Relative source contribution, concept

This approach has also been applied to sources other than automobiles to assess the relative importance of various organics and sources. For example, Blake and Rowland (1995) used the concept of maximum incremental reactivity to assess the relative importance of various organics in Mexico City. They concluded that liquefied petroleum gas was a major contributor to ozone formation and that relatively small fractions of highly reactive alkenes in the gas contributed disproportionately to ozone formation. 

Evidence is accumulating that DOM composition selects specific taxa (see Chapters 9 and 14). Models show that the relative input rates of labile and humic DOM can determine which guilds of bacteria dominate community metabolism (see Chapter 18). Because there may be multiple input sources, varying in magnitude and composition, each community represents a solution to a cacophony of selective pressures. Source heterogeneity in terms of DOM composition or timing probably contributes to greater active diversity, unless response is limited by other environmental factors (e.g., low temperature or low pH). From this perspective, ambient DOM concentration and composition are products of the interaction between input sources and community activity. This conception makes clear the limitations of attempts to model microbial activity in terms of static analyses of DOM abundance or composition. 

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