A reduced form metamodel has been produced to simulate the effects ofphysical, chemical, and meteorological processing of highly reactive tracespecies in urban areas, which is capable of efficiently simulating the urbanconcentration, surface deposition, and net export flux of these species. Apolynomial chaos expansion and the probabilistic collocation method have beenused to develop the metamodel, and its coefficients, so that it is applicableunder a broad range of present-day and future conditions. The inputs uponwhich this metamodel have been formed are based on a combination of physicalproperties (average temperature, diurnal temperature range, date, andlatitude), anthropogenic properties (patterns and amounts of emissions), andthe nature of the surrounding environment (background concentrations ofspecies). The metamodel development involved using probability distributionfunctions (PDFs) of the inputs to run a detailed parent chemical and physicalmodel, the Comprehensive Air Quality Model with Extensions (CAMx), thousandsof times. Outputs from these runs were used in turn to both determine thecoefficients of and test the precision of the metamodel, as compared with thedetailed parent model. It was determined that the deviations between themetamodel and the parent mode for many important species (O, CO, NO,and black carbon (BC)) were found to have a weighted RMS error less than10 % in all cases, with many of the specific cases having a weighted RMSerror less than 1 %. Some of the other important species (VOCs, PAN, OC,and sulfate aerosol) usually have their weighted RMS error less than 10 %as well, except for a small number of cases. In these cases, the complexityand non-linearity of the physical, chemical, and meteorological processing istoo large for the third order metamodel to give an accurate fit. Finally,sensitivity tests have been performed, to observe the response of the 16metamodels (4 different meteorologies and 4 different urban types) to a broadset of potential inputs. These results were compared with observations ofozone, CO, formaldehyde, BC, and PM from a few well observed urbanareas, and in most of the cases, the output distributions were found to bewithin ranges of the observations. Overall, a set of efficient and robustmetamodels have been generated which are capable of simulating the effects ofvarious physical, chemical, and meteorological processing, and capable ofdetermining the urban concentrations, mole fractions, and fluxes of species,important to human health and the global climate.
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