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Abstract. This paper describes version 2.0 of the Global Change and Air Pollution (GCAP 2.0) model framework, a one-way offline coupling between version E2.1 of the NASA Goddard Institute for Space Studies (GISS) general circulation model (GCM) and the GEOS-Chem global 3-D chemical-transport model (CTM). Meteorology for driving GEOS-Chem has been archived from the E2.1 contributions to phase 6 of the Coupled Model Intercomparison Project (CMIP6) for the pre-industrial era and the recent past. In addition, meteorology is available for the near future and end of the century for seven future scenarios ranging from extreme mitigation to extreme warming. Emissions and boundary conditions have been prepared for input to GEOS-Chem that are consistent with the CMIP6 experimental design. The model meteorology, emissions, transport, and chemistry are evaluated in the recent past and found to be largely consistent with GEOS-Chem driven by the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) product and with observational constraints. 

Abstract. Emissions are a central component of atmosphericchemistry models. The Harmonized Emissions Component (HEMCO) is a softwarecomponent for computing emissions from a user-selected ensemble of emissioninventories and algorithms. It allows users to re-grid, combine, overwrite,subset, and scale emissions from different inventories through aconfiguration file and with no change to the model source code. Theconfiguration file also maps emissions to model species with appropriateunits. HEMCO can operate in offline stand-alone mode, but more importantlyit provides an online facility for models to compute emissions at runtime.HEMCO complies with the Earth System Modeling Framework (ESMF) forportability across models. We present a new version here, HEMCO 3.0, thatfeatures an improved three-layer architecture to facilitate implementationinto any atmospheric model and improved capability for calculatingemissions at any model resolution including multiscale and unstructuredgrids. The three-layer architecture of HEMCO 3.0 includes (1) the Data InputLayer that reads the configuration file and accesses the HEMCO library ofemission inventories and other environmental data, (2) the HEMCO Core thatcomputes emissions on the user-selected HEMCO grid, and (3) the ModelInterface Layer that re-grids (if needed) and serves the data to theatmospheric model and also serves model data to the HEMCO Core forcomputing emissions dependent on model state (such as from dust or vegetation). The HEMCO Core is common to the implementation in all models, whilethe Data Input Layer and the Model Interface Layer are adaptable to themodel environment. Default versions of the Data Input Layer and ModelInterface Layer enable straightforward implementation of HEMCO in any simplemodel architecture, and options are available to disable features such asre-gridding that may be done by independent couplers in more complexarchitectures. The HEMCO library of emission inventories and algorithms iscontinuously enriched through user contributions so that new inventoriescan be immediately shared across models. HEMCO can also serve as a generaldata broker for models to process input data not only for emissions but forany gridded environmental datasets. We describe existing implementations ofHEMCO 3.0 in (1) the GEOS-Chem “Classic” chemical transport model withshared-memory infrastructure, (2) the high-performance GEOS-Chem (GCHP)model with distributed-memory architecture, (3) the NASA GEOS Earth SystemModel (GEOS ESM), (4) the Weather Research and Forecasting model withGEOS-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 ForecastSystem (UFS). Implementation of HEMCO in CESM2 contributes to theMulti-Scale Infrastructure for Chemistry and Aerosols (MUSICA) by providinga common emissions infrastructure to support different simulations ofatmospheric chemistry across scales. 

Industrial emissions play a major role in the global methane budget. The Permian basin is thought to be responsible for almost half of the methane emissions from all U.S. oil- and gas-producing regions, but little is known about individual contributors, a prerequisite for mitigation. We use a new class of satellite measurements acquired during several days in 2019 and 2020 to perform the first regional-scale and high-resolution survey of methane sources in the Permian. We find an unexpectedly large number of extreme point sources (37 plumes with emission rates >500 kg hour −1 ), which account for a range between 31 and 53% of the estimated emissions in the sampled area. Our analysis reveals that new facilities are major emitters in the area, often due to inefficient flaring operations (20% of detections). These results put current practices into question and are relevant to guide emission reduction efforts. 

