scholarly journals Sources of uncertainties in modelling black carbon at the global scale

2010 ◽  
Vol 10 (6) ◽  
pp. 2595-2611 ◽  
Author(s):  
E. Vignati ◽  
M. Karl ◽  
M. Krol ◽  
J. Wilson ◽  
P. Stier ◽  
...  
Keyword(s):  
Black Carbon ◽  
Large Scale ◽  
Elemental Carbon ◽  
Removal Rate ◽  
Global Scale ◽  
Polar Regions ◽  
Emission Inventories ◽  
Simplified Approach ◽  
Microphysical Properties ◽  
Carbon Concentrations

Abstract. Our understanding of the global black carbon (BC) cycle is essentially qualitative due to uncertainties in our knowledge of its properties. This work investigates two source of uncertainties in modelling black carbon: those due to the use of different schemes for BC ageing and its removal rate in the global Transport-Chemistry model TM5 and those due to the uncertainties in the definition and quantification of the observations, which propagate through to both the emission inventories, and the measurements used for the model evaluation. The schemes for the atmospheric processing of black carbon that have been tested with the model are (i) a simple approach considering BC as bulk aerosol and a simple treatment of the removal with fixed 70% of in-cloud black carbon concentrations scavenged by clouds and removed when rain is present and (ii) a more complete description of microphysical ageing within an aerosol dynamics model, where removal is coupled to the microphysical properties of the aerosol, which results in a global average of 40% in-cloud black carbon that is scavenged in clouds and subsequently removed by rain, thus resulting in a longer atmospheric lifetime. This difference is reflected in comparisons between both sets of modelled results and the measurements. Close to the sources, both anthropogenic and vegetation fire source regions, the model results do not differ significantly, indicating that the emissions are the prevailing mechanism determining the concentrations and the choice of the aerosol scheme does not influence the levels. In more remote areas such as oceanic and polar regions the differences can be orders of magnitude, due to the differences between the two schemes. The more complete description reproduces the seasonal trend of the black carbon observations in those areas, although not always the magnitude of the signal, while the more simplified approach underestimates black carbon concentrations by orders of magnitude. The sensitivity to wet scavenging has been tested by varying in-cloud and below-cloud removal. BC lifetime increases by 10% when large scale and convective scale precipitation removal efficiency are reduced by 30%, while the variation is very small when below-cloud scavenging is zero. Since the emission inventories are representative of elemental carbon-like substance, the model output should be compared to elemental carbon measurements and if known, the ratio of black carbon to elemental carbon mass should be taken into account when the model is compared with black carbon observations.

scholarly journals Sources of uncertainties in modelling Black Carbon at the global scale

2009 ◽  
Vol 9 (6) ◽  
pp. 24317-24360 ◽  
Author(s):  
E. Vignati ◽  
M. Karl ◽  
M. Krol ◽  
J. Wilson ◽  
P. Stier ◽  
...  
Keyword(s):  
Black Carbon ◽  
Large Scale ◽  
Elemental Carbon ◽  
Removal Rate ◽  
Global Scale ◽  
Polar Regions ◽  
Emission Inventories ◽  
Simplified Approach ◽  
Aerosol Dynamics ◽  
Microphysical Properties

