Project 2: Spatiotemporal Pollutant Tracking in the Atmosphere
Development of novel carbon nanotube sensors for carcinogenic PAHs and analysis of PAH chemical evolution in the air near Superfund Sites.
PROJECT LEADERS: JESSE KROLL, NOELLE SELIN, TIM SWAGER
This project is aimed at developing a new methodology (Spatiotemporal Pollutant Tracking) to assess the pathways by which pollutants are transported and transformed in the atmosphere. Researchers are working to apply Spatiotemporal Pollutant Tracking to improve estimates of potential exposures, and ultimately public health impacts, of hazardous environmental pollutants. Such information is critical for accurate risk assessment and the development of effective remediation policies, but is currently limited by uncertainties in atmospheric chemistry and transport. The atmosphere serves as an efficient medium for both the efficient transformation of pollutants (forming products that may be of higher or lower toxicity of the parent compound) and the rapid transport of pollutants (leading to large heterogeneities in their temporal and spatial distributions). The high reactivity and high variability of atmospheric pollutants is often not considered in exposure assessments, a critical gap that leads to substantial uncertainties in the ultimate environmental and health impacts of a given chemical.
In order to reduce such uncertainties, the researchers are developing a range of new state-of-the-art tools to better quantify chemical processing and transport through:
- Development and deployment of sensors to measure the concentrations of key atmospheric species;
- Laboratory studies of pollutant transformation in the atmosphere; and
- Modeling of contaminant chemistry and transport in order to predict pollutant concentrations and fate.
These three approaches are highly complementary, with outputs from each informing the other two. Central to this project is the study of not only the chemistry and distributions of the originally emitted compounds (“primary pollutants”), but also their multi-generation atmospheric transformation/ degradation products (“secondary pollutants”), which in some cases may be more hazardous than the precursor compound.
This project focuses initially on polycyclic aromatic hydrocarbons (PAHs), an important class of toxic compounds which has already undergone preliminary studies and will allow for the development of their methodology. Their methods are being extended and applied to nitrosamines (e.g., N-nitrosodimethylamine, NDMA) and ultimately to other compounds of interest. The improved characterization of atmospheric levels of these species inform studies in other environmental domains, and the improved ability to estimate human exposures and identify new target pollutants aid biomedical studies within the Center in determining the ultimate health impact of such chemicals.
Researchers engage the public, specifically communities in the Mystic River Watershed and tribal communities in northern Maine, by discussing sources and fates of atmospheric pollutants. The overarching goal is the development and application of new and innovative measurement and modeling approaches for the policy-relevant assessment of toxic substances.
Novel carbon nanotube technology enables detection of air contaminants at very low levels. This image shows a graphite pencil that ‘colors’ carbon nanotubes and enables detection of specific chemical contaminants (Tim Swager, Project 2).
Sensors that can selectively detect benzene, toluene, and xylene have been developed that make use of carbon nanotube-binding polymers to create binding (receptor) sites for these analytes. Sensor fusion using a combination of chemiresistance and quartz crystal resonator responses was used to selectively discriminate between analytes that have highly similar properties. These sensors exceed the required detection of benzene at the OSHA short-term exposure limit of 5 ppm in air (Tim Swager, Project 2).
The “minichamber” for the rapid oxidation of PAH-coated particles. The UV lights act as an “artificial sun” to generate oxidants, and particle composition is determined by online mass spectrometry. Collection of particle samples also enables offline analysis of chemical composition and particle toxicity (Jesse Kroll, Project 2).
Sample results from the oxidation of benzo[a]pyrene-coated particles by OH radicals. Total BaP decays with oxidation, forming particulate (and likely gas-phase) organic products; we have approximately half these products, but the remainder is an unresolved complex mixture, likely composed of a large number of different species (Jesse Kroll, Project 2).