Evaluation of black carbon estimations in global aerosol models

Abstract

Abstract. We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) from AERONET and Ozone Monitoring Instrument (OMI) retrievals and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.6 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50 N, the average model is a factor of 10 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC is 0.6 and underestimates the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

“…Additionally we have included two sensitivity simulations that have the in-cloud impaction processes turned off for both the diagnostic and prognostic in-cloud scavenging schemes, DIAG-FULL-noimp and PROG-AP-noimp, respectively. Figure 14 shows profiles from the tropics and midlatitudes taken between the equator, and 50 • N and between 120 • E and 60 • E and averaged for the same points as shown in Koch et al ( , 2010. Figure 15 presents profiles from the high latitudes taken between 50 • N and 80 • N and between 180 • E and 60 • E and averaged for the same points as shown in Koch et al ( , 2010.…”

“…Figure 14 shows profiles from the tropics and midlatitudes taken between the equator, and 50 • N and between 120 • E and 60 • E and averaged for the same points as shown in Koch et al ( , 2010. Figure 15 presents profiles from the high latitudes taken between 50 • N and 80 • N and between 180 • E and 60 • E and averaged for the same points as shown in Koch et al ( , 2010. These figures show that the predicted black carbon profiles, particularly in the middle troposphere differ from the observations, and between each other, by up to two orders of magnitude depending on the treatment of in-cloud scavenging.…”

Aerosol optical depth over the Arctic: a comparison of ECHAM-HAM and TM5 with ground-based, satellite and reanalysis data

“…While ACCMIP includes data from the Global Fire Emission Database 2 (GFED2), we also explore ACCMIP emissions using the more recent GFED3 monthly biomass burning emission database (van der Werf et al, 2010) and we allow these emissions (sulfur, black carbon and organic matter) to vary annually instead of using a climatological mean. Koch and Hansen (2005) showed that, while the largest contribution in terms of sulfate aerosols to Arctic AOD comes from Russia, South-East Asia contributes with a significant fraction. Since there is a significant difference in terms of sulfate emissions between the REAS and AC-CMIP emission datasets, we explore the possible impact of a change in anthropogenic SO 2 emissions in the SouthEast Asia region.…”

“…(Law and Stohl, 2007;Stohl, 2006;Stocks et al, 1998;Koch and Hansen, 2005), with important interannual variability, the choice of biomass burning emissions datasets may play an important role. Variability in these emissions, interacting with interannual changes in circulation, may lead to significant changes in Arctic aerosol concentrations.…”

“…The source areas for nearly all air pollutants in the Arctic are believed to be in mid latitudes (Law and Stohl, 2007), but the presence of transport barriers and complex removal processes leads to a difficult identification of the transport pathways, which has advanced only recently (see, e.g., Koch and Hansen, 2005;Stohl, 2006;Shindell et al, 2008;Hirdman et al, 2010a,b;Huang et al, 2010;Bourgeois and Bey, 2011).…”