Abstract. Our understanding of the global black carbon cycle is essentially qualitative due to uncertainties in our knowledge of the properties of black carbon. This work investigates uncertainties related to modelling black carbon: due to the use of different schemes for BC ageing and its removal rate in the global Transport-Chemistry model TM5 and due to the uncertainties in the definition and quantification of observed black carbon, which propagate through to both the emission inventories, and the measurements used for the model evaluation. The schemes for the atmospheric processing of black carbon that have been tested with the model are (i) a simple approach considering black carbon as bulk aerosol and a simple treatment in the removal and (ii) a more complete description of microphysical aging within an aerosol dynamics model, where removal is coupled to the microphysical properties of the aerosol. In the first approach a fixed 70% of black carbon is scavenged in clouds and removed when rain is present. The second leads to a global average of 40% black carbon that is scavenged in clouds and subsequently removed by rain, thus resulting in a longer lifetime. This difference is reflected in comparisons between both sets of modelled results and the measurements. Close to the sources, both anthropogenic and vegetation fire source regions, the model results do not differ significantly, showing that the emissions are the prevailing mechanism determining the concentrations and the choice of the aerosol scheme does not influence the levels. In more remote areas such as oceanic and polar regions the differences can be orders of magnitude, due to the differences between the two schemes. The more complete description reproduces the seasonal trend of the black carbon observations in those areas, although not always the magnitude of the signal, while the more simplified approach underestimates black carbon concentrations by orders of magnitude. The sensitivity to wet scavenging has been tested varying in-cloud and below-cloud removals. BC lifetime increases by 10% when large scale and convective scale precipitation are reduced by 30%, while the variation is very small when below-cloud scavenging is zero. Since the emission inventories are representative of elemental carbon-like substance, the model output should be compared to elemental carbon measurements, and, if known, the ratio of black carbon to elemental carbon mass should be taken into account when the model is compared with black carbon observations.

scholarly journals Decadal trends in global CO emissions as seen by MOPITT

2015 ◽  
Vol 15 (23) ◽  
pp. 13433-13451 ◽  
Author(s):  
Y. Yin ◽  
F. Chevallier ◽  
P. Ciais ◽  
G. Broquet ◽  
A. Fortems-Cheiney ◽  
...  
Keyword(s):  
Large Scale ◽  
Western Europe ◽  
Model Simulation ◽  
Recent Decade ◽  
The United States ◽  
Global Scale ◽  
Emission Inventories ◽  
Co Concentration ◽  
Co Concentrations ◽  
Atmospheric Inversion

Abstract. Negative trends of carbon monoxide (CO) concentrations are observed in the recent decade by both surface measurements and satellite retrievals over many regions of the globe, but they are not well explained by current emission inventories. Here, we analyse the observed CO concentration decline with an atmospheric inversion that simultaneously optimizes the two main CO sources (surface emissions and atmospheric hydrocarbon oxidations) and the main CO sink (atmospheric hydroxyl radical OH oxidation). Satellite CO column retrievals from Measurements of Pollution in the Troposphere (MOPITT), version 6, and surface observations of methane and methyl chloroform mole fractions are assimilated jointly for the period covering 2002–2011. Compared to the model simulation prescribed with prior emission inventories, trends in the optimized CO concentrations show better agreement with that of independent surface in situ measurements. At the global scale, the atmospheric inversion primarily interprets the CO concentration decline as a decrease in the CO emissions (−2.3 % yr−1), more than twice the negative trend estimated by the prior emission inventories (−1.0 % yr−1). The spatial distribution of the inferred decrease in CO emissions indicates contributions from western Europe (−4.0 % yr−1), the United States (−4.6 % yr−1) and East Asia (−1.2 % yr−1), where anthropogenic fuel combustion generally dominates the overall CO emissions, and also from Australia (−5.3 % yr−1), the Indo-China Peninsula (−5.6 % yr−1), Indonesia (−6.7 % y−1), and South America (−3 % yr−1), where CO emissions are mostly due to biomass burning. In contradiction with the bottom-up inventories that report an increase of 2 % yr−1 over China during the study period, a significant emission decrease of 1.1 % yr−1 is inferred by the inversion. A large decrease in CO emission factors due to technology improvements would outweigh the increase in carbon fuel combustions and may explain this decrease. Independent satellite formaldehyde (CH2O) column retrievals confirm the absence of large-scale trends in the atmospheric source of CO. However, it should be noted that the CH2O retrievals are not assimilated and OH concentrations are optimized at a very large scale in this study.

scholarly journals The T1-T2 study: evolution of aerosol properties downwind of Mexico City

2007 ◽  
Vol 7 (6) ◽  
pp. 1585-1598 ◽  
Author(s):  
J. C. Doran ◽  
J. C. Barnard ◽  
W. P. Arnott ◽  
R. Cary ◽  
R. Coulter ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Mexico City ◽  
Atmospheric Chemistry ◽  
Elemental Carbon ◽  
Early Morning ◽  
Specific Absorption ◽  
The North ◽  
T1 And T2 ◽  
Carbon Concentrations

