MIRAGE: Model Description and Evaluation of Aerosols and Trace Gases
The MIRAGE (Model for Integrated Research on Atmospheric Global Exchanges) modeling system, designed to study the impacts of anthropogenic aerosols on the global environment, is described. MIRAGE consists of a chemical transport model coupled on line with a global climate model. The chemical transport model simulates trace gases, aerosol number, and aerosol chemical component mass [sulfate, MSA, organic matter, black carbon (BC), sea salt, mineral dust] for four aerosol modes (Aitken, accumulation, coarse sea salt, coarse mineral dust) using the modal aerosol dynamics approach. Cloud-phase and interstitial aerosol are predicted separately. The climate model, based on the CCM2, has physically-based treatments of aerosol direct and indirect forcing. Stratiform cloud water and droplet number are simulated using a bulk microphysics parameterization that includes aerosol activation. Aerosol and trace gas species simulated by MIRAGE are presented and evaluated using surface and aircraft measurements. Surface-level SO2 in N. American and European source regions is higher than observed. SO2 above the boundary layer is in better agreement with observations, and surface-level SO2 at marine locations is somewhat lower than observed. Comparison with other models suggests insufficient SO2 dry deposition; increasing the deposition velocity improves simulated SO2. Surface-level sulfate in N. American and European source regions is in good agreement with observations, although the seasonal cycle in Europe is stronger than observed. Surface-level sulfate at high-latitude and marine locations, and sulfate above the boundary layer, are higher than observed. This is attributed primarily to insufficient wet removal; increasing the wet removal improves simulated sulfate at remote locations and aloft. Because of the high sulfate bias, radiative forcing estimates for anthropogenic sulfur in Ghan et al. [2001c] are probably too high. Surface-level DMS is {approx}40% higher than observed, and the seasonal cycle shows too much DMS in winter, partially caused by neglect of oxidation by NO3. Surface-level MSA at marine locations is {approx}80% higher than observed, also attributed to insufficient wet removal. Surface-level BC is {approx}50% lower than observed in the U.S., and {approx}40% lower than observed globally. Treating BC as initially hydrophobic would lessen this bias. Surface-level organic matter is lower than observed in the U.S., similar to BC, but shows no bias in the global comparison. Surface-level sea salt concentrations are {approx}30% lower than observed, partly caused by low temporal variance of the model's 10 m wind speeds. Submicrometer sea salt is strongly underestimated by the emissions parameterization. Dust concentrations are within a factor of 3 at most sites, but tend to be lower than observed, due primarily to neglect of very large particles and underestimation of emissions and vertical transport under high-wind conditions. Accumulation and Aitken mode number concentrations and mean sizes at the surface over ocean, and condensation nuclei concentrations aloft over the Pacific, are in fair agreement with observations. Concentrations over land are generally higher than observations, with mean sizes correspondingly lower than observations, especially at some European locations. Increasing the assumed size of emitted particles produces better agreement at the surface over land, and reducing the particle nucleation rate improves the agreement aloft over land.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15011821
- Report Number(s):
- PNWD-SA-5826; TRN: US200508%%221
- Journal Information:
- Journal of Geophysical Research. D. (Atmospheres), Vol. 109, Issue D20; Other Information: PBD: 27 Oct 2004
- Country of Publication:
- United States
- Language:
- English
Similar Records
The potential role of methanesulfonic acid (MSA) in aerosol formation and growth and the associated radiative forcings
MATRIX (Multiconfiguration Aerosol TRacker of mIXing state): an aerosol microphysical module for global atmospheric models