Abstract
The Community Multiscale Air Quality (CMAQ) modeling system is extended to simulate ozone, particulate matter, and related precursor distributions throughout the Northern Hemisphere. Modelled processes were examined and enhanced to suitably represent the extended space and time scales for such applications. Hemispheric scale simulations with CMAQ and the Weather Research and Forecasting (WRF) model are performed for multiple years. Model capabilities for a range of applications including episodic long-range pollutant transport, long-term trends in air pollution across the Northern Hemisphere, and air pollution-climate interactions are evaluated through detailed comparison with available surface, aloft, and remotely sensed observations. The expansion of CMAQ to simulate the hemispheric scales provides a framework to examine interactions between atmospheric processes occurring at various spatial and temporal scales with physical, chemical, and dynamical consistency.
Highlights
Comprehensive atmospheric chemistry transport models must constantly evolve to address the increasing complexity arising from emerging applications that treat multi-pollutant interactions on urban to hemispheric spatial scales and hourly to annual temporal scales
Though significant seasonal variability is noted in the free troposphere (FT) fractional contributions to surface-level background concentrations, the contributions are still substantial during other seasons and expectedly the highest contributions are seen in the high-elevation regions of the western United States across all seasons
To overcome some of these challenges and to develop a more robust representation of stratosphere–troposphere exchange (STE) impacts, we have recently developed a dynamic O3–potential vorticity (PV) function based on 21year ozonesonde records from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) with corresponding PV values from Weather Research and Forecasting (WRF)-Community Multiscale Air Quality (CMAQ) simulation across the Northern Hemisphere from 1990 to 2010
Summary
Based on typical advective timescales, it can further be postulated that in limited-area chemistry transport models, this free-tropospheric variability in simulated concentrations is largely dictated by the specification of lateral boundary conditions (LBCs) This is exemplified, which illustrates the influence of LBC specification on simulated surface-level concentrations across a typical regional modeling domain covering the contiguous United States; the spaceand time-varying LBCs themselves were derived from the global Integrated Forecasting System of the European Center for Medium-Range Weather Forecasts (ECMWF) (Flemming et al, 2015). Though significant seasonal variability is noted in the FT fractional contributions to surface-level background concentrations, the contributions are still substantial during other seasons and expectedly the highest contributions are seen in the high-elevation regions of the western United States across all seasons These results clearly illustrate the importance of accurately characterizing the long-range transport that occurs in the FT and its influence on surface background pollution levels via subsidence and entrainment into the BL.
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