Abstract. As part of a major atmospheric chemistry and aerosol field program carried out in March 2006, a study was conducted in the area to the north and northeast of Mexico City to investigate the evolution of aerosols and their associated optical properties in the first few hours after their emission. The focus of the T1-T2 aerosol study was to investigate changes in the specific absorption αABS (absorption per unit mass, with unit of m2 g−1) of black carbon as it aged and became coated with compounds such as sulfate and organic carbon, evolving from an external to an internal mixture. Such evolution has been reported in previous studies. The T1 site was located just to the north of the Mexico City metropolitan area; the T2 site was situated approximately 35 km farther to the northeast. Nephelometers, particle soot absorption photometers, photoacoustic absorption spectrometers, and organic and elemental carbon analyzers were used to measure the optical properties of the aerosols and the carbon concentrations at each of the sites. Radar wind profilers and radiosonde systems helped to characterize the meteorology and to identify periods when transport from Mexico City over T1 and T2 occurred. Organic and elemental carbon concentrations at T1 showed diurnal cycles reflecting the nocturnal and early morning buildup from nearby sources, while concentrations at T2 appeared to be more affected by transport from Mexico City. Specific absorption during transport periods was lower than during other times, consistent with the likelihood of fresher emissions being found when the winds blew from Mexico City over T1 and T2. The specific absorption at T2 was larger than at T1, which is also consistent with the expectation of more aged particles with encapsulated black carbon being found at the more distant location. In situ measurements of single scattering albedo with an aircraft and a ground station showed general agreement with column-averaged values derived from rotating shadowband radiometer data, although some differences were found that may be related to boundary-layer evolution.

scholarly journals Large-Scale Analysis of Cirrus Clouds from AVHRR Data: Assessment of Both a Microphysical Index and the Cloud-Top Temperature

1997 ◽  
Vol 36 (6) ◽  
pp. 664-675 ◽  
Author(s):  
V. Giraud ◽  
J. C. Buriez ◽  
Y. Fouquart ◽  
F. Parol ◽  
G. Seze
Keyword(s):  
Absorption Coefficient ◽  
Size Distribution ◽  
Large Scale ◽  
Global Scale ◽  
Cirrus Clouds ◽  
Automatic Analysis ◽  
Effective Diameter ◽  
Microphysical Properties ◽  
Cloud Temperature ◽  
Cloud Top Temperature

Abstract An algorithm that allows an automatic analysis of cirrus properties from Advanced Very High Resolution Radiometer (AVHRR) observations is presented. Further investigations of the information content and physical meaning of the brightness temperature differences (BTD) between channels 4 (11 μm) and 5 (12 μm) of the radiometer have led to the development of an automatic procedure to provide global estimates both of the cirrus cloud temperature and of the ratio of the equivalent absorption coefficients in the two channels, accounting for scattering effects. The ratio is useful since its variations are related to differences in microphysical properties. Assuming that cirrus clouds are composed of ice spheres, the effective diameter of the particle size distribution can be deduced from this microphysical index. The automatic procedure includes first, a cloud classification and a selection of the pixels corresponding to the envelope of the BTD diagram observed at a scale of typically 100 × 100 pixels. The classification, which uses dynamic cluster analysis, takes into account spectral and spatial properties of the AVHRR pixels. The selection is made through a series of tests, which also guarantees that the BTD diagram contains the necessary information, such as the presence of both cirrus-free pixels and pixels totally covered by opaque cirrus in the same area. Finally, the cloud temperature and the equivalent absorption coefficient ratio are found by fitting the envelope of the BTD diagram with a theoretical curve. Note that the method leads to the retrieval of the maximum value of the equivalent absorption coefficient ratio in the scene under consideration. This, in turn, corresponds to the minimum value of the effective diameter of the size distribution of equivalent Mie particles. The automatic analysis has been applied to a series of 21 AVHRR images acquired during the International Cirrus Experiment (ICE’89). Although the dataset is obviously much too limited to draw any conclusion at the global scale, it is large enough to permit derivation of cirrus properties that are statistically representative of the cirrus systems contained therein. The authors found that on average, the maximum equivalent absorption coefficient ratio increases with the cloud-top temperature with a jump between 235 and 240 K. More precisely, for cloud temperatures warmer than 235 K, the retrieved equivalent absorption coefficient ratio sometimes corresponds to very small equivalent spheres (diameter smaller than 20 μm). This is never observed for lower cloud temperatures. This change in cirrus microphysical properties points out that ice crystal habits may vary from one temperature regime toanother. It may be attributed to a modification of the size and/or shape of the particles.

