Extending the Community Multiscale Air Quality (CMAQ) modeling system to hemispheric scales: overview of process considerations and initial applications

Abstract

Abstract. The Community Multiscale Air Quality (CMAQ) modeling system is extended to simulate ozone, particulate matter, and related precursor distributions throughout the Northern Hemisphere. Modeled processes were examined and enhanced to suitably represent the extended space and timescales 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 longrange 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 on various spatial and temporal scales with physical, chemical, and dynamical consistency.

Multi-Model Comparison in the Impact of Lateral Boundary Conditions on Simulated Surface Ozone across the United States Using Chemically Inert Tracers

“…Studies based on chemical transport models (CTMs) have shown that air quality in the U.S. can be considerably influenced by pollutants beyond the U.S. boundaries, such as through intercontinental transport, and through stratosphere-totroposphere exchange (Zhang et al, 2011;Lin et al, 2012;Nopmongcol et al, 2016;Langford et al, 2017;Lin et al, 2017;Hogrefe et al, 2017;Mathur et al, 2017). Similar findings have also been reported based on routine observations and field 5 campaign measurements (e.g.…”

Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 – Part 1: Model evaluation and air mass characterization for stratosphere–troposphere transport

“…Thus, model O 3 values in layers between 100 and 50 hPa are scaled to space-and time-varying PV fields. The model dynamics (3-D advection, cloud mixing, and turbulent transport) then transport this O 3 which is nominally representative of stratospheric origin through the modeled troposphere, as detailed in Mathur et al (2017). Based on this new parameterization, it was demonstrated that UTLS O 3 agreed much better with observation in terms of its magnitude and seasonality (Xing et al, 2016).…”

“…3.1), in this work, using a grid resolution of 108 km provides a good compromise between numerical accuracy and computational constraints. The terrain-following vertical coordinate utilizes 44 layers of variable thickness to resolve the model vertical extent between the surface and 50 hPa based on the extension of the previous 35-layer system Mathur et al, 2017). The revised layer structure using 44 layers with significantly finer resolution above the boundary layer (BL) better represents long-range transport in the free troposphere (FT) as well as STT processes, and influences from cloud mixing on both the subgrid and resolved scales.…”

“…The revised layer structure using 44 layers with significantly finer resolution above the boundary layer (BL) better represents long-range transport in the free troposphere (FT) as well as STT processes, and influences from cloud mixing on both the subgrid and resolved scales. As indicated in Mathur et al (2017), the 44-layer configuration employed in the H-CMAQ configuration helps to better capture dynamics in the vicinity of the tropopause and reduce excessive diffusion relative to coarser vertical resolution configurations. The emission inputs are based on the Hemispheric Transport of Air Pollution version 2 (HTAP2) modeling experiments, and a detailed description can be found in previous studies (Janssens-Maenhout et al, 2015;Pouliot et al, 2015;Galmarini et al, 2017;Hogrefe et al, 2018).…”

“…PV shows a strong positive correlation with O 3 (Danielsen, 1968), and modeling studies have used this correlation to develop scaling factors that specify O 3 in the modeled upper tropo-sphere/lower stratosphere (UTLS) based on estimated PV. The reported O 3 /PV ratios exhibited a wide range from 20 to 100 ppbv/PVU depending on location, altitude, and season (e.g., Ebel et al, 1991;Carmichael et al, 1998;McCaffery et al, 2004). To account for the seasonal, latitudinal, and altitude dependencies in the O 3 /PV relationship, a dynamic O 3 /PV function was developed to consider latitude, altitude, and time based on 21-year ozonesonde records from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) and corresponding PV values from WRF-CMAQ simulations across the Northern Hemisphere from 1990 to 2010 and is used in H-CMAQ (Xing et al, 2016).…”