A Retrospective Comparison of Model-Based Forecasted PM_(2.5) Concentrations with Measurements

摘要

This study presents an assessment of the performance of the Community Multiscale Air Quality (CMAQ) photo-chemical model in forecasting daily PM_(2.5) (particulate matter ≤2.5 μm in aerodynamic diameter) mass concen-trations over most of the eastern United States for a 2-yr period from June 14, 2006 to June 13, 2008. Model pre-dictions were compared with filter-based and continuous measurements of PM_(2.5) mass and species on a seasonal and regional basis. Results indicate an underprediction of PM_(2.5) mass in spring and summer, resulting from under-predictions in sulfate and total carbon concentrations. During winter, the model overpredicted mass concentra-tions, mostly at the urban sites in the northeastern United States because of overpredictions in unspeciated PM_(2.5) (suggesting possible overestimation of primary emissions) and sulfate. A comparison of observed and predicted di-urnal profiles of PM_(2.5) mass at five sites in the domain showed significant discrepancies. Sulfate diurnal profiles agreed in shape across three sites in the southern portion of the domain but differed at two sites in the northern portion of the domain. Predicted organic carbon (OC) profiles were similar in shape to mass, suggesting that discrepancies in mass profiles probably resulted from thernunderprediction in OC. The diurnal profiles at a highly urbanized site in New York City suggested that the over-predictions at that site might be resulting from overpre-dictions during the morning and evening hours, dis-played as sharp peaks in predicted profiles. An examination of the predicted planetary boundary layer (PBL) heights also showed possible issues in the modeling of PBL.