Abstract of PhD Thesis

Linking Urban Air Field Measurements of Particulate Matter to their Chemical Analysis and Effects on Health

David Healy, University College Cork (2008)

Whilst internationally collected data demonstrating that adverse human health effects correlate with Particulate Matter (PM), major questions, concerning the mechanism(s) by which they act, remain. It is hypothesized that these heterogeneous effects may be attributed partly to the differences in the elemental composition of PM.

Airborne particulate samples were collected in Cork, Ireland during two sampling campaigns from a total of four different sampling sites.

In the first campaign PM10, PM10-2.5 and PM2.5 levels from a Cork urban site were gravimetrically analysed over a six year period. Contributions made by the fine fraction to PM10 levels were compared to those made by the coarse fraction. Annual average PM2.5 concentrations at the Cork urban sampling site ranged from 8.32 to 13.8 µg/m3, with an overall six year mean of 10.7 µg/m3. Compositional analysis was found to be suggestive of the possible influence of maritime traffic on Cork’s City urban air quality and indeed the effect it may have on the Cork City Council’s urban air monitoring site.

The second sampling campaign focused on the size fraction PM2.5-0.1 collected by means of a High Volume Cascade Impactor (HVCI) sampler. Seasonal analysis of samples highlighted winter to be the season with the greater association between the fine fraction (PM2.5-0.1) and PM10, where R2 = 0.81 and M = 0.5, compared to the coarse fraction (PM2.5-10). A linear relationship of the form:

(HVCI PM10-0.1) = 0.94 (Partisol PM10)

was identified between the samplers used during both campaigns, where Partisol = low volume air sampler. Chemical analysis of samples showed that metals such as Ni, Zn, Cu, Pb, Cr and V were predominantly more evident in the fine fraction compared to that of the coarse. The Cation-to-anion ratios of the inorganic ions (PM2.5-0.1) were found to be close to unity. A summer depletion of levels of chloride ions were noted in the particulate samples when compared to other seasons. Major secondary inorganic aerosol species in the Cork atmosphere such as (NH4)2SO4 and NH4NO3 were identified. The presence of NaCl was evident at all sampling sites.

To examine the relative toxicity of the collected ambient PM2.5-0.1 samples, human epithelial lung cells, A549, were exposed (in vitro) to three different concentrations (5.5, 11 and 22 μg/cm2) of particulates. Release of interleukin (IL)-6, IL-8, TNF-α and generation of intracellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) were measured. All samples, in the absence of cytotoxicity determined by the resazurin and lactate dehydrogenase assays, at three different concentrations induced intracellular ROS and release of IL-6 and IL-8 but not TNF-α after 72 hr exposure to PM2.5-0.1. The urban samples showed a consistent ability to increase the production of intracellular ROS, measured by dichlorofluorescein acetate, irrespective of the season.

Links between the chemical composition of the PM and its corresponding toxicity profile were identified by Principal Component analysis. Results indicated that the transition metals were linked to the generation of ROS and that these components exert their biological effects in an additive manor, coupled with the inorganic ions that dictate acidity. Subsequently it was also demonstrated that the chemical composition of ambient PM varied according to season along with the biological effect it induced in vitro.