scholarly journals Aerosol forcing based on CAM5 and AM3 meteorological fields

2012 ◽  
Vol 12 (20) ◽  
pp. 9629-9652 ◽  
Author(s):  
C. Zhou ◽  
J. E. Penner ◽  
Y. Ming ◽  
X. L. Huang
Keyword(s):  
Black Carbon ◽  
Wet Deposition ◽  
Large Scale ◽  
Liquid Water Content ◽  
Polar Regions ◽  
Hygroscopic Growth ◽  
Annual Average ◽  
Aerosol Model ◽  
Aerosol Forcing ◽  
The Impact

Abstract. We use a single aerosol model to explore the effects of the differing meteorological fields from the NCAR CAM5 and GFDL AM3 models. We simulate the global distributions of sulfate, black carbon, organic matter, dust and sea salt using the University of Michigan IMPACT model and use these fields to calculate aerosol direct and indirect forcing, thereby isolating the impacts of the differing meteorological fields. Over all, the IMPACT-AM3 model predicts larger burdens and longer aerosol lifetimes than the IMPACT-CAM5 model. However, the IMPACT-CAM5 simulations transport more black carbon to the polar regions and more dust from Asia towards North America. These differences can mainly be attributed to differences in: (1) the vertical cloud mass flux and large-scale precipitation fields which determine the wet deposition of aerosols; (2) the in-cloud liquid water content and the cloud coverage which determine the wet aqueous phase production of sulfate. The burden, lifetime and global distribution, especially black carbon in polar regions, are strongly affected by choice of the parameters used for wet deposition. The total annual mean aerosol optical depth (AOD) at 550 nm ranges from 0.087 to 0.122 for the IMPACT-AM3 model and from 0.138 to 0.186 for the IMPACT-CAM5 model (range is due to different parameters used for wet deposition). Even though IMPACT-CAM5 has smaller aerosol burdens, its AOD is larger due to the much higher relative humidity in CAM5 which leads to more hygroscopic growth. The corresponding global annual average anthropogenic and all-sky aerosol direct forcing at the top of the atmosphere ranges from −0.25 W m−2 to −0.30 W m−2 for IMPACT-AM3 and from −0.48 W m−2 to −0.64 W m−2 for IMPACT-CAM5. The global annual average anthropogenic 1st aerosol indirect effect at the top of the atmosphere ranges from −1.26 W m−2 to −1.44 W m−2 for IMPACT-AM3 and from −1.74 W m−2 to −1.77 W m−2 for IMPACT-CAM5.

scholarly journals Aerosol forcing based on CAM5 and AM3 meteorological fields

2012 ◽  
Vol 12 (4) ◽  
pp. 10679-10727
Author(s):  
C. Zhou ◽  
J. E. Penner ◽  
Y. Ming ◽  
X. L. Huang
Keyword(s):  
Black Carbon ◽  
Wet Deposition ◽  
Large Scale ◽  
Liquid Water Content ◽  
Polar Regions ◽  
Hygroscopic Growth ◽  
Annual Average ◽  
Aerosol Model ◽  
Aerosol Forcing ◽  
The Impact

