A Retrospective Comparison of Model-Based Forecasted PM_2.5Concentrations with Measurements

Abstract

This study presents an assessment of the performance of the Community Multiscale Air Quality (CMAQ) photochemical model in forecasting daily PM 2.5 (particulate matter Յ2.5 m in aerodynamic diameter) mass concentrations over most of the eastern United States for a 2-yr period from June 14, 2006 to June 13, 2008. Model predictions 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 underpredictions in sulfate and total carbon concentrations. During winter, the model overpredicted mass concentrations, 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 diurnal 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 the underprediction in OC. The diurnal profiles at a highly urbanized site in New York City suggested that the overpredictions at that site might be resulting from overpredictions during the morning and evening hours, displayed 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. INTRODUCTIONFine particles, (particulate matter [PM] with aerodynamic diameter Յ to 2.5 m in diameter, or PM 2.5 ) have been linked to various health effects including asthma and cardiac arrest. 1,2 The U.S. Environmental Protection Agency (EPA) promulgated the annual and daily PM 2.5 National Ambient Air Quality Standard (NAAQS) in 1997 and again revised it in 2006. The revised PM 2.5 NAAQS consists of a 24-hr daily standard of 35 g/m 3 and an annual standard of 15 g/m 3 . Historically, most daily air quality forecasts for a region have been based on a combination of statistical methods and human judgment using point measurements at observational sites. In contrast, the application of a three-dimensional air quality model can provide spatially and temporally resolved forecasts, but its use in real-time forecasts in the past was often limited by computational speed. Because of increases in computational speeds and the maturity of air quality models, the past decade has witnessed the emergence of model-based forecast guidance as an increasingly relevant component of air quality forecasting for ozone [3][4][5][6][7][8][9][10][11][12] and PM 2.5 11,13,14 concentrations. The increased availability of forecast guidance based on photochemical models had stimulated interest in the assessment of the performance of these models when applied in a forecasting mode. This study repo...

Mercury Wet Deposition and Speciated Air Concentrations from Two Urban Sites in New York State: Temporal Patterns and Regional Context

“…The panels in Fig. 7 show the average diurnal variation of the PBL heights at both sites during the winter and summer, estimated from a model-based air quality forecast platform (Doraiswamy et al, 2010), as well as the diurnal variation in air temperature. The Bronx site exhibits a larger winter-summer contrast in afternoon PBL heights, with summertime afternoon PBL heights nearly a factor of four higher than nocturnal PBL heights (compared to a factor three at Rochester) due to a stronger heat island and more complex land/water circulation patterns.…”

Long Term Black Carbon Measurements at Two Urban Locations in New York

“…The weather forecast product consisted of the 12:00 coordinated universal time cycle forecasts of the National Center for Environmental Prediction (NCEP) operational 12-km, WRF-NMM based North American Mesoscale model, which had already been processed by the NCEP WRF postprocessor. PBL heights were extracted for the grid cells in which the air monitoring stations were located (Doraiswamy et al, 2010).…”

Application of Remote Sensing Instrument in Air Quality Monitoring

“…In fact, unlike natural vegetation surfaces, the convective sensible heat flux remains positive over the diurnal cycle through release of heat stored the urban canopy. This mechanism is particularly important for air quality predictions since collapse of the urban boundary layer (UBL) due to underestimates in the turbulent flux can result in dramatic increases in surface pollution forecasts (Doraiswamy et al, 2010). For these reasons, direct evaluation of the UBL height is important in diagnosing the performance of operational air quality models driven by high resolution meteorological forecasts.…”

“…During these retrospective analyses, when using the PX Land Surface Model, the pixel nearest the urban CCNY validation site is classified as 88% "Urban and Build-Up land" as defined by the USGS 24 land use category (Anderson et al, 1976). Finally, we also want to restate that our study is limited to summer where the biggest air quality issues regarding particulates in an urban environment occur and the most severe difficulties in the diurnal structure of the CMAQ air quality forecasts seem to occur (Doraiswamy et al, 2010). While summer 2007 measurements used retrospective analysis, summer 2010 forecast data were made using the MYJ PBL scheme which uses the 1.5-order (level 2.5) turbulence closure model of Mellor and Yamada (1982) to represent turbulence above the surface layer (Janjic 1990(Janjic , 1994(Janjic , 2001) and has become a popular model for PBL representation.…”

“…8, a strong diurnal spike behavior is observed in the CMAQ surface layer PM2.5 which is not seen in the TEOM measurements. The direct source of this over bias is not clear with possible contributing factors being unrealistic gradients in the PM2.5 vertical profiles or overestimation in the primary emission associated with urban rush hour traffic (Doraiswamy et al, 2010). However, the use of ceilometer backscatter profile data can be used to explore how realistically, the primary emissions are distributed vertically.…”