大气中多溴联苯醚（PBDEs）的气粒分配的稳恒态理论的验证与完善

Semi-volatile organic compounds (SVOCs) are an important class of air pollutants, and its environmental behavior in atmosphere depends on their gas-particle (G/P) partitioning, which has been a research focus among environmental scientists world-wide for decades. The previous equation that has been used to predict the values of partition quotients, Kp for SVOCs (Harner-Bidleman Equation: logKpe=logKoa+logfom–11.91 where Koa is octanol-air partition coefficient and fom is organic matter content of the particles) was actually derived under equilibrium state, which cannot be used in many real cases. The applicant of this project has developed a steady-state theory in analyzing G/P partitioning behavior for polybrominated diphenyl ethers (PBDEs) and derived an equation to predict the values of Kp of PBDEs under steady state (Li et al. Atmos. Chem. Phys, 15, 1669-1681 2015): logKps=logKpe+loga, in which an equilibrium term (logKpe) and a non-equilibrium term (loga, caused by dry and wet depositions of particles) are included. The new equation is superior to the Harner-Bidleman Equation in predicting Kp for PBDEs. According to the steady-state equation, it was predicted that all the PBDE congeners have the same partition coefficient, logKp = -1.53 in the Arctic air (temperature < ~20 ℃) . Unfortunately, there are no data for the PBDE congeners other than BDE-209 available for confirmation of this prediction in the Arctic air. In this proposal, three places will be selected, including the County of Mohe in Heilongjiang Province, the coldest place in China, the City of Nanjing, one of the hottest cities in China, and the City of Harbin, as the air sampling sites, at which the ambient temperature range can be as high as ~90 ℃ (-50 ℃ − +40 ℃), almost reaching the global temperature range between -50 ℃ and +50 ℃. High volume air samplers will be used to collect air samples in both gas- and particle-phases twice a week for one year with more frequently sampling during coldest and hottest temperature periods. The concentrations of PBDEs in these samples will be measured, and the partitioning behavior of PBDEs in air at the wide temperature span will be studied. The objectives of this proposal are (1) to study the influence of the environmental parameters, including temperature, wind speed, and the fraction of organic matter (OM), to the G/P partition quotient of PBDEs; (2) to varify the prediction that all the PBDE congeners have the same partition coefficient, logKpsm = -1.53, at a low temperature (<~20 ℃); and (3) to improve the steady-state theory in G/P partition for PBDEs. We expect that the results derived in this NSF project will be useful for the environment scientists, in both modeling and monitoring areas, to study the environmental behavior of PBDEs in atmosphere, and can be extended to study the G/P partitioning behavior for other SVOCs.

半挥发性有机化合物(SVOC)在大气中的环境行为是由其气粒分配所决定的，因此建立能够准确预测SVOC的气粒分配份额(KP)的公式非常重要。在项目预实验阶段，申请人以多溴联苯醚(PBDE)为目标化合物，突破了气粒分配研究中的平衡态的理论框架，建立了气粒分配的稳恒态理论，并由此推导了稳恒态条件下计算KP的公式，此公式比基于平衡态的公式更能准确的描述PBDE的气粒分配规律。本项目拟在我国漠河、南京和哈尔滨设立大气采样点，采样温度范围可达~90 ℃(−50 ~ +40℃)，同步采集气粒两相样品和相应的环境参数，分析PBDE气粒两相的浓度数据；研究环境参数对KP的影响，找到稳恒态公式中参数的解析式；验证根据稳恒态公式做出的低温(<~20℃)条件下PBDE同系物的KP值为常数的预测，从而验证和完善气粒分配的稳恒态理论，为研究其它SVOC的气粒分配规律提供新的途径。

长期以来，在半挥发性化合物（SVOCs）的大气环境行为，包括SVOCs的大气传输、干湿沉降、长距离大气传输能力的研究都基于平衡态理论，即SVOCs在气相和颗粒相之间的分配遵循平衡态规律。我们于2015提出了 多溴联苯醚(PBDEs)在气相和颗粒相之间的分配的恒稳态理论，指出：由于PBDE的干湿沉降的存在，PBDE在气相和颗粒相之间的分配遵循恒稳态规律，并推导了PBDE恒稳态的气粒分配公式（Li-Ma-Yang Equation），而平衡态只是恒稳态在PBDEs 的干湿沉降可以忽略不计的情况下的一个特例。该项目是完善和推广这种推导时只适用于PBDE的气粒分配的恒稳态公式。通过该项目的实施，我们取得如下重要结果:.（1）我们推导的恒稳态的气粒分配公式（Li-Ma-Yang Equation）不仅适用于PBDE,还可以适用其它多种SVOCs.（2）Li-Ma-Yang模型比目前所有的模型能更准确地预测SVOC的气粒分配规律.（3）基于恒稳态的气粒分配公式，我们发现，当空气中TSP的浓度小于34 g/m3时，SVOC在大气中的气粒2相均匀分配的情况是不会发生的。因此用参数冷凝温度TC（SVOC在大气中的气粒2相均匀分配时的温度）做为对SVOC化合物进行分类的参量可能不妥 .（4）恒稳态的气粒分配公式应用的典型案例：基于恒稳态的气粒分配公式，提出了BDE-209主要是以气态，而不是颗粒态的形态，通过大气长距离迁移而进入北极。该研究结论颠覆了当前科学界的流行观点，具有典型的理论突破性质.（5）我们首次提出了SVOC的 logKP -log PL和logKP - logKOA的线性关系中的斜率m和截距b是由它们的固有参数KOA和PL决定的.（6）通过SVOCs气粒两相恒稳态建立的动力学过程的研究表明，SVOC在大气中达到恒稳态的时间要比达到平衡态的时间要短，有可能是几分钟或几小时，因此SVOC在大气中处于恒稳态或准恒稳态状态。.（7）我们的分析还表明，SVOC的气粒分配和颗粒沉积相互依赖。.我们创建的大气中半挥发性化合物气粒分配的恒稳态理论及其公式有很大的应用前景。应用该理论和公式，我们将对目前基于平衡态理论的一切模型和结论进行重新审视和修改，并创建基于恒稳态理论的SVOCs在多介质的环境形态理论系统。