Organic vapor-phase deposition distribution

The distribution of chemicals onto the foliar surface can occur by vapor-phase transfer, particle deposition (wet or dry), or from aqueous solution, which would be negligible for most organic compounds. It has been established that dry gaseous uptake is the predominant pathway for the foliar uptake of relatively nonvolatile compounds such as the chlorinated dibenzo-dioxins and -furans." The distribution of compounds between air and the cuticular polymer matrix follows Henry s law (Fig. 3.22)." This conclusion was drawn from observation of how a series of 50 low molecular weight (<175) compounds distributed between the vapor phase... 

Wet deposition may be an important source of PCBs to the Great Lakes. Unfortunately, like dry particle deposition, it is difficult to measure directly because of the low PCB concentrations, the problem of sampling artifacts, and the distribution of rain and PCB concentrations over space and time. Some trends are evident, however [ 189]. Snow has been shown to be much more effective than rain in scavenging PCBs from both vapor and particulate phases at a site in Minnesota [190,191]. This leads to a seasonal effect, in that precipitation concentrations of PCBs are highest in the winter in Chicago (Hites, personal communication), as with the concentrations of many other persistent organic pollutants [192], Possible reasons include sorption to an aqueous or... 

Once in the air, pesticides can exist as vapor, liquid aerosols or be sorbed/partitioned on dust and particulates. Even though in-depth information exists for particle phase distributions of organics in the atmosphere (24, 25, 26, 27, 28), few studies have appeared in the literature that assesses the vapor/aerosol distribution of pesticides under actual tropospheric conditions (29). Further research to determine how pesticides are distributed among atmospheric phases will be needed to better gauge the overall significance of wet/d deposition versus gas and particle-phase transformation processes occurring in air. 

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