Daily Variation in Particle-Phase Source Tracers in an Urban Atmosphere

Abstract

One full year of daily 24-hour fine particulate matter samples collected in East St. Louis, IL at the EPA funded St. Louis-Midwest Supersite were analyzed for organic carbon (OC), elemental carbon (EC) and non-polar organic tracers including polycyclic aromatic hydrocarbons (PAH(s)), hopanes, and alkanes. Two different analytical methods were used for analysis, solvent extraction gas chromatography/mass spectrometry (GCMS) and thermal desorption GCMS (TD-GCMS). The TD-GCMS method was equivalent to the solvent extraction GCMS method for key molecular markers. Select PAH(s) and alkanes were found to have extreme events within the annual study which had daily 24-hour concentrations that were 10 to 22 times higher than the annual average daily concentration. The OC and EC maxima were only 3 to 5 times higher than the annual average. To further assess the impact of point sources and to evaluate the compatibility of the two organic speciation methods, the six potential every sixth day annual averages were calculated and compared. The extreme concentration days were large enough, in the case of benzo[a]pyrene, to make every sixth day analysis not representative of the true annual average even with events greater than the 99th percentile of the annual distribution removed. The final analysis calculated day of the week averages for select representative organic tracers and revealed that gasoline motor vehicle tracers and OC do not have a distinct day of the week trend. EC, believed to be largely impacted by diesel exhaust, had a midweek concentration peak. These trends cannot necessarily be extrapolated to other urban areas or other events.

Acknowledgments

Field sampling and solvent extraction/GCMS analysis was funded wholly or in part by the United States Environmental Protection Agency (USEPA) through cooperative agreement R-82805901-0 (Michael Jones and Brenda Millar, Project Officers) and cooperative agreement X-98722301-0 (Michael Davis, Project Officer) to Washington University. This manuscript has not been subjected to the USEPA's required peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred. TD-GCMS analysis was funded by the Electric Power Research Institute (EPRI) through grant EP-P6095/C3075 (D. Alan Hansen, Project Officer) to Washington University, including partial funding by the Illinois Department of Commerce and Economic Opportunity (DCEO) grant 03-48313 to EPRI. The authors gratefully acknowledge the members of the St. Louis—Midwest Supersite consortium, including the field support provided by staff of the Air Quality Laboratory at Washington University in St. Louis.

Notes

¹Instrument dominated detection limits are listed by compound class and filter blank dominated detection limits are listed by compound when higher than the instrument detection limits.

²Average spike recovery and relative standard deviation are reported for compounds present in the quantification standards.

³Below detection.

¹Bold values represent the 3 highest monthly averages for each compound.