Evaluation of Regional PM Predictions with Satellite and Surface Measurements

Author: Y. Zhang, Hilary E. "Ned" Snell, K. Vijayaraghavan and M.Z. Jacobson
October 17, 2005 - October 21, 2005
AAAR 2005 Annual Conference

Zhang, Y., H.E. Snell, K. Vijayaraghavan and M.Z. Jacobson, Evaluation of Regional PM Predictions with Satellite and Surface Measurements, AAAR 2005 Annual Conference, October 17-21, 2005, Austin, Texas.

The U.S. EPA Models-3/Community Multiscale Air Quality (CMAQ) modeling system is used to simulate the mass concentrations and optical properties of atmospheric particulate matter (PM) and to estimate the PM mass exported from the urban/regional scale to the global atmosphere. The simulation is conducted for the full year of 2001 with a horizontal resolution of 36 km for a domain that covers the contiguous U.S., southern Canada, and northern Mexico. The aerosol optical depths (AOD) and other aerosol radiative properties are calculated online using a parameterization of the Mie theory implemented in CMAQ and offline using several empirical approaches. The model results are evaluated using the measurements from satellite instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based monitoring networks such as the Interagency Monitoring of Protected Visual Environments (IMPROVE), the Aerometric Information Retrieval System-Air Quality System (AIRS-AQS), the Clean Air Status and Trends Network (CASTNet), and the Speciation Trends Network (STN). The evaluation is conducted in terms of spatial/temporal distributions of gas and PM species and quantitative statistical metrics that include both traditional measures such as the normalized mean bias (MNB) and new unbiased symmetric measures such as the normalized mean bias factor (NMBF). The process analysis tool in CMAQ is used to gain an indepth understanding of the controlling processes for the fate of PM and total odd oxygen (Ox) on urban/regional scales.

Our evaluation results for January-March 2001 have shown that CMAQ’s PM performance is generally consistent with current PM model performance, with worst performance at STN sites and relatively high biases in nitrate, ammonium, and organic carbon based on NMBF at all sites. CMAQ generally reproduces the magnitudes and spatial variations of the monthly-mean AOD obtained from MODIS. The single scattering albedo (SSA) predicted by CMAQ is within the typical range of satellite measurements. The process analysis has shown that the net export is 0.75 Gigamoles/day for Ox and 1.54 Gigagrams/day for PM2.5 out of the planetary boundary layer (0-2.9 km) during January-March 2001 over the entire modeling domain. Monthly and seasonal-mean results are being analyzed and contrasted. The predicted AODs with the online Mie parameterization will be compared with those from offline empirical approaches. Uncertainties and likely causes of discrepancies between simulation results and observations and between model results with different approaches for AOD calculations will be analyzed and identified.