Radiocarbon Content of PM2.5 Ambient Aerosol in Tampa, FL

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 μ g 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 ¹⁴C 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.

Acknowledgments

The United States Environmental Protection Agency through its Office of Research and Development managed and partially funded the research described here under Contract No. 68-D-00-206 to ManTech Environmental Technology, Inc. Funding was also provided by the Florida Department of Environmental Protection under Purchase Order No. S-3700-551920 to the University of Arizona. It has been subjected to Agency review and approved for publication.

We are grateful to EPA staff Leonard Stockburger for technical assistance throughout this project, Shelly Eberly for satellite map graphics and statistical assistance, and Bill Lonneman for fuel sample analysis; David Smith (Sunset Laboratory East) for OC/EC measurements; Alex Leonard (University of Arizona) for ¹⁴C measurements; Dwight Anderson (University of South Florida) for field sampling; Graham Bench (Lawrence Livermore National Laboratory) for identifying important differences for biomass combustion in residential heating versus wildfire settings; Bill Ellenson (ManTech Environmental Technology, Inc.—now Alion Science and Technology, Inc.) for contract management; and Tom Atkeson and Robert Stevens (Florida Department of Environmental Protection) for their funding support and encouragement.

Notes

¹Multiply by 0.277 to convert to μg m⁻³.

²m_B (pMC_F − pMC_B) / (m_F − m_B). See Equation (5).

¹Average uncertainty, ±10%.

²Corrected for positive organic artifact.

³(pMC_a/107) · 100.