UVM Theses and Dissertations
Format:
Print
Author:
Stevens, N. Tucker
Dept./Program:
Civil and Environmental Engineering
Year:
2010
Degree:
MS
Abstract:
Vehicle exhaust contains many unregulated chemical compounds that are harmful to human health and the natural environment. For example, vehicle exhaust gases and particulate matter (PM) contain polycyclic aromatic hydrocarbons (PAH), a class of organic compounds derived from fuel combustion that can be carcinogenic and mutagenic. PAHs have been quantified in vehicle-derived ultrafine particles (Dp<100nm), which are more toxic than larger particles and are linked to adverse health problems, including respiratory and cardiac disease. Once emitted into the atmosphere, particle-bound PAHs can undergo "aging" reactions with oxidants, such as ozone, to fbtm more polar species. These polar reaction products include species such as quinones that can be more toxic than the parent PAH compounds.
Here, 0.4ppm ozone was reacted over a 24-hour period with the 16 EPA priority PAHs plus coronene adsorbed to (i) a quartz fiber filter and (ii) NIST diesel PM. The difference in the PAH/03 heterogeneous reaction rate resulting from the two substrates will be discussed. The experiments were completed by spiking a known PAH mixture to the solid, reacting the samples with gas-phase ozone, and determinirtg; both PAH loss over time and products formed, using thermal-desorption gas chromatography / mass spectrometry (TD-GC/MS). The individual PAHs anthracene, phenanthrene, and fluorene, adsorbed to a QFF were also separately reacted with 0.4 ppm ozone.
A volatization control and the collection of volailized PAHs using a Tenax-packed thermal desorption vial completed the mass balance and aided determination parentproduct relationships. Heterogeneous reaction products analyzed directly without derivatization indicate the formation of 9,10-anthracenedione, 9H-fluoren-9-one, and (1,1 '-bipheny1)-2,2'-dicarboxaldehyde from the reaction of ozone with the PAH mix Oh a QFF, but onty 9,1 b-anthracehedione was detected for the diesel PM reaction. The heterdgeneous ozone reaction rate was slower for all but three PAHs for the PAH/DPM experiment versus the PAH/QFF experiment. The implications of these resuits for aging of diesel particulate in urban environments will be discussed.
Here, 0.4ppm ozone was reacted over a 24-hour period with the 16 EPA priority PAHs plus coronene adsorbed to (i) a quartz fiber filter and (ii) NIST diesel PM. The difference in the PAH/03 heterogeneous reaction rate resulting from the two substrates will be discussed. The experiments were completed by spiking a known PAH mixture to the solid, reacting the samples with gas-phase ozone, and determinirtg; both PAH loss over time and products formed, using thermal-desorption gas chromatography / mass spectrometry (TD-GC/MS). The individual PAHs anthracene, phenanthrene, and fluorene, adsorbed to a QFF were also separately reacted with 0.4 ppm ozone.
A volatization control and the collection of volailized PAHs using a Tenax-packed thermal desorption vial completed the mass balance and aided determination parentproduct relationships. Heterogeneous reaction products analyzed directly without derivatization indicate the formation of 9,10-anthracenedione, 9H-fluoren-9-one, and (1,1 '-bipheny1)-2,2'-dicarboxaldehyde from the reaction of ozone with the PAH mix Oh a QFF, but onty 9,1 b-anthracehedione was detected for the diesel PM reaction. The heterdgeneous ozone reaction rate was slower for all but three PAHs for the PAH/DPM experiment versus the PAH/QFF experiment. The implications of these resuits for aging of diesel particulate in urban environments will be discussed.