Harmonized Emissions Component (HEMCO) 3.0 as a versatile emissions component for atmospheric models: application in the GEOS-Chem, NASA GEOS, WRF-GC, CESM2, NOAA GEFS-Aerosol, and NOAA UFS models
Authors: Lin Haipeng , Jacob Daniel J. , Lundgren Elizabeth W. , Sulprizio Melissa P. , Keller Christoph A. , Fritz Thibaud M. , Eastham Sebastian D. , Emmons Louisa K. , Campbell Patrick C. , Baker Barry , Saylor Rick D. , Montuoro Raffaele 
Published: September 2021

Abstract. Emissions are a central component of atmospheric
chemistry models. The Harmonized Emissions Component (HEMCO) is a software
component for computing emissions from a user-selected ensemble of emission
inventories and algorithms. It allows users to re-grid, combine, overwrite,
subset, and scale emissions from different inventories through a
configuration file and with no change to the model source code. The
configuration file also maps emissions to model species with appropriate
units. HEMCO can operate in offline stand-alone mode, but more importantly
it provides an online facility for models to compute emissions at runtime.
HEMCO complies with the Earth System Modeling Framework (ESMF) for
portability across models. We present a new version here, HEMCO 3.0, that
features an improved three-layer architecture to facilitate implementation
into any atmospheric model and improved capability for calculating
emissions at any model resolution including multiscale and unstructured
grids. The three-layer architecture of HEMCO 3.0 includes (1) the Data Input
Layer that reads the configuration file and accesses the HEMCO library of
emission inventories and other environmental data, (2) the HEMCO Core that
computes emissions on the user-selected HEMCO grid, and (3) the Model
Interface Layer that re-grids (if needed) and serves the data to the
atmospheric model and also serves model data to the HEMCO Core for
computing emissions dependent on model state (such as from dust or vegetation). The HEMCO Core is common to the implementation in all models, while
the Data Input Layer and the Model Interface Layer are adaptable to the
model environment. Default versions of the Data Input Layer and Model
Interface Layer enable straightforward implementation of HEMCO in any simple
model architecture, and options are available to disable features such as
re-gridding that may be done by independent couplers in more complex
architectures. The HEMCO library of emission inventories and algorithms is
continuously enriched through user contributions so that new inventories
can be immediately shared across models. HEMCO can also serve as a general
data broker for models to process input data not only for emissions but for
any gridded environmental datasets. We describe existing implementations of
HEMCO 3.0 in (1) the GEOS-Chem “Classic” chemical transport model with
shared-memory infrastructure, (2) the high-performance GEOS-Chem (GCHP)
model with distributed-memory architecture, (3) the NASA GEOS Earth System
Model (GEOS ESM), (4) the Weather Research and Forecasting model with
GEOS-Chem (WRF-GC), (5) the Community Earth System Model Version 2 (CESM2),
and (6) the NOAA Global Ensemble Forecast System – Aerosols
(GEFS-Aerosols), as well as the planned implementation in the NOAA Unified Forecast
System (UFS). Implementation of HEMCO in CESM2 contributes to the
Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA) by providing
a common emissions infrastructure to support different simulations of
atmospheric chemistry across scales.