Modelling of primary aerosols in the chemical transport model MOCAGE: development and evaluation of aerosol physical parameterizations

Abstract

Abstract. This paper deals with recent improvements to the global chemical transport model of Météo-France MOCAGE (Modèle de Chimie Atmosphérique à Grande Echelle) that consists of updates to different aerosol parameterizations. MOCAGE only contains primary aerosol species: desert dust, sea salt, black carbon, organic carbon, and also volcanic ash in the case of large volcanic eruptions. We introduced important changes to the aerosol parameterization concerning emissions, wet deposition and sedimentation. For the emissions, size distribution and wind calculations are modified for desert dust aerosols, and a surface sea temperature dependant source function is introduced for sea salt aerosols. Wet deposition is modified toward a more physically realistic representation by introducing re-evaporation of falling rain and snowfall scavenging and by changing the in-cloud scavenging scheme along with calculations of precipitation cloud cover and rain properties. The sedimentation scheme update includes changes regarding the stability and viscosity calculations. Independent data from satellites (MODIS, SEVIRI), the ground (AERONET, EMEP), and a model inter-comparison project (AeroCom) are compared with MOCAGE simulations and show that the introduced changes brought a significant improvement on aerosol representation, properties and global distribution. Emitted quantities of desert dust and sea salt, as well their lifetimes, moved closer towards values of AeroCom estimates and the multimodel average. When comparing the model simulations with MODIS aerosol optical depth (AOD) observations over the oceans, the updated model configuration shows a decrease in the modified normalized mean bias (MNMB; from 0.42 to 0.10) and a better correlation (from 0.06 to 0.32) in terms of the geographical distribution and the temporal variability. The updates corrected a strong positive MNMB in the sea salt representation at high latitudes (from 0.65 to 0.16), and a negative MNMB in the desert dust representation in the African dust outflow region (from − 1.01 to −0.22). The updates in sedimentation produced a modest difference; the MNMB with MODIS data from 0.10 in the updated configuration went to 0.11 in the updated configuration only without the sedimentation updates. Yet, the updates in the emissions and the wet deposition made a stronger impact on the results; the MNMB was 0.27 and 0.21 in updated configurations only without emission, and only without wet deposition updates, respectively. Also, the lifetime, the extent, and the strength of the episodic aerosol events are better reproduced in the updated configuration. The wet deposition processes and the differences between the various configurations that were tested greatly influence the representation of the episodic events. However, wet deposition is not a continuous process; it has a local and episodic signature and its representation depends strongly on the precipitation regime in the model.

Aerosol data assimilation in the chemical transport model MOCAGE during the TRAQA/ChArMEx campaign: aerosol optical depth

“…It serves as an operational air quality model and simulates gases (Josse et al, 2004;Dufour et al, 2005) and primary (directly emitted) aerosols (Martet et al, 2009;Sič et al, 2015). It transports atmospheric species by a semi-Lagrangian advection scheme (Williamson and Rasch, 1989).…”

“…As a consequence, efforts to accurately represent aerosols in models also increased (for example Kanakidou et al, 2005;Textor et al, 2006;Fuzzi et al, 2006;Vignati et al, 2010;Lee et al, 2011;Boucher et al, 2013;Sič et al, 2015). The development of aerosol modelling enables us to better understand how aerosols affect atmospheric chemistry, air quality, climate, aviation, visibility, radiative budget and clouds.…”

“…Josse et al, 2004;Sič et al, 2015, Modèle de Chimie Atmosphérique à Grande Echelle). Our goal is to assimilate the regular daily global mapping of the 2-D column AOD by the National Aeronautics and Space Administration (NASA) Terra and Aqua satellites (Remer et al, 2005) with the 3-D CTM modelling of the major tropospheric aerosols.…”

Intercontinental transport of biomass burning pollutants over the Mediterranean Basin during the summer 2014 ChArMEx-GLAM airborne campaign

“…MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle; Josse et al, 2004;Sič et al, 2015;Guth et al, 2016) is used in this study to simulate the CO global atmospheric content in order to trace the biomass burning events. MOCAGE is a 3D stratospheric and tropospheric Chemistry Transport Model (CTM) using a semi-…”

“…carbon monoxide, CO and nitrogen oxides, NO x ) that impact the composition of the atmosphere at regional and global scales, with consequences on ozone (O 3 ) formation. CO, a tracer for biomass burning emissions produced from incomplete combustion, is a precursor of tropospheric O 3 and a sink for radical hydroxyl (OH), the main oxidising species in the atmosphere 40 (Seinfeld and Pandis, 2016). Forest fires are also an important source of tropospheric aerosols that play a significant role on radiative properties of the atmosphere (Liousse et al, 1996) especially in the Mediterranean region (Pace et al, 2005;Bougiatioti et al, 2016).…”