Abstract. We use a single aerosol model to explore the effects of the differing meteorological fields from the NCAR CAM5 and GFDL AM3 models. We simulate the global distributions of sulfate, black carbon, organic matter, dust and sea salt using the University of Michigan IMPACT model and use these fields to calculate aerosol direct and indirect forcing, thereby isolating the impacts of the differing meteorological fields. Over all, the IMPACT-AM3 model predicts larger burdens and longer aerosol lifetimes than the IMPACT-CAM5 model. However, the IMPACT-CAM5 simulations transport more black carbon to the polar regions and more dust from Asia towards North America. These differences can mainly be attributed to differences in: (1) the vertical cloud mass flux and large-scale precipitation fields which determine the wet deposition of aerosols; (2) the in-cloud liquid water content and the cloud coverage which determine the wet aqueous phase production of sulfate. The burden, lifetime and global distribution, especially black carbon in polar regions, are strongly affected by choice of the parameters used for wet deposition. The total annual mean aerosol optical depth (AOD) at 550 nm ranges from 0.087 to 0.122 for the IMPACT-AM3 model and from 0.138 to 0.186 for the IMPACT-CAM5 model (range is due to different parameters used for wet deposition). Even though IMPACT-CAM5 has smaller aerosol burdens, its AOD is larger due to the much higher relative humidity in CAM5 which leads to more hygroscopic growth. The corresponding global annual average anthropogenic and all-sky aerosol direct forcing at the top of the atmosphere ranges from −0.25 to −0.30 W m−2 for IMPACT-AM3 and from −0.48 to −0.64 W m−2 for IMPACT-CAM5. The global annual average anthropogenic 1st aerosol indirect effect at the top of the atmosphere ranges from −1.26 to −1.44 W m−2 for IMPACT-AM3 and from −1.74 to −1.77 W m−2 for IMPACT-CAM5.

scholarly journals Effects of Thermodynamics, Dynamics and Aerosols on Cirrus Clouds Based on In Situ Observations and NCAR CAM6 Model

2020 ◽  
Author(s):  
Ryan Patnaude ◽  
Minghui Diao ◽  
Xiaohong Liu ◽  
Suqian Chu
Keyword(s):  
Particle Growth ◽  
Global Scale ◽  
Controlling Factors ◽  
Cirrus Cloud ◽  
Polar Regions ◽  
Clear Sky ◽  
Microphysical Properties ◽  
Community Atmosphere Model ◽  
Ice Water Content ◽  
Ice Water

Abstract. Cirrus cloud radiative effects are largely affected by ice microphysical properties, including ice water content (IWC), ice crystal number concentration (Ni) and mean diameter (Di). These characteristics vary significantly due to thermodynamic, dynamical and aerosol conditions. In this work, a global-scale observation dataset is used to examine regional variations of cirrus cloud microphysical properties, as well as several key controlling factors, i.e., temperature, relative humidity with respect to ice (RHi), vertical velocity (w), and aerosol number concentrations (Na). Results are compared with simulations from the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 6 (CAM6). The differences between simulations and observations are found to vary with latitude and temperature. Specifically, simulations are found to underestimate IWC by a factor of 5–30 in all regions. Simulated Ni is overestimated in most regions except Northern Hemisphere midlatitude and polar regions. Simulated Di is underestimated, especially for warmer conditions (−50 °C to −40 °C) and higher Na, possibly due to less effective ice particle growth/sedimentation and weaker aerosol indirect effects, respectively. For RHi effects, the frequency and magnitude of ice supersaturation is underestimated in simulations for clear-sky conditions, and the simulated IWC and Ni show maximum values at 80 % RHi instead of 110 % as observed. For w effects, both observations and simulations show variances of w (σw) decreasing from tropics to polar regions, but simulations show much higher σw for in-cloud condition than clear-sky condition. These findings provide an observation-based guideline for improving simulated ice microphysical properties and their relationships with key controlling factors at various geographical locations.

scholarly journals Effects of thermodynamics, dynamics and aerosols on cirrus clouds based on in situ observations and NCAR CAM6

2021 ◽  
Vol 21 (3) ◽  
pp. 1835-1859
Author(s):  
Ryan Patnaude ◽  
Minghui Diao ◽  
Xiaohong Liu ◽  
Suqian Chu
Keyword(s):  
Particle Growth ◽  
Global Scale ◽  
Controlling Factors ◽  
Cirrus Cloud ◽  
Polar Regions ◽  
Clear Sky ◽  
Microphysical Properties ◽  
Community Atmosphere Model ◽  
Ice Water Content ◽  
Ice Water

