Seasonal abundance of organic molecular markers in urban particulate matter from Philadelphia, PA

Abstract

Organic molecular markers were measured in airborne particulate matter (PM10) from the City of Philadelphia North Broad Street air quality monitoring site to identify the seasonal abundance of key tracer compounds together with their dominant sources. Daily PM10 samples were collected seasonally in 2000 for four 2-week periods (January, April, August, and October). The North Broad Street site is within a heavily populated location in Philadelphia, PA. A suite of 52 individual organic marker compounds was monitored in the PM10 samples. Molecular markers, homologous compound series, and nonpolar and polar organic compounds were detected at ng m −3 ambient concentrations using gas chromatography/ion trap mass spectrometry (GC/IT MS). Organic diacids (C 3–C 9) and monoacids (C 10–C 30) had seasonal mass concentrations ranging from 91.0 (winter) to 261.8 ng m −3 (summer). Total n-alkanes (C 25–C 33) ranged from 25.9 (spring) to 49.5 ng m −3 (fall), total PAHs from 2.1 ng m −3 (summer) to 4.1 ng m −3 (winter), and total hopanes ranged from 4.0 ng m −3 (winter) to 7.4 ng m −3 (fall). The molecular marker ambient mass concentrations were normalized by the annual average mass of PM10 elemental carbon (EC) for the central Philadelphia area. The ambient mass concentrations to EC and OC ratios ranged from 2.6×10 −3 for total PAHs to EC to 115.3×10 −3 for total n-alkanoic acids to EC, 0.5×10 −3 for total PAHs to OC to 23.8×10 −3 for total n-alkanoic acids to OC. Ambient concentrations of individual markers are similar to other reported levels for metropolitan Los Angeles, CA and Atlanta, GA. Seasonal and daily variations of marker compounds are consistent with motor vehicle exhaust, particularly in winter. Summer concentration patterns indicate the importance of secondary organic aerosol to the PM10 ambient mass.