Radiocarbon (~(14)C) measurements showed substantial levels of biogenic carbon,52 to 89,in PM2.5 samples collected near Tampa,Florida,during May 3-22,2002.Nighttime biogenic percentages tended to be higher than daytime percentages.The average PM2.5 biogenic carbon concentration was 2.4 mug m~(-3).The ~(14)C (and carbon mass concentration) results were highly reproducible,based on duplicate analyses of samples from collocated samplers.The work includes a first-time treatment of the potential for distortion of the ~(14)C results by organic artifact during sampling,and a re-consideration of the impact on present-day ~(14)C results of the mid-twentieth century "bomb" effect.Neither was found to have a significant impact on the ~(14)C results.Concurrent organic and elemental carbon measurements were used to provide estimates of secondary organic aerosol (SOA) in the samples.The results of this study closely resemble those found in other summertime studies near Nashville,Tennesse (1999) and near Houston,Texas (2000) with regard to the joint importance and connection of biogenic PM2.5 and SOA in the Southeastern U.S.during summertime.
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