Detection, Spatial Analysis and Source Apportionment of Polycyclic Aromatic Hydrocarbons using a Mobile Aerosol Mass Spectrometer

OLADAYO OLADEJI, Albert A. Presto, Sunhye Kim, Carnegie Mellon University

     Abstract Number: 391
     Working Group: Source Apportionment

Abstract
Polycyclic Aromatic Hydrocarbon (PAH) are semi volatile organic compounds, generated from the incomplete combustion of organic compounds, that can be harmful to human health. They are a part of air toxics that can cause serious health effects even at extremely low levels.

There has been limited information on the spatial distributions of PAHs in cities in part because of a lack of real-time, chemically specific methods. The Aerosol Mass Spectrometer (AMS) is well suited for mobile sampling that can generate citywide concentration maps. The AMS is also sensitive to some PAHs, several of which are detected at the parent ion mass-to-charge ratio.

This study seeks to identify, quantify, spatially analyze, and provide a source apportionment of particle-phase PAHs using mobile AMS sampling. Sampling was done in Pittsburgh. A mobile laboratory was driven over defined routes in areas of varying source activity (e.g., the downtown core, residential areas, and industrial areas).

We quantified concentrations of Acenaphthene, Acenaphthylene, Naphthalene alongside other PAHs, as well as oxy-PAHs with the AMS. The concentrations of most reduced PAHs were both spatially and temporally variable. For instance, the mean concentration of Acenaphthene varied by a factor of 3 between neighborhoods. Most of the detected PAHs had low background concentrations and the time series of concentration was dominated by short intense concentration spikes.

PAH concentration spikes were correlated with black carbon (BC), suggesting vehicle emissions as a major source. Ratio-ratio plots (e.g., PAH/BC) suggest that most of the observed spikes can be attributed to emissions from nearby gasoline and diesel vehicles, with diesel vehicles being the dominant source.