scholarly journals Sensitivity of sulphate aerosol size distributions and CCN concentrations over North America to SOxemissions and H2O2concentrations

2000 ◽  
Vol 105 (D8) ◽  
pp. 9741-9765 ◽  
Author(s):  
K. von Salzen ◽  
H. G. Leighton ◽  
P. A. Ariya ◽  
L. A. Barrie ◽  
S. L. Gong ◽  
...  
Keyword(s):  
North America ◽  
Size Distributions ◽  
Sulphate Aerosol

Massive volcanic SO2 oxidation and sulphate aerosol deposition in Cenozoic North America

Nature ◽  
2010 ◽  
Vol 465 (7300) ◽  
pp. 909-912 ◽  
Author(s):  
Huiming Bao ◽  
Shaocai Yu ◽  
Daniel Q. Tong
Keyword(s):  
North America ◽  
Aerosol Deposition ◽  
Sulphate Aerosol ◽  
So2 Oxidation

scholarly journals Intra-guild competition and its implications for one of the biggest terrestrial predators, Tyrannosaurus rex

2011 ◽  
Vol 278 (1718) ◽  
pp. 2682-2690 ◽  
Author(s):  
Chris Carbone ◽  
Samuel T. Turvey ◽  
Jon Bielby
Keyword(s):  
North America ◽  
Late Cretaceous ◽  
Food Source ◽  
Feeding Strategy ◽  
Past Century ◽  
Size Distributions ◽  
Ecological Context ◽  
The Past ◽  
The Subject ◽  
Active Predator

Identifying tradeoffs between hunting and scavenging in an ecological context is important for understanding predatory guilds. In the past century, the feeding strategy of one of the largest and best-known terrestrial carnivores, Tyrannosaurus rex , has been the subject of much debate: was it an active predator or an obligate scavenger? Here we look at the feasibility of an adult T. rex being an obligate scavenger in the environmental conditions of Late Cretaceous North America, given the size distributions of sympatric herbivorous dinosaurs and likely competition with more abundant small-bodied theropods. We predict that nearly 50 per cent of herbivores would have been within a 55–85 kg range, and calculate based on expected encounter rates that carcasses from these individuals would have been quickly consumed by smaller theropods. Larger carcasses would have been very rare and heavily competed for, making them an unreliable food source. The potential carcass search rates of smaller theropods are predicted to be 14–60 times that of an adult T. rex . Our results suggest that T. rex and other extremely large carnivorous dinosaurs would have been unable to compete as obligate scavengers and would have primarily hunted large vertebrate prey, similar to many large mammalian carnivores in modern-day ecosystems.

scholarly journals Source identification and airborne chemical characterisation of aerosol pollution from long-range transport over Greenland during POLARCAT summer campaign 2008

2011 ◽  
Vol 11 (3) ◽  
pp. 7593-7658 ◽  
Author(s):  
J. Schmale ◽  
J. Schneider ◽  
G. Ancellet ◽  
B. Quennehen ◽  
A. Stohl ◽  
...  
Keyword(s):  
Chemical Composition ◽  
North America ◽  
North American ◽  
Dispersion Model ◽  
Mean Value ◽  
Particle Dispersion ◽  
Gas Analysis ◽  
Size Distributions ◽  
Transport Pathways ◽  
June July

Abstract. We deployed an aerosol mass spectrometer during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) summer campaign in Greenland in June/July 2008 on the research aircraft ATR-42. Online size resolved chemical composition data of submicron aerosol were collected up to 7.6 km altitude in the region 60 to 71° N and 40 to 60° W. Biomass burning (BB) and fossil fuel combustion (FF) plumes originating from North America, Asia, Siberia and Europe were sampled. Transport pathways of detected plumes included advection below 700 hPa, air mass uplifting in warm conveyor belts, and high altitude transport in the upper troposphere. By means of the Lagrangian particle dispersion model FLEXPART, trace gas analysis of O3 and CO, particle size distributions and aerosol chemical composition 48 pollution events were identified and classified into five chemically distinct categories. Aerosol from North American BB consisted of 22% particulate sulphate, while with increasing anthropogenic and Asian influence aerosol was composed of up to 37% sulphate category mean value. Overall, it was found that the organic matter fraction was larger (85%) in pollution plumes than for background conditions (71%). Despite different source regions and emission types the particle oxygen to carbon ratio of all plume classes was around 1 indicating low-volatile highly oxygenated aerosol. Also the volume size distributions were rather similar for all sampled plume categories. This can be explained by the relatively long transport times of roughly one week from North America and two weeks from Asia/Siberia. The derived aerosol lifetime for North American emissions was about 9 ± 2 days.

scholarly journals Interpretation of Measured Aerosol Mass Scattering Efficiency Over North America Using a Chemical Transport Model

2018 ◽  
Author(s):  
Robyn N. C. Latimer ◽  
Randall V. Martin
Keyword(s):  
North America ◽  
Transport Model ◽  
Chemical Transport ◽  
Satellite Observations ◽  
Climate Forcing ◽  
Size Distributions ◽  
Positive Bias ◽  
Chemical Transport Model ◽  
Scattering Efficiency ◽  
Aerosol Mass

Abstract. Aerosol mass scattering efficiency affects climate forcing calculations, atmospheric visibility, and the interpretation of satellite observations of aerosol optical depth. We evaluated the representation of aerosol mass scattering efficiency (αsp) in the GEOS-Chem chemical transport model over North America using collocated measurements of aerosol scatter and mass from IMPROVE network sites between 2000–2015. We found a positive bias in mass scattering efficiency given current assumptions of aerosol size distributions and particle hygroscopicity in the model. We found that overestimation of mass scattering efficiency was most significant in dry (RH 

scholarly journals Evaluation of the Community Multiscale Air Quality (CMAQ) model v5.0 against size-resolved measurements of inorganic particle composition across sites in North America

