A Short Description of the NOAA HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) Model

Xin-Zhong Liang
University of Illinois at Urbana-Champaign,
Champaign, IL USA

A state-of-the-art integrated modeling system has been developed and applied to quantify the individual and combined impacts of global climate and emission changes on U.S. air quality at regional to local scales, from the present to 2050 and 2100. Simulations from two global general circulation models (GCMs) under the IPCC SRES A1Fi, B1, A2, B2 emissions scenarios are used to drive the regional modeling system that produce downscaling of the U.S. present climate, future change and their impacts on air quality as well as the uncertainty of the results. It is shown that the dynamic downscaling can significantly reduce biases of the driving global models in simulating the present climate/air quality patterns and that this improvement has important consequences for future projections of regional climate/air quality changes. For both the present and future climate simulations, the regional modeling system results are sensitive to the planetary forcings imposed by outputs from different global models as well as to its own physical process representations, especially different cumulus parameterizations, with strong regional dependence. Due to these sensitivities, there are large uncertainties involved in application of model projections of future climate/air quality changes for decision making at regional to local scales. Given significant uncertainties in estimating/projecting surface emissions and important contributions from long-range pollutant transport, decision making on future U.S. air quality regulation is challenging.