Citation:

Nolte, Chris, W. Appel, J. Kelly, P. Bhave, K. Fahey, J. Collett, Jr., L. Zhang, AND Jeff Young. Evaluation of the Community Multiscale Air Quality (CMAQ) modeling system against size-resolved measurements of inorganic particle composition across sites in North America. Geoscientific Model Development . Copernicus Publications, Katlenburg-Lindau, Germany, 8(9):2877-2892, (2015).

Impact/Purpose:

The National Exposure Research Laboratory’s Atmospheric Modeling Division (AMAD) conducts research in support of EPA’s mission to protect human health and the environment. AMAD’s research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation’s air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.

Description:

This work evaluates particle size-composition distributions simulated by the Community Multiscale Air Quality (CMAQ) model using Micro-Orifice Uniform Deposit Impactor (MOUDI) measurements at 18 sites across North America. Size-resolved measurements of particulate SO₄, NO₃^-, NH₄⁺, Na⁺, Cl^-, Mg²⁺, Ca²⁺ and K⁺ are compared to CMAQ model output for discrete sampling periods between 2002 and 2005. The observation sites were predominantly in remote areas (e.g. National Parks) in the United States and Canada, and measurements were typically made for a period of roughly one month. For SO₄^2- and NH₄⁺, model performance was consistent across the U.S. and Canadian sites, with the model slightly overestimating the peak particle diameter and underestimating the peak particle concentration compared to the observations. Na⁺ and Mg^{2+ size distributions were generally well represented at coastal sites, indicating reasonable simulation of emissions from sea spray. CMAQ is able to simulate the displacement of Cl- in aged sea spray aerosol, though the extent of Cl- depletion relative to Na+ is often underpredicted. The model performance for NO3- exhibited much more site-to-site variability than that of SO₄2- and NH₄>+, with the model ranging from an underestimation to overestimation of both the peak diameter and peak particle concentration across the sites. Computing PM_2.5 from the modeled size distribution parameters rather than by summing the masses in the Aitken and accumulation modes resulted in differences in daily averages of up to 1 µg m-3 (10%), while the difference in seasonal and annual model performance compared to observations from the IMPROVE, CSN and AQS networks was very small. Two updates to the CMAQ aerosol model—changes to the assumed size and mode width of emitted particles and the implementation of gravitational settling—resulted in small improvements in modeled size distributions.}

URLs/Downloads:

INITIAL FINAL CMAQ_SIZEDIST_EVAL_2015-03-05-CLEAN.PDF  (PDF, NA pp,  1107.516  KB,  about PDF)

Geoscientific Model Development  

Record Details:

Record Type:DOCUMENT( JOURNAL/ PEER REVIEWED JOURNAL)

Product Published Date:09/15/2015

Record Last Revised:10/28/2015

OMB Category:Other

Record ID: 309970

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