Fate in Urban Areas

For photoreactive compounds such as PAHs, reaction in surface hlms can be their main degradative loss process in an urban system. Kwamena et al. (2004) and Poschl et al. (2001) found under experimental conditions that reactions of PAHs on organic-coated hlms exceeded those on atmospheric particulate matter (PM), the reason for which was not clear. Using these experimentally derived reaction rates in MUM, Kwamena et al. (2007) 

The importance of reaction losses in film for only BaP (and other low-volatility, high molecular weight PAHs) was ascribed to its tendency to partition into condensed phases (e.g. soil, PM, film), an order of magnitude greater ratio of surface area to volume of films on impervious surfaces (10 ) versus surface films on PM (10 ), and least important, the faster reaction rate in film versus PM. 

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As a compartment, films on impervious surfaces are highly dynamic, which is central to their impact on SOC fate in urban areas. Figure 19.2 illustrates the processes involved in film dynamics and chemodynamics. Depending on the location, the nature of the impervious surface, season, films grow and are rapidly lost through wash-off (Figure 19.3). 

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