Spatial variations of source contributions to fine organic carbon (OC) and fine particles in the southeastern United States were investigated using molecular marker-based chemical mass balance modeling (CMB-MM) and carbon isotope analysis. Nine primary emission sources were resolved with wood combustion (average 1.73 μg m−3, 23 ± 14% of measured OC) being the most dominant contributor to OC, followed by gasoline engine exhaust (0.45 μg m−3, 6.1 ± 6.2% of OC), diesel engine exhaust (0.43 μg m−3, 4.8 ± 4.1% of OC), and meat cooking (0.30 μg m−3, 4.1 ± 2.6% of OC). Measurable contributions from vegetative detritus, cigarette smoke, road dust, and natural gas exhaust were found. The impact of coke facilities was estimated for the first time in Birmingham, Alabama, and contributed 0.52 μg m−3 on average to fine OC. The unexplained OC accounted for 54 ± 26% of measured OC, possibly because of contributions from secondary OC, other unidentified primary sources and the possible positive artifact of OC. The urban excess of OC from diesel exhaust, gasoline exhaust and meat cooking can be seen from the results of the urban-rural pair in Alabama. Detailed chemical analysis revealed the wood burning episode at the rural site and an episode of secondary formation in the study region. The 14C analysis, a tool to study the relative contributions of contemporary and fossil carbon contents of fine particles, agreed well with the CMB-MM analysis. Both reflected a higher fossil fraction of carbon at urban sites especially in Birmingham, Alabama.
A method to measure C-13/ C-12 ratios of individual carbon fractions of airborne particular matter (PM) from filter samples using a stepwise thermal desorption/combustion OC/EC analyzer (via thermal optical transmission, (TOT) coupled with gas chromatography separation, followed by isotopic ratio mass spectrometer (GC-IRMS) analysis has been developed. In the TOT instrument, carbon fractions are released at different temperature ranges and different redox conditions. Organic carbon fraction (OC) was released at a relatively low temperature (T = 550 degrees C), whereas, elemental carbon or black carbon fraction (EC or BC was released at a high temperature (T > 800 degrees C) via combustion. A temperature step of 870 degrees C without oxygen was chosen to remove the impact of carbonate carbon (CC) and possible crossimpact from OC and EC. All the fractions were collected cryogenically and subject to carbon isotope measurements via GC-IRMS. To evaluate the precision, accuracy and linearity range of the measurements, the different types of blanks and standards were investigated, including OC (i.e. glucose, sucrose, n-Alkanes and polycyclic aromatic hydrocarbons (PAHs), CC (i.e. carbonates) and EC (i.e. carbon black and graphite). The overall precision and the accuracy of the method is similar to 0.3 parts per thousand. The method was applied to Pacific2001 aerosol samples from the Greater Vancouver area in Canada. The results show that good baseline separations in thermographs can be achieved for individual carbon fractions (i.e. OC and EC) using optimized temperature plateau and retention times; relative small difference in carbon isotopic composition between OC and EC (Delta(13) C-OC-(EC) = delta C-13(OC)delta C-13(EC)) were found in tunnel samples, whereas, the largest Delta C-13(OC-EC) were obtained in forest air samples; the Delta C-13(OC-EC) in ambient PM is likely dependant upon the dominant sources present in the vicinity of the sampling sites; the distribution of 13C/ 12 C ratios of OC/EC can provide useful information for source characterization and apportionment of ambient particulate matter. (c) 2006 Elsevier Ltd. All rights reserved.