Development of a regional-scale pollen release and transport modeling framework for investigating the impact of climate change on allergic airway disease

To investigate how pollen occurrence may be influenced by climate change and interact with anthropogenic pollutants to affect human health in a changing world, a new model of pollen emissions from terrestrial, temperate vegetation has been developed and incorporated into the WRF/CMAQ regional air-quality modeling framework. The pollen emission model, a module of the Model of Emissions of Gases and Aerosols from Nature is driven by meteorological variables and is designed to be sensitive to potential climate shifts and is flexible with respect to the vegetation species and plant functional types (PFTs) represented. The initial evaluation of the model focuses on pollens from important allergenic tree, grass, and weed species present in a model domain centered over southern California during Mar-Jun 2010. Vegetation cover and species composition data were drawn from numerous datasets and a database of allergenic vegetation species, their pollen potential, and relative allergenicities has been developed. PFT-specific pollen release modules with mechanisms that vary according to the Köppen climate classification of the simulation area are described. In general, for the moderate Mediterranean and oceanic climate zones encompassing the most populous fraction of the southern California domain, temperature is the main driver controlling the timing of pollen release while precipitation controls the total amount of pollen produced by the species selected for simulation. For the initial evaluation period, 30-arc second monthly-mean precipitation data for 1971-2000 and Oct 2008 to Dec 2009 from the Parameter-elevation Regressions on Independent Slopes Model (PRISM) are used to estimate the total amount of pollen available for each species. 4-km x 4-km temperature results from the WRF (Weather Forecasting and Research) model for Oct 2009 to Jun 2010 are used to model the onset of pollen season. Once emitted into the atmosphere, the CMAQ (Community Multiscale Air Quality) chemical transport model derives ambient pollen concentrations by adding the pollen from each species as a tracer. Concentrations of O3 and PM2.5 (particulate matter with aerodynamic diameter less than 2.5 microns), which can exacerbate allergenic responses, are also modeled by CMAQ. To evaluate the CMAQ results, modeled O3 and PM2.5 concentrations are compared to data from the US EPA Air Quality System. Modeled pollen concentrations are evaluated against data collected at University of Southern California's Children's Health Study (CHS) sampling sites during summer 2010. For future work, the modeled pollen, O3, and PM2.5 concentrations will be used to derive the concentration response function for overall and species-specific allergen concentrations on key respiratory health outcomes using data obtained from the CHS.