For Semi-volatile Organic Compounds And Applications

The gas/particle（G/P）partitioning of semi-volatile organic compounds（SVOCs）is extremely important process for their long-range atmospheric transport,wet and dry depositions and fate.Several persistent organic pollutants are belong to SVOCs.These chemicals have been attracting increasing attention for they are toxic,persistent,longdistance transportable,bioaccumulable.However,the predictions of G/P partitioning equilibrium model often do not match the monitoring data,and this deviation can be significant and cannot be ignored under some circumstands.Therefore,a steady state dynamic mass transfer model was set up to investigate the dynamic mass transfer process.The prediction level of G/P partitioning by steady state model was analyzed,and the scientific problems of G/P partitioning theory and long range transport were also solved.The dynamic differential equations of G/P partitioning were derived.Two scenarios were studied to simulate the transition process of SVOCs from initiation of sorption to particles（non-steady state）through the establishment of steady state,and the characteristic time of steady state was analyzed.The equations were applied to polybrominated diphenyl ethers（PBDEs）.The results led to an equilibrium when only the exchange of SVOCs between gas-and particle-phases was considered;however,if both the exchange of SVOCs between gas-and particle-phases and the wet and dry depositions of particles were taken account,the result gave a steady state but not an equilibrium.In addition,SVOCs,where particle deposition occurs,reached a steady nonequilibrium state sooner than they would reach steady equilibrium.The time for SVOCs to reach steady state in the atmosphere is short,most likely within minutes or hours.Present study revealed that G/P partitioning and particle deposition of SVOCs were dependent on each other.The prediction level of G/P partitioning for several SVOCs by steady state model was investigated.The G/P partitioning of PBDEs,organochlorine pesticides（OCPs）,polychlorinated biphenyls（PCBs）,polychlorinated naphthalenes（PCNs）were predicted by the steady state model and verified by the monitoring data.The predictions by five equilibrium models,empirical models,and steady state model as well were compared and verified by the monitoring data.The results revealed that steady state model provid the best agreement to the monitoring data over all the other models when log K_OA > 9.5.The percentages within the ±1 log unit of the results predicted by steady state model for PBDEs,OCPs,PCBs,and PCNs were 94.3%、91.1%、96.1%、92.9%,respectively,higher than those projected by other models.The theoretical prediction formulas of slope m（mo and mp）and intercept b（b_o and b_p）in the logarithmic linear relationship between partition quotient（K_P）and octanol-air partition coefficient(K_OA)and subcooled liquid vapor pressure（P_L）were derived by steady state model.The predicted mo,bo,mp and bp were further compared with monitoring data.It was found that experimental,analytical,or statistical artifacts and other reported factors were not the major parameters for the deviation of slope mp from-1 or mo from 1 for SVOCs.Instead,it was their inherent parameter,K_OA,being the major parameter to determine their values of mo and bo,and equivalently,P_L was the major parameter to determine the values of mp and bp.The range of-mp and mo was from 0 to 1,indicating that SVOCs in atmosphere were in steady state,and an equilibrium was just a special case when mp =-1 and mo = 1.The long-range atmospheric transport of POPs and their pathway to enter the Arctic air were investigated in present study by taking BDE-209 as an example.The results predicted by the steady-state model indicated that the chemicals with high K_OA values,like BDE-209,existing in both the gaseous and particulate phases in the atmosphere,not entirely in the particulate phase as predicted by the equilibrium models.Thus,we concluded that,it was mainly the gaseous BDE-209,not the particulate BDE-209,entered the Arctic atmosphere through the long-range atmospheric transport.In this study,a steady-state dynamic mass transfer model was established,the process of dynamic mass transfer between gas-and particle-phases was clarified,the characteristic time was calculated,the prediction level for a variety of SVOCs by the steady G/P partition model was investigated,the key factors affecting gas particle distribution G/P partition were analyzed,and two problems in G/P partition research were solved: 1)theoretical prediction equations and ranges of parameters m and b,2)Is gaseous or particulate BDE-209 that enters the Arctic atmosphere through LRAT? This work provided theoretical support for the further study of the G/P partition mechanism,prediction of SVOCs in terms of their global transport,and control of POPs in particular.