12 research outputs found
Atmospheric processing of iron in mineral and combustion aerosols: development of an intermediate-complexity mechanism suitable for Earth system models
Atmospheric processing of iron in dust and combustion aerosols is simulated using an intermediate-complexity soluble iron mechanism designed for Earth system models. The solubilization mechanism includes both a dependence on aerosol water pH and in-cloud oxalic acid. The simulations of size-resolved total, soluble and fractional iron solubility indicate that this mechanism captures many but not all of the features seen from cruise observations of labile iron. The primary objective was to determine the extent to which our solubility scheme could adequately match observations of fractional iron solubility. We define a semi-quantitative metric as the model mean at points with observations divided by the observational mean (MMO). The model is in reasonable agreement with observations of fractional iron solubility with an MMO of 0.86. Several sensitivity studies are performed to ascertain the degree of complexity needed to match observations; including the oxalic acid enhancement is necessary, while different parameterizations for calculating model oxalate concentrations are less important. The percent change in soluble iron deposition between the reference case (REF) and the simulation with acidic processing alone is 63.8%, which is consistent with previous studies. Upon deposition to global oceans, global mean combustion iron solubility to total fractional iron solubility is 8.2%; however, the contribution of fractional iron solubility from combustion sources to ocean basins below 15°S is approximately 50%. We conclude that, in many remote ocean regions, sources of iron from combustion and dust aerosols are equally important. Our estimates of changes in deposition of soluble iron to the ocean since preindustrial climate conditions suggest roughly a doubling due to a combination of higher dust and combustion iron emissions along with more efficient atmospheric processing
Recommended from our members
Aerosol trace metal leaching and impacts on marine microorganisms
Metal dissolution from atmospheric aerosol deposition to the oceans is important in enhancing and inhibiting phytoplankton growth rates and modifying plankton community structure, thus impacting marine biogeochemistry. Here we review the current state of knowledge on the causes and effects of the leaching of multiple trace metals from natural and anthropogenic aerosols. Aerosol deposition is considered both on short timescales over which phytoplankton respond directly to aerosol metal inputs, as well as longer timescales over which biogeochemical cycles are affected by aerosols
Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study
This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and atmospheric concentrations and the analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry transport (CTMs) and general circulation (GCMs) models participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, The Atmospheric Input of Chemicals to the Ocean. The global total Fe (TFe) emission strength in the models is equal to ââŒâ72TgâFeâyrâ1 (38â134TgâFeâyrâ1) from mineral dust sources and around 2.1TgâFeâyrâ1 (1.8â2.7TgâFeâyrâ1) from combustion processes (the sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3)TgâFeâyrâ1, accounting for both mineral dust and combustion aerosols. The mean global deposition fluxes into the global ocean are estimated to be in the range of 10â30 and 0.2â0.4TgâFeâyrâ1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3TgâFeâyrâ1 for the multi-model ensemble model mean. The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parameterizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicates that most models overestimate surface level TFe mass concentrations near dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe concentrations near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (ââŒâ14), larger than that of the Southern Hemisphere (ââŒâ2.4) for the ensemble model mean. This model intercomparison and modelâobservation comparison study reveals two critical issues in LFe simulations that require further exploration: (1) the Fe-containing aerosol size distribution and (2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions
Pyrogenic iron: The missing link to high iron solubility in aerosols
Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity
Modeling dust as component minerals in the Community Atmosphere Model: development of framework and impact on radiative forcing
The mineralogy of desert dust is important due to its effect on radiation,
clouds and biogeochemical cycling of trace nutrients. This study presents
the simulation of dust radiative forcing as a function of both mineral
composition and size at the global scale, using mineral soil maps for
estimating emissions. Externally mixed mineral aerosols in the bulk aerosol
module in the Community Atmosphere Model version 4 (CAM4) and internally
mixed mineral aerosols in the modal aerosol module in the Community
Atmosphere Model version 5.1 (CAM5) embedded in the Community Earth System
Model version 1.0.5 (CESM) are speciated into common mineral components in
place of total dust. The simulations with mineralogy are compared to
available observations of mineral atmospheric distribution and deposition
along with observations of clear-sky radiative forcing efficiency. Based on
these simulations, we estimate the all-sky direct radiative forcing at the
top of the atmosphere as + 0.05 Wm<sup>â2</sup> for both CAM4 and CAM5
simulations with mineralogy. We compare this to the radiative forcing from
simulations of dust in release versions of CAM4 and CAM5 (+0.08 and
+0.17 Wm<sup>â2</sup>) and of dust with optimized optical properties, wet
scavenging and particle size distribution in CAM4 and CAM5, â0.05
and â0.17 Wm<sup>â2</sup>, respectively. The ability to correctly include the mineralogy of
dust in climate models is hindered by its spatial and temporal variability
as well as insufficient global in situ observations, incomplete and
uncertain source mineralogies and the uncertainties associated with data
retrieved from remote sensing methods
Recommended from our members
Pyrogenic iron: The missing link to high iron solubility in aerosols.
Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity
Recommended from our members
Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study
Abstract. This work reports on the current status of the global modeling of iron (Fe)
deposition fluxes and atmospheric concentrations and the analyses of the
differences between models, as well as between models and observations. A
total of four global 3-D chemistry transport (CTMs) and general circulation
(GCMs) models participated in this intercomparison, in the framework of
the United Nations Joint Group of Experts on the Scientific Aspects of Marine
Environmental Protection (GESAMP) Working Group 38, âThe Atmospheric Input
of Chemicals to the Oceanâ. The global total Fe (TFe) emission strength in
the models is equal to âŒ72âTgâFeâyrâ1 (38â134âTgâFeâyrâ1)
from mineral dust sources and around 2.1âTgâFeâyrâ1 (1.8â2.7âTgâFeâyrâ1)
from combustion processes (the sum of anthropogenic
combustion/biomass burning and wildfires). The mean global labile Fe (LFe)
source strength in the models, considering both the primary emissions and the
atmospheric processing, is calculated to be 0.7 (±0.3)âTgâFeâyrâ1,
accounting for both mineral dust and combustion aerosols. The
mean global deposition fluxes into the global ocean are estimated to be in the range
of 10â30 and 0.2â0.4âTgâFeâyrâ1 for TFe and LFe, respectively,
which roughly corresponds to a respective 15 and 0.3âTgâFeâyrâ1 for the multi-model ensemble model mean. The model intercomparison analysis indicates that the representation of the
atmospheric Fe cycle varies among models, in terms of both the magnitude of
natural and combustion Fe emissions as well as the complexity of atmospheric
processing parameterizations of Fe-containing aerosols. The model comparison
with aerosol Fe observations over oceanic regions indicates that most models
overestimate surface level TFe mass concentrations near dust source
regions and tend to underestimate the low concentrations observed in remote
ocean regions. All models are able to simulate the tendency of higher Fe
concentrations near and downwind from the dust source regions, with the mean
normalized bias for the Northern Hemisphere (âŒ14), larger
than that of the Southern Hemisphere (âŒ2.4) for the ensemble model
mean. This model intercomparison and modelâobservation comparison study
reveals two critical issues in LFe simulations that require further
exploration: (1) the Fe-containing aerosol size distribution and (2) the
relative contribution of dust and combustion sources of Fe to labile Fe in
atmospheric aerosols over the remote oceanic regions
Smaller desert dust cooling effect estimated from analysis of dust size and abundance
International audienc