1Atmospheric Sciences Research Center, State University of New York at Albany, Albany, NY, USA
2New York State Department of Environmental Conservation, Albany, NY, USA
3Weather It Is, LTD, Efrat, Israel
4NASA-Goddard Institute for Space Studies, New York, NY, USA
5Forschungszentrum Jülich, Germany
6Max Planck Institute for Meteorology, Hamburg, Germany
7University of Alabama, Huntsville, AL, USA
8Mailman School of Public Health, Columbia University, New York, NY, USA
Received: 31 Aug 2010 – Discussion started: 06 Oct 2010
Abstract. This study presents the results from two sets of 18-year air quality simulations over the Northeastern US performed with a regional photochemical modeling system. These two simulations utilize different sets of lateral boundary conditions, one corresponding to a time-invariant climatological vertical profile and the other derived from monthly mean concentrations extracted from archived ECHAM5-MOZART global simulations. The objective is to provide illustrative examples of how model performance in several key aspects – trends, intra- and interannual variability of ground-level ozone, and ozone/precursor relationships – can be evaluated against available observations, and to identify key inputs and processes that need to be considered when performing and improving such long-term simulations. To this end, several methods for comparing observed and simulated trends and variability of ground level ozone concentrations, ozone precursors and ozone/precursor relationships are introduced. The application of these methods to the simulation using time-invariant boundary conditions reveals that the observed downward trend in the upper percentiles of summertime ozone concentrations is captured by the model in both directionality and magnitude. However, for lower percentiles there is a marked disagreement between observed and simulated trends. In terms of variability, the simulations using the time-invariant boundary conditions underestimate observed inter-annual variability by 30%–50% depending on the percentiles of the distribution. The use of boundary conditions from the ECHAM5-MOZART simulations improves the representation of interannual variability but has an adverse impact on the simulated ozone trends. Moreover, biases in the global simulations have the potential to significantly affect ozone simulations throughout the modeling domain, both at the surface and aloft. The comparison of both simulations highlights the significant impact lateral boundary conditions can have on a regional air quality model's ability to simulate long-term ozone variability and trends, especially for the lower percentiles of the ozone distribution.
Revised: 22 Dec 2010 – Accepted: 05 Jan 2011 – Published: 20 Jan 2011
Hogrefe, C., Hao, W., Zalewsky, E. E., Ku, J.-Y., Lynn, B., Rosenzweig, C., Schultz, M. G., Rast, S., Newchurch, M. J., Wang, L., Kinney, P. L., and Sistla, G.: An analysis of long-term regional-scale ozone simulations over the Northeastern United States: variability and trends, Atmos. Chem. Phys., 11, 567-582, doi:10.5194/acp-11-567-2011, 2011.