A pathway analysis of global aerosol processes

Schutgens, Nick; Stier, Philip

doi:10.5194/acp-14-11657-2014

Cited by 36 publications

(39 citation statements)

References 74 publications

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“…More details and an extensive evaluation of this base model can be found in (Stier et al, 2005Zhang et al, 2012;Schutgens and Stier, 2014) as well as part of the AeroCom intercomparison Stier et al, 2013;Mann et al, 2014).…”

Section: Methodsmentioning

confidence: 99%

Limitations of passive remote sensing to constrain global cloud condensation nuclei

2016

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Abstract. Aerosol-cloud interactions are considered a key uncertainty in our understanding of climate change . Knowledge of the global abundance of cloud condensation nuclei (CCN) is fundamental to determine the strength of the anthropogenic climate perturbation. Direct measurements are limited and sample only a very small fraction of the globe so that remote sensing from satellites and ground-based instruments is widely used as a proxy for cloud condensation nuclei (Nakajima et al., 2001;Andreae, 2009;Clarke and Kapustin, 2010;Boucher et al., 2013). However, the underlying assumptions cannot be robustly tested with the small number of measurements available so that no reliable global estimate of cloud condensation nuclei exists. This study overcomes this limitation using a self-consistent global model (ECHAM-HAM) of aerosol radiative properties and cloud condensation nuclei. An analysis of the correlation of simulated aerosol radiative properties and cloud condensation nuclei reveals that common assumptions about their relationships are violated for a significant fraction of the globe: 71 % of the area of the globe shows correlation coefficients between CCN 0.2 % at cloud base and aerosol optical depth (AOD) below 0.5, i.e. AOD variability explains only 25 % of the CCN variance. This has significant implications for satellite based studies of aerosol-cloud interactions. The findings also suggest that vertically resolved remote-sensing techniques, such as satellite-based high spectral resolution lidars, have a large potential for global monitoring of cloud condensation nuclei.

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Section: Methodsmentioning

confidence: 99%

Limitations of passive remote sensing to constrain global cloud condensation nuclei

2016

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“…At the global scale, and knowing the importance of the aerosol load and composition on Earth's climate, models were significantly improved and were able to accurately describe the different steps in the aerosol formation using complex schemes for nucleation, condensation and coagulation (Schutgens and Stier, 2014). These global models are compared and their strength and weakness are quantified, as, for example, in Huneeus et al (2011) for the mineral dust emissions, transport and deposition in the framework of the AEROCOM project.…”

Section: Menut Et Al: Aerosol Speciation and Size Distributionmentioning

confidence: 99%

Observations and regional modeling of aerosol optical properties, speciation and size distribution over Northern Africa and western Europe

et al. 2016

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Abstract. The aerosol speciation and size distribution is modeled during the summer 2013 and over a large area encompassing Africa, Mediterranean and western Europe. The modeled aerosol is compared to available measurements such as the AERONET aerosol optical depth (AOD) and aerosol size distribution (ASD) and the EMEP network for surface concentrations of particulate matter PM 2.5 , PM 10 and inorganic species (nitrate, sulfate and ammonium). The main goal of this study is to quantify the model ability to realistically model the speciation and size distribution of the aerosol. Results first showed that the long-range transport pathways are well reproduced and mainly constituted by mineral dust: spatial correlation is ≈ 0.9 for AOD and Ångström exponent, when temporal correlations show that the day-to-day variability is more difficult to reproduce. Over Europe, PM 2.5 and PM 10 have a mean temporal correlation of ≈ 0.4 but the lowest spatial correlation (≈ 0.25 and 0.62, respectively), showing that the fine particles are not well localized or transported. Being short-lived species, the uncertainties on meteorology and emissions induce these lowest scores. However, time series of PM 2.5 with the speciation show a good agreement between model and measurements and are useful for discriminating the aerosol composition. Using a classification from the south (Africa) to the north (northern Europe), it is shown that mineral dust relative mass contribution decreases from 50 to 10 % when nitrate increases from 0 to 20 % and all other species, sulfate, sea salt, ammonium, elemental carbon, primary organic matter, are constant. The secondary organic aerosol contribution is between 10 and 20 % with a maximum at the latitude of the Mediterranean Sea (Spanish stations). For inorganic species, it is shown that nitrate, sulfate and ammonium have a mean temporal correlation of 0.25, 0.37 and 0.17, respectively. The spatial correlation is better (0.25, 0.5 and 0.87), showing that the mean values may be biased but the spatial localization of sulfate and ammonium is well reproduced. The size distribution is compared to the AERONET product and it is shown that the model fairly reproduces the main values for the fine and coarse mode. In particular, for the fine mode, the model overestimates the aerosol mass in Africa and underestimates it in Europe.

