Air Quality Modeling of PM and Air Toxics at Neighborhood Scales

With current interest in fine particles and toxics pollutants, there is opportunity to extend air quality models to add capability for improving exposure assessments. Current state of science air quality modeling capability do not yet provide an explicit and proven link between modeled concentration fields, data from fixed site and personal exposure monitors, and human exposure models. Mechanisms for adverse health under investigation now include numerous causal hypotheses including pollutants' concentration loading as well as their chemical constituents and physical properties. However, the distribution of concentration fields for different causal pollutants may be highly complex at neighborhood scales. The location and temporal sampling of typical networks in urban areas are sparse, and the resulting concentration fields are thus poorly resolved. Current emissions based modeling systems (such as in Models-3 Community Multiscale Air Quality Modeling System (CMAQ) capability to model PM 2.5 and PM-10 from horizontal resolution ranges from regional (~36km) to urban scales (4km) are currently being tested and evaluated. Since urban areas introduce fresh sources of pollutants into a regional background, we anticipate subgrid spatial variability of the concentration fields to be significant with commensurate impact on subsequent exposure levels. Stationary monitors used to drive human exposure models will be limited in their ability to characterize this variability. Current emissions-based air quality models have limited spatial resolution. Models of dispersion of local sources ignore the regional background. Methods to serve as a bridge between these modeling and monitoring approaches to determine concentration variation arising from the juxtaposition of concentration from the regional and urban sources are needed.

In this presentation, a modeling R&D investigation to rationally link emissions-based modeling with ambient and exposure monitors to provide concentration fields as critical inputs to models of human exposure (and epidemiological studies) is described. This initial proof on concept-requirement analyses study includes deriving various functional linkages between the Models-3/CMAQ emissions based modeling system concentration fields of key particulate matter parameters with ambient fixed site and personal exposure monitoring data, and incorporating into the methodologies, flow visualization, computational fluid dynamics modeling and statistical techniques. Specific aspects under study include developing of functional relationships that provides a mapping across space and time between the modeled and monitored fields, considerations of sensitivities to model grid resolution, for different emissions scenarios, and for different averaging time periods ranging from hourly to annual fields. The effort will include methods for modeling human exposures to a variety of human activities.

*On assignment to the National Exposure Research Laboratory, U.S. Environmental Protection Agency