WRF-Chem

WRF-Chem
Name	WRF-Chem
Title	WRF-Chem
Developer	National Center for Atmospheric Research; NOAA; community contributors
Released	2004
Latest release	4.x (varies by distribution)
Operating system	Linux; Unix; macOS
Programming language	Fortran; C; Python (utilities)
Genre	Atmospheric chemistry transport model; mesoscale numerical weather prediction
License	Open-source; research community licenses

WRF-Chem is a coupled numerical model that simulates atmospheric chemistry and aerosol processes within the Weather Research and Forecasting framework. It integrates reactive trace gas chemistry, aerosol microphysics, and feedbacks between chemistry, aerosols, and meteorology to support research linking air quality, weather, and climate. Developed by a consortium including the National Center for Atmospheric Research, NOAA, and academic institutions, it is used worldwide for forecasting, process studies, and policy-relevant assessments.

Overview

WRF-Chem embeds chemical transport and aerosol modules into the mesoscale dynamical core of the Weather Research and Forecasting Model, enabling one-way and two-way interactions among dynamics, radiation, and microphysics. The model supports regional and quasi-global domains over applications such as urban air quality episodes, wildfire smoke, and dust storms. Its design facilitates use with observational networks like AERONET, AirNow, and satellite missions such as MODIS and TROPOMI for diagnostic studies and data assimilation. WRF-Chem has been applied in operational contexts at agencies including NOAA and research centers at NCAR and universities such as Massachusetts Institute of Technology, University of California, Irvine, and Peking University.

Model Components

Major components include the dynamical core from the WRF Model, chemical mechanism libraries, aerosol schemes, emissions processing, and diagnostic tools. The meteorology core interacts with parameterizations such as the Yonsei University (YSU) PBL scheme, Mellor–Yamada–Nakanishi–Niino (MYNN), cumulus schemes like Kain–Fritsch, and radiation packages used in operational suites at ECMWF and NOAA. Chemistry modules leverage solvers and process rate libraries developed collaboratively across institutions like EPA research groups and academic laboratories at University of Washington and Carnegie Mellon University. I/O and pre/post-processing are commonly handled with tools like NetCDF utilities and visualization via NCAR Command Language and Python libraries.

Chemistry and Aerosol Mechanisms

WRF-Chem implements multiple gas-phase chemical mechanisms—ranging from reduced mechanisms used in forecasting to detailed mechanisms for research—including mechanisms developed by groups at University of California, Berkeley, California Institute of Technology, and Scripps Institution of Oceanography. Aerosol treatments span bulk to sectional and modal approaches, with modules derived from studies at Aerodyne Research, Max Planck Institute for Chemistry, and Laboratoire de Météorologie Dynamique. Processes modeled include gas-aerosol partitioning, heterogeneous chemistry on aerosol surfaces, secondary organic aerosol formation, and size-resolved coagulation and deposition parameterizations grounded in literature from Harvard University and ETH Zurich.

Emissions and Input Data

Emission inputs combine anthropogenic inventories like EDGAR (Emissions Database for Global Atmospheric Research), NEI (National Emissions Inventory), and regional datasets maintained by agencies such as EPA and European Environment Agency, with biogenic emission models developed at NOAA/ESRL and Colorado State University. Fire emissions are ingested from products such as GFED and operational systems built around MODIS fire detections used by NASA centers. Dust and sea-salt flux parameterizations are informed by climatologies from institutions like USGS and NOAA/NESDIS. Land-surface and boundary conditions often derive from reanalysis datasets at NCEP and ECMWF and from chemistry boundary datasets produced for intercomparison exercises organized by GEIA and international modeling consortia.

Coupling and Physics Integration

The coupled framework permits direct feedbacks whereby aerosols modify radiation, cloud microphysics, and surface energy budgets, affecting circulations that in turn influence chemistry. Coupling strategies mirror approaches used in Earth system models like those at NCAR CESM and GFDL, enabling aerosol–radiation and aerosol–cloud interactions alongside wet and dry deposition processes. Integration with convective parameterizations such as Kain–Fritsch and cloud microphysics like Thompson microphysics allows simulations of scavenging and aqueous-phase chemistry that are crucial for representing episode evolution in regions studied by teams at University of Iowa and Texas A&M University.

Applications and Case Studies

Applications include urban air quality forecasting for metropolitan areas like Los Angeles, Beijing, and Delhi, smoke dispersion and air quality impacts of wildfires in the Western United States, transboundary dust events from the Sahara and Gobi Desert, and volcanic plume chemistry following eruptions monitored by observatories such as USGS Volcano Hazards Program. WRF-Chem has supported field campaigns run by organizations like ARM (Atmospheric Radiation Measurement) and INTEX, and contributed to intercomparison projects coordinated by AQMEII and HTAP.

Evaluation and Performance

Model evaluation uses surface networks (e.g., AirNow, European Air Quality Index stations), remote sensing such as AERONET and satellite aerosol optical depth products from MODIS and VIIRS, and aircraft campaign datasets from NASA and NOAA. Performance metrics focus on concentration biases, diurnal cycles, and aerosol optical properties compared against reference measurements curated by labs at NOAA/ESRL and academic groups at Columbia University and Imperial College London. Computational performance depends on resolution and mechanism complexity, with parallel scalability tested on supercomputing centers like NCAR, NERSC, and XSEDE facilities.

Development and Community

WRF-Chem development is stewarded through collaborative workflows involving NCAR, NOAA, university groups, and international users; code contributions and issue tracking occur within community repositories and workshops hosted by institutions such as NCAR and NOAA ESRL. Training and user support are provided via tutorials at conferences like the American Geophysical Union Fall Meeting and workshops organized by AMS (American Meteorological Society). Ongoing research priorities include improved representation of secondary organic aerosols, ammonia–aerosol interactions studied at Max Planck Institute for Meteorology, and coupling to chemistry–climate frameworks led by groups at IPCC-contributing institutions.

Category:Atmospheric chemistry models