Abstract. Cirrus cloud radiative effects are largely affected by ice microphysical properties, including ice water content (IWC), ice crystal number concentration (Ni) and mean diameter (Di). These characteristics vary significantly due to thermodynamic, dynamical and aerosol conditions. In this work, a global-scale observation dataset is used to examine regional variations of cirrus cloud microphysical properties, as well as several key controlling factors, i.e., temperature, relative humidity with respect to ice (RHi), vertical velocity (w) and aerosol number concentrations (Na). Results are compared with simulations from the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 6 (CAM6). Observed and simulated ice mass and number concentrations are constrained to ≥62.5 µm to reduce potential uncertainty from shattered ice in data collection. The differences between simulations and observations are found to vary with latitude and temperature. Comparing with averaged observations at ∼100 km horizontal scale, simulations are found to underestimate (overestimate) IWC by a factor of 3–10 in the Northern (Southern) Hemisphere. Simulated Ni is overestimated in most regions except the Northern Hemisphere midlatitudes. Simulated Di is underestimated by a factor of 2, especially for warmer conditions (−50 to −40 ∘C), possibly due to misrepresentation of ice particle growth/sedimentation. For RHi effects, the frequency and magnitude of ice supersaturation are underestimated in simulations for clear-sky conditions. The simulated IWC and Ni show bimodal distributions with maximum values at 100 % and 80 % RHi, differing from the unimodal distributions that peak at 100 % in the observations. For w effects, both observations and simulations show variances of w (σw) decreasing from the tropics to polar regions, but simulations show much higher σw for the in-cloud condition than the clear-sky condition. Compared with observations, simulations show weaker aerosol indirect effects with a smaller increase of IWC and Di at higher Na. These findings provide an observation-based guideline for improving simulated ice microphysical properties and their relationships with key controlling factors at various geographical locations.

scholarly journals The T1-T2 study: evolution of aerosol properties downwind of Mexico City

2006 ◽  
Vol 6 (6) ◽  
pp. 12967-12999
Author(s):  
J. C. Doran ◽  
W. P. Arnott ◽  
J. C. Barnard ◽  
R. Cary ◽  
R. Coulter ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Mexico City ◽  
Atmospheric Chemistry ◽  
Elemental Carbon ◽  
Early Morning ◽  
Specific Absorption ◽  
The North ◽  
T1 And T2 ◽  
Carbon Concentrations

Abstract. As part of a major atmospheric chemistry and aerosol field program carried out in March of 2006, a study was conducted in the area to the north and northeast of Mexico City to investigate the evolution of aerosols and their associated optical properties in the first few hours after their emission. The focus of the T1-T2 aerosol study was to investigate changes in the specific absorption αABS (absorption per unit mass, with unit of m2 g−1) of black carbon as it aged and became coated with compounds such as sulfate and organic carbon, evolving from an external to an internal mixture. Such evolution has been reported in previous studies. The T1 site was located just to the north of the Mexico City metropolitan area; the T2 site was situated approximately 35 km farther to the northeast. Nephelometers, particle soot absorption photometers, photoacoustic absorption photometers, and organic and elemental carbon analyzers were used to measure the optical properties of the aerosols and the carbon concentrations at each of the sites. Radar wind profilers and radiosonde systems helped to characterize the meteorology and to identify periods when transport from Mexico City over T1 and T2 occurred. Organic and elemental carbon concentrations at T1 showed diurnal cycles reflecting the nocturnal and early morning buildup from nearby sources, while concentrations at T2 appeared to be more affected by transport from Mexico City. Specific absorption during transport periods was lower than during other times, consistent with the likelihood of fresher emissions being found when the winds blew from Mexico City over T1 and T2. The specific absorption at T2 was larger than at T1, which is also consistent with the expectation of more aged particles with encapsulated black carbon being found at the more distant location. In situ measurements of single scattering albedo with an aircraft and a ground station showed general agreement with column-averaged values derived from rotating shadowband radiometer data, although some differences were found that may be related to boundary-layer evolution.

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