Environmental Engineering Reference
In-Depth Information
Board (CARB). These flights, already configured for the ARCTAS mission, examined
California's atmosphere to better understand the chemical dynamics of smog and
greenhouse gases over the state. During these flights, various organizations produced
both meteorology and air quality forecasts to assist flight-path planning. We will
discuss the accuracy of these forecasts with respect to the large-scale features
observed.
Four science flights were conducted in California during the 18-24 June 2008
period. The two-dimensional flight paths for those flights are shown in
Fig. 1.
The
flights on June 18 and 24 focused on characterizing photochemistry, emissions
and boundary conditions (both inflow and outflow) in southern California. The
flight on June 20 attempted to characterize the photochemistry and emissions in
central California including the Bay Area. Inflow boundary conditions for photo-
chemical modeling were the focus of the June 22nd flight.
A large number of chemical species (both inorganic and organic) were measured
during these flights using various measurement methods. Most of these chemical
species, especially the free radicals, are not measured at routine groundbased
measurement sites. We will demonstrate how these additional measurements are
useful for understanding the chemical regimes of various air parcels.
2. Model Application
The month of June 2008 was simulated using CMAQ v4.6 [4] for a modeling
domain that includes all of California with 4 × 4 km horizontal grid cells and 30
vertical layers. Meteorological inputs were generated from simulations with the
mesoscale meteorological model [5] (MM5) with analysis nudging but without
observational nudging. Emissions were prepared internally at the California Air
Resources Board. The base year for emissions was 2002, and emissions were
projected to 2005 assuming no appreciable emission changes in California
between 2005 and 2008. Gas-phase chemistry was simulated using the SAPRC99
mechanism [6], and aerosol processes were simulated with the AE4 module. We
consider these simulation results to be preliminary. A more rigorous simulation
will be conducted in the near future using emissions projected to 2008 from a
2005 base year, MM5 simulations with observational nudging, and a more
detailed version of the SAPRC99 chemical mechanism that explicitly models
several additional measured species.
We will present a comparison of the results of preliminary meteorology/
airquality modeling with measurements aloft by aircrafts as well as those at the
ground monitoring stations.
