MODELING SPATIOTEMPORAL VARIABILITY OF INTRA-URBAN AIR CONTAMINANTS IN THE DETROIT AIRSHED: A PRAGMATIC APPROACH

Ambient air pollution models inform epidemiological studies of health outcomes related to chronic exposure to air contaminants in urban areas. These models are derived from various sources of information. Regional air quality monitors provide long-term measurements with high temporal resolution, but commonly lack the spatial resolution needed to provide neighborhood-scale exposure estimates. In contrast, temporary, closely spaced networks of samplers can provide high spatial resolution measurements over short, discontinuous periods of time but are expensive to repeat over extended time periods. Therefore, practical methods are needed to assimilate detailed temporal data with high spatial resolution information to generate high spatiotemporal resolution models of urban air pollution.

This study combined a three-year air contaminant time series from the Michigan Air Sampling Network (MASN) with spatially detailed data sets for two two-week periods in September 2008 and June 2009 to produce monthly contaminant concentration maps across the city of Detroit, Michigan, from January 2008 through December 2010. Two geochemical analytes, NO₂ and total BTEX, as well as two particulate matter size fractions, PM_2.5 and PM₁₀ were investigated. The September 2008 and June 2009 data sets were modeled using ordinary kriging to produce high spatial density concentration maps with 300m by 300m resolution across the city. A weighted average was applied to these maps to interpolate monthly concentration estimates between September 2008 and August 2009. Temporal variability was then incorporated by adjusting the weighted average spatial maps using a monthly average bulk shift derived from MASN time series measurements. The resulting maps incorporate seasonal trends while preserving neighborhood scale spatial variation. Results are being applied in a larger study designed to assess the relationship between adverse birth outcomes and air pollution in the city of Detroit.