Ozone predictabilities due to meteorological uncertainties in the Mexico City basin using ensemble forecasts

Abstract

The purpose of the present study is to investigate the sensitivity of ozone (O3)[(O subscript 3)] predictions in the Mexico City Metropolitan Area (MCMA) to meteorological initial uncertainties and planetary boundary layer (PBL) parameterization schemes using state-of-the-art meteorological and photochemical prediction models through ensemble forecasts. The simulated periods (3, 9, 15 and 29 March 2006) represent four typical meteorological episodes ("South-Venting", "O3-North" ["O subscript 3 - North"], "O3-South" ["O subscript 3 - South"]and "Convection-North", respectively) in the Mexico City basin during the MCMA-2006/MILAGRO campaign. Our results demonstrate that the uncertainties in meteorological initial conditions have significant impacts on O3 [O subscript 3] predictions, including peak time O3 [O subscript 3] concentrations ([O3] [O subscript 3]), horizontal and vertical O3 [O subscript 3] distributions, and temporal variations. The ensemble spread of the simulated peak [O3 [O subscript 3]] averaged over the city's ambient monitoring sites can reach up to 10 ppb. The increasing uncertainties in meteorological fields during peak O3 [O subscript 3] period contribute to the largest unpredictability in O3 [O subscript 3] simulations, while the impacts of wind speeds and PBL height on [O3 [O subscript 3]] are more straightforward and important. The magnitude of the ensemble spreads varies with different PBL schemes and meteorological episodes. The uncertainties in O3 [O subscript 3] predictions caused by PBL schemes mainly come from their ability to represent the mixing layer height; but overall, these uncertainties are smaller than those from the uncertainties in meteorological initial conditions.