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“…For details on the implementation of sedimentation, wet and dry deposition, thermodynamics and aerosol micro-physics parametrization, see Stier et al (2005). A detailed assessment of the processes which drive the evolution of aerosol mass and number concentrations is described in Schutgens and Stier (2014). Calculations of aerosol optical properties are based on Mie theory for 24 solar spectral bands and provide single scattering albedo, extinction cross section and asymmetry factors.…”

Section: Echam6-ham2mentioning

confidence: 99%

Fire emission heights in the climate system – Part 2: Impact on transport, black carbon concentrations and radiation

et al. 2015

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Abstract. Wildfires represent a major source for aerosols impacting atmospheric radiation, atmospheric chemistry and cloud micro-physical properties. Previous case studies indicated that the height of the aerosol-radiation interaction may crucially affect atmospheric radiation, but the sensitivity to emission heights has been examined with only a few models and is still uncertain. In this study we use the general circulation model ECHAM6 extended by the aerosol module HAM2 to investigate the impact of wildfire emission heights on atmospheric long-range transport, black carbon (BC) concentrations and atmospheric radiation. We simulate the wildfire aerosol release using either various versions of a semiempirical plume height parametrization or prescribed standard emission heights in ECHAM6-HAM2. Extreme scenarios of near-surface or free-tropospheric-only injections provide lower and upper constraints on the emission height climate impact. We find relative changes in mean global atmospheric BC burden of up to 7.9 ± 4.4 % caused by average changes in emission heights of 1.5-3.5 km. Regionally, changes in BC burden exceed 30-40 % in the major biomass burning regions. The model evaluation of aerosol optical thickness (AOT) against Moderate Resolution Imaging Spectroradiometer (MODIS), AErosol RObotic NETwork (AERONET) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations indicates that the implementation of a plume height parametrization slightly reduces the ECHAM6-HAM2 biases regionally, but on the global scale these improvements in model performance are small. For prescribed emission release at the surface, wildfire emissions entail a total sky top-of-atmosphere (TOA) radiative forcing (RF) of −0.16 ± 0.06 W m −2 . The application of a plume height parametrization which agrees reasonably well with observations introduces a slightly stronger negative TOA RF of −0.20 ± 0.07 W m −2 . The standard ECHAM6-HAM2 model in which 25 % of the wildfire emissions are injected into the free troposphere (FT) and 75 % into the planetary boundary layer (PBL), leads to a TOA RF of −0.24 ± 0.06 W m −2 . Overall, we conclude that simple plume height parametrizations provide sufficient representations of emission heights for global climate modeling. Significant improvements in aerosol wildfire modeling likely depend on better emission inventories and aerosol process modeling rather than on improved emission height parametrizations.

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A pathway analysis of global aerosol processes

Cited by 36 publications

References 74 publications

Limitations of passive remote sensing to constrain global cloud condensation nuclei

Limitations of passive remote sensing to constrain global cloud condensation nuclei

Observations and regional modeling of aerosol optical properties, speciation and size distribution over Northern Africa and western Europe

Fire emission heights in the climate system – Part 2: Impact on transport, black carbon concentrations and radiation

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