Exposure to traffic-related pollution during childhood has been associated with
asthma exacerbation, and
asthma incidence. The objective of the Cincinnati Childhood
Allergy and Air Pollution Study (CCAAPS) is to determine if the development of allergic and respiratory disease is associated with exposure to diesel
engine exhaust particles. A detailed receptor model analyses was undertaken by applying positive matrix factorization (PMF) and UNMIX receptor models to two PM₂.₅ data sets: one consisting of two
carbon fractions and the other of eight temperature-resolved
carbon fractions. Based on the source profiles resolved from the analyses, markers of traffic-related air pollution were estimated: the elemental
carbon attributed to traffic (ECAT) and elemental
carbon attributed to diesel
vehicle emission (ECAD). Application of UNMIX to the two data sets generated four source factors: combustion related
sulfate, traffic,
metal processing and soil/crustal. The PMF application generated six source factors derived from analyzing two
carbon fractions and seven factors from temperature-resolved eight
carbon fractions. The source factors (with source contribution estimates by mass concentrations in parentheses) are: combustion
sulfate (46.8%), vegetative burning (15.8%), secondary
sulfate (12.9%), diesel
vehicle emission (10.9%),
metal processing (7.5%),
gasoline vehicle emission (5.6%) and soil/crustal (0.7%). Diesel and
gasoline vehicle emission sources were separated using eight temperature-resolved organic and elemental
carbon fractions. Application of PMF to both datasets also differentiated the
sulfate rich source from the vegetative burning source, which are combined in a single factor by UNMIX modeling. Calculated ECAT and ECAD values at different locations indicated that traffic source impacts depend on factors such as traffic volumes, meteorological parameters, and the mode of vehicle operation apart from the proximity of the sites to highways. The difference in ECAT and ECAD, however, was less than one standard deviation. Thus, a cost benefit consideration should be used when deciding on the benefits of an eight or two
carbon approach.