Smog chambers are large enclosures (~ 10-200 m3) that are used to perform laboratory simulations of atmospheric reactions. By dealing with simple systems in which the number of reactants is limited and the conditions are strictly controlled, insights on how reactions proceed may be more easily realized than with real-world observations that are uncontrolled and inherently much more complex to analyze. A major focus of smog chamber research is the generation of secondary organic aerosol (SOA) that results from the reaction of gaseous hydrocarbons and inorganics (NOx) in the presence of simulated solar radiation. Of special interest is the relative SOA contribution of natural vs. anthropogenic hydrocarbon species. While until now methods have been developed to measure total SOA from such mixtures, very limited success has been achieved in determining the contribution from the individual hydrocarbons. However by arranging that the two hydrocarbons have different fractions of modern carbon and by measuring the fraction of modern carbon in the resulting SOA, the separate contributions of the two hydrocarbons may be readily calculated. These results can be compared to an alternative approach using GC-MS measurements of organic tracer compounds. A description of the experiment and results will be given, along with a discussion of potential distorting effects and their minimization.
Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.
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