Gaseous VOCs rapidly modify particulate matter and its biological effects – Part 1: Simple VOCs and model PM S. Ebersviller1, K. Lichtveld1, K. G. Sexton1, J. Zavala1, Y.-H. Lin1, I. Jaspers1,2, and H. E. Jeffries1 1Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, USA 2Center for Environmental Medicine and Lung Biology, Human Studies Facility, The University of North Carolina at Chapel Hill, USA
Abstract. This is the first of a three-part study designed to demonstrate dynamic
entanglements among gaseous organic compounds (VOC), particulate matter (PM),
and their subsequent potential biological effects. We study these entanglements
in increasingly complex VOC and PM mixtures in urban-like conditions in a large
outdoor chamber. To the traditional chemical and physical characterizations of
gas and PM, we added new measurements of biological
effects, using cultured human lung cells as model indicators. These biological
effects are assessed here as increases in cellular damage or expressed
irritation (i.e., cellular toxic effects) from cells exposed to chamber air
relative to cells exposed to clean air. The exposure systems permit virtually gas-only- or
PM-only-exposures from the same air stream containing both gases and PM in
equilibria, i.e., there are no extractive operations prior to cell exposure.
Our simple experiments in this part of the study were designed to eliminate many
competing atmospheric processes to reduce ambiguity in our results. Simple volatile
and semi-volatile organic gases that have inherent cellular toxic properties were
tested individually for biological effect in the dark (at constant humidity).
Airborne mixtures were then created with each compound to which we added PM that
has no inherent cellular toxic properties for another cellular exposure.
Acrolein and p-tolualdehyde were used as model VOCs and mineral oil
aerosol (MOA) was selected as a surrogate for organic-containing PM. MOA is
appropriately complex in composition to represent ambient PM, and exhibits no
inherent cellular toxic effects and thus did not contribute any biological
detrimental effects on its own.
Chemical measurements, combined with the responses of our biological exposures,
clearly demonstrate that gas-phase pollutants can modify the composition of PM
(and its resulting detrimental effects on lung cells). We observed that, even if the gas-phase
pollutants are not considered likely to partition to the condensed phase, the
VOC-modified-PM showed significantly more damage and inflammation to lung cells
than did the original PM. Because gases and PM are transported and deposited
differently within the atmosphere and the lungs, these results have significant
consequences for a wide range of people.
For example, current US policies for research and regulation of PM
do not recognize this "effect modification" phenomena (NAS, 2004).
These results present an unambiguous demonstration that – even in these simple
mixtures – physical and thermal interactions alone can cause a modification of
the distribution of species among the phases of airborne pollution mixtures
that can result in a non-toxic phase becoming toxic due to atmospheric thermal processes
only. Subsequent work (described in companion papers) extends the simple results
reported here to systems with photochemical transformations of complex urban mixtures
and to systems with diesel exhaust produced by different fuels.
Citation: Ebersviller, S., Lichtveld, K., Sexton, K. G., Zavala, J., Lin, Y.-H., Jaspers, I., and Jeffries, H. E.: Gaseous VOCs rapidly modify particulate matter and its biological effects – Part 1: Simple VOCs and model PM, Atmos. Chem. Phys., 12, 12277-12292, doi:10.5194/acp-12-12277-2012, 2012.