Ensuring Mass Consistency Between Meteorological and Air Quality Models

Friday, March 17, 2000 - 4:30pm - 5:00pm
Keller 3-180
Ralph Morris (ENVIRON Corporation)
Joint work with Chris Emery.

Over the past decade there has been a movement toward using more advanced prognostic meteorological models (e.g., MM5 and RAMS) for developing meteorological inputs for regional air quality models. A key component of this meshing is to ensure mass consistency between the two models. To accomplish this, the meteorological and air quality models are now frequently applied with the same horizontal grid system and vertical layer structure (although typically air quality models may combine some vertical layers together). However, even using an identical grid structure and a meteorological model that produces perfectly mass consistent (u, v, w) wind fields does not guarantee that the air quality model will be mass consistent because different numerical solution schemes are used to solve the transport equations. That is, the vertical velocity (w) that achieves mass consistency in the air quality model depends on the numerical solution to the horizontal (u, v) transport; different numerical solutions schemes will require different vertical velocities to achieve mass consistency. For the CAMx model, mass consistency is achieved by preserving the local air density in a mass consistent fashion. This technique is described, and examples presented for MM5/CAMx and RAMS/CAMx simulations in the Lake Michigan lake-breeze and eastern U.S. complex terrain and sea breeze environments. Mass consistency simulations are performed by specifying a unit mixing ratio for initial and boundary conditions and analyzing any deviations from unity.