Abstract. Bromine radicals influence global tropospheric chemistryby depleting ozone and by oxidizing elemental mercury and reduced sulfurspecies. Observations typically indicate a 50 % depletion of sea saltaerosol (SSA) bromide relative to seawater composition, implying that SSAdebromination could be the dominant global source of tropospheric bromine.However, it has been difficult to reconcile this large source with therelatively low bromine monoxide (BrO) mixing ratios observed in the marineboundary layer (MBL). Here we present a new mechanistic description of SSAdebromination in the GEOS-Chem global atmospheric chemistry model with adetailed representation of halogen (Cl, Br, and I) chemistry. We show thatobserved levels of SSA debromination can be reproduced in a mannerconsistent with observed BrO mixing ratios. Bromine radical sinks from theHOBr + S(IV) heterogeneous reactions and from ocean emission ofacetaldehyde are critical in moderating tropospheric BrO levels. Theresulting HBr is rapidly taken up by SSA and also deposited. Observations of SSA debromination at southern midlatitudes in summer suggest that modeluptake of HBr by SSA may be too fast. The model provides a successfulsimulation of free-tropospheric BrO in the tropics and midlatitudes in summer,where the bromine radical sink from the HOBr + S(IV) reactions iscompensated for by more efficient HOBr-driven recycling in clouds compared toprevious GEOS-Chem versions. Simulated BrO in the MBL is generally muchhigher in winter than in summer due to a combination of greater SSA emissionand slower conversion of bromine radicals to HBr. An outstanding issue inthe model is the overestimate of free-tropospheric BrO in extratropicalwinter–spring, possibly reflecting an overestimate of the HOBr∕HBr ratiounder these conditions where the dominant HOBr source is hydrolysis ofBrNO₃.

 

Abstract. We present a comprehensive simulation of tropospheric chlorinewithin the GEOS-Chem global 3-D model of oxidant–aerosol–halogen atmosphericchemistry. The simulation includes explicit accounting of chloridemobilization from sea salt aerosol by acid displacement of HCl and by otherheterogeneous processes. Additional small sources of tropospheric chlorine(combustion, organochlorines, transport from stratosphere) are also included.Reactive gas-phase chlorine Cl*, including Cl, ClO, Cl2, BrCl, ICl,HOCl, ClNO3, ClNO2, and minor species, is produced by theHCl+OH reaction and by heterogeneous conversion of sea salt aerosolchloride to BrCl, ClNO2, Cl2, and ICl. The modelsuccessfully simulates the observed mixing ratios of HCl in marine air(highest at northern midlatitudes) and the associated HNO3decrease from acid displacement. It captures the high ClNO2 mixingratios observed in continental surface air at night and attributes thechlorine to HCl volatilized from sea salt aerosol and transported inlandfollowing uptake by fine aerosol. The model successfully simulates thevertical profiles of HCl measured from aircraft, where enhancements in thecontinental boundary layer can again be largely explained by transport inlandof the marine source. It does not reproduce the boundary layer Cl2mixing ratios measured in the WINTER aircraft campaign (1–5 ppt in thedaytime, low at night); the model is too high at night, which could be due touncertainty in the rate of the ClNO2+Cl- reaction, but we haveno explanation for the high observed Cl2 in daytime. The globalmean tropospheric concentration of Cl atoms in the model is 620 cm−3and contributes 1.0 % of the global oxidation of methane, 20 % ofethane, 14 % of propane, and 4 % of methanol. Chlorine chemistryincreases global mean tropospheric BrO by 85 %, mainly through theHOBr+Cl- reaction, and decreases global burdens of troposphericozone by 7 % and OH by 3 % through the associated bromine radicalchemistry. ClNO2 chemistry drives increases in ozone of up to8 ppb over polluted continents in winter.