A highly sensitive method was developed for measuring polycyclic aromatic hydrocarbons and nitro-substituted polycyclic aromatic hydrocarbons in ambient aerosol. Using large volume injection, this technique provided an order of magnitude increase in sensitivity compare to conventional injection techniques. This method facilitated the measurement of the first reported diurnal size distribution of NPAHs. Size resolved samples were collected using a Berner low-pressure impactor deployed at the Baltimore PM_2.5 Supersite in April 2002. Both classes of compounds were found predominantly on particles less than 0.49μm with similar size distributions among samples for most of the 12 hr periods. A linear relationship between compound geometric mass median aerodynamic diameter (GMMAD) and log sub-cooled vapor pressures ( p_l°) was observed for PAHs and NPAHs, respectively, during each sampling period. The inter-relationhips between the slopes and y-intercepts from the GMMAD/log vapor pressure correlations suggest the source of PAHs to the Baltimore atmosphere reside on particles with GMMADs equal to 0.18 μm, consistent with vehicle emissions.

Bulk organic aerosol was collected in Baltimore, MD during the spring, summer and winter of 2002-2003. Concentrations of n-alkanes, hopanes, polycyclic aromatic hydrocarbons (PAH), and nitro-substituted polycyclic aromatic hydrocarbons (NPAH) were measured in the gas and particle phase. The organic compounds varied little, with seasonal concentrations typical of North American urban atmospheres. Principal Components Analysis/Multiple Linear Regression (PCA/MLR) and Positive Matrix Factorization (PMF) were used to determine the sources of individual compound classes (PAHs, NPAHs, hopanes and alkanes) and total particulate carbon and PM_2.5 to the Baltimore atmosphere for during 2002-2003. PMF was used to determine the total carbon and PM_2.5 source estimates to the Baltimore atmosphere. The sources identified included tire wear/road dust, gasoline and diesel exhaust, oil combustion, biogenic, secondary organic aerosol, incineration, and coal explaining 64% of the variability in the total carbon and PM_2.5 concentrations.