| Abstract
| - Individual organic compounds often referred to asmolecular markers are used in conjunction with thechemical mass balance (CMB) model to apportion sourcesof primary organic aerosol. This paper presents amethodology to visualize molecular marker data; it allowscomparison of ambient data and source profiles andallows assessment of chemical stability and aging. Themethod is intended to complement traditional quantitativesource apportionment analysis. The core of the techniqueinvolves construction of plots of ratios of speciesconcentrations (ratio−ratio plots) in which source profilesappear as points connected by linear mixing lines. Theapproach is illustrated using data collected over a 1-yearperiod in Pittsburgh, Pennsylvania. The analysis considersfor elemental carbon and a number of high molecular weightpolycyclic aromatic hydrocarbons (PAHs) commonlyused as molecular markers in CMB: benzo(b+j+k)fluoranthene, benzo(e)pyrene, benzo[g,h,i]perylene, coronene,and indeno(1,2,3-cd)pyrene. In Pittsburgh, the ambientconcentrations of these PAHs are higher than in other citiesin the United States; they are also strongly correlatedconsistent with a single, dominant source. Both ratio−ratio plots and CMB analysis indicate that this source ismetallurgical coke production. Although emissions from cokeproduction dominate ambient PAH concentrations, onmost study days they contributed little fine particle mass.Ratio−ratio plots are then used to investigate thefeasibility of using PAHs to help differentiate betweengasoline and diesel vehicle emissions. Ambient concentrationsof these large PAHs provide little information on thegasoline−diesel split because of the strong influence oflocal emissions from coke production combined with evidenceof photochemical decay of PAHs in the regional airmass. Decay of PAHs will bias estimates of the gasoline−diesel split toward diesel emissions.
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