Vapor/aerosol distribution

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. 

Duinker JC, Bruchertall F (1989) On the distribution of atmospheric polychlorinated congeners between vapor, aerosols, and rain. Environ Sci Technol 23 57-62 Fernandez P, Grimalt JO (2003) On the global distribution of persistent organic pollutants. CHIMIA 57 514-521... 

Be dispersed as vapors or by aerosols within an enclosed area (e.g., building, tunnel) where the ventilation system would further distribute the agent... 

FIGURE 7.13 Schematic of an evaporative light scattering detector. The three stages are nebulization, in which column effluent is aerosolized evaporation, in which the mobile phase is vaporized and optical detection, in which the light scattering of the residual solute particles is recorded. Some detectors also include an obstacle in the flow path for droplet discrimination, which leads to a more homogenous distribution of droplet sizes. 

As we have seen in Chapter 9, there are a variety of dissolved solutes in atmospheric particles, which will lower the vapor pressure of droplets compared to that of pure water. As a result, there is great interest in the nature and fraction of water-soluble material in atmospheric particles and their size distribution (e.g., Eichel el al., 1996 Novakov and Corrigan, 1996 Hoffmann et al., 1997). This vapor pressure lowering effect, then, works in the opposite direction to the Kelvin effect, which increases the vapor pressure over the droplet. The two effects are combined in what are known as the Kohler curves, which describe whether an aerosol particle in the atmosphere will grow into a cloud droplet or not under various conditions. 

Evaporative decomposition erf solutions and spary pyrolysis have been found to be useful in the preparation of submicrometer oxide and non-oxide particles, including high temperature superconducting ceramics [819, 820], Allowing uniform aerosol droplets (titanium ethoxide in ethanol, for example) to react with a vapor (water, for example) to produce spherical colloidal particles with controllable sizes and size distributions [821-825] is an alternative vapor phase approach. Chemical vapor deposition techniques (CVD) have also been extended to the formation of ceramic particles [825]. 

Baeckstroem K, Nilsson PG. Measurements of droplet size distributions from metered dose inhalers with different vapor pressures and contents of surfactant. J Aerosol Sci 1988 19(7) 1097-1100. 

Size-resolved chemical information is much more difficult to obtain. The many applications of the differential mobility analyzer in measuring properties of size-classified particles are important tools for the characterization of aerosol systems, but the approaches demonstrated to date yield limited data. Vapor pressures, surface tension, and optical absorption have been measured on mobility-classified aerosols. Direct measurements of the distribution of chemical composition with particle size are needed. Elemental... 

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