2015 ◽  
Vol 8 (5) ◽  
pp. 3861-3904 ◽  
Author(s):  
C. G. Nolte ◽  
K. W. Appel ◽  
J. T. Kelly ◽  
P. V. Bhave ◽  
K. M. Fahey ◽  
...  
Keyword(s):  
Air Quality ◽  
North America ◽  
National Parks ◽  
Particle Concentration ◽  
Particle Diameter ◽  
Model Performance ◽  
The United States ◽  
Sea Spray ◽  
Size Distributions ◽  
Aerosol Model

Abstract. This work evaluates particle size-composition distributions simulated by the Community Multiscale Air Quality (CMAQ) model using Micro-Orifice Uniform Deposit Impactor (MOUDI) measurements at 18 sites across North America. Size-resolved measurements of particulate SO42−, NO3−, NH4+, Na+, Cl−, Mg2+, Ca2+ and K+ are compared to CMAQ model output for discrete sampling periods between 2002 and 2005. The observation sites were predominantly in remote areas (e.g. National Parks) in the United States and Canada, and measurements were typically made for a period of roughly one month. For SO42− and NH4+, model performance was consistent across the US and Canadian sites, with the model slightly overestimating the peak particle diameter and underestimating the peak particle concentration compared to the observations. Na+ and Mg2+ size distributions were generally well represented at coastal sites, indicating reasonable simulation of emissions from sea spray. CMAQ is able to simulate the displacement of Cl− in aged sea spray aerosol, though the extent of Cl− depletion relative to Na+ is often underpredicted. The model performance for NO3− exhibited much more site-to-site variability than that of SO42− and NH4+, with the model ranging from an underestimation to overestimation of both the peak diameter and peak particle concentration across the sites. Computing PM2.5 from the modeled size distribution parameters rather than by summing the masses in the Aitken and accumulation modes resulted in differences in daily averages of up to 1 μg m−3 (10%), while the difference in seasonal and annual model performance compared to observations from the IMPROVE, CSN and AQS networks was very small. Two updates to the CMAQ aerosol model – changes to the assumed size and mode width of emitted particles and the implementation of gravitational settling – resulted in small improvements in modeled size distributions.

scholarly journals Evaluation of the Community Multiscale Air Quality (CMAQ) model v5.0 against size-resolved measurements of inorganic particle composition across sites in North America

2015 ◽  
Vol 8 (9) ◽  
pp. 2877-2892 ◽  
Author(s):  
C. G. Nolte ◽  
K. W. Appel ◽  
J. T. Kelly ◽  
P. V. Bhave ◽  
K. M. Fahey ◽  
...  
Keyword(s):  
Air Quality ◽  
North America ◽  
National Parks ◽  
Particle Concentration ◽  
Particle Diameter ◽  
Model Performance ◽  
Sea Spray ◽  
Size Distributions ◽  
Aerosol Model ◽  
The Usa

Abstract. This work evaluates particle size–composition distributions simulated by the Community Multiscale Air Quality (CMAQ) model using micro-orifice uniform deposit impactor (MOUDI) measurements at 18 sites across North America. Size-resolved measurements of particulate SO42−, NO3−, NH4+, Na+, Cl−, Mg2+, Ca2+, and K+ are compared to CMAQ model output for discrete sampling periods between 2002 and 2005. The observation sites were predominantly in remote areas (e.g., National Parks) in the USA and Canada, and measurements were typically made for a period of roughly 1 month. For SO42− and NH4+, model performance was consistent across the USA and Canadian sites, with the model slightly overestimating the peak particle diameter and underestimating the peak particle concentration compared to the observations. Na+ and Mg2+ size distributions were generally well represented at coastal sites, indicating reasonable simulation of emissions from sea spray. CMAQ is able to simulate the displacement of Cl− in aged sea spray aerosol, though the extent of Cl− depletion relative to Na+ is often underpredicted. The model performance for NO3− exhibited much more site-to-site variability than that of SO42− and NH4+, with the model ranging from an underestimation to overestimation of both the peak diameter and peak particle concentration across the sites. Computing PM2.5 from the modeled size distribution parameters rather than by summing the masses in the Aitken and accumulation modes resulted in differences in daily averages of up to 1 μg m−3 (10 %), while the difference in seasonal and annual model performance compared to observations from the Interagency Monitoring of Protected Visual Environments (IMPROVE), Chemical Speciation Network (CSN), and Air Quality System (AQS) networks was very small. Two updates to the CMAQ aerosol model – changes to the assumed size and mode width of emitted particles and the implementation of gravitational settling – resulted in small improvements in modeled size distributions.

scholarly journals Physical and chemical properties of pollution aerosol particles transported from North America to Greenland as measured during the POLARCAT summer campaign

2011 ◽  
Vol 11 (21) ◽  
pp. 10947-10963 ◽  
Author(s):  
B. Quennehen ◽  
A. Schwarzenboeck ◽  
J. Schmale ◽  
J. Schneider ◽  
H. Sodemann ◽  
...  
Keyword(s):  
North America ◽  
Black Carbon ◽  
Refractory Material ◽  
Aerosol Particles ◽  
Size Distributions ◽  
American Continent ◽  
Air Masses ◽  
Accumulation Mode ◽  
North American Continent ◽  
The North

Abstract. Within the framework of the POLARCAT-France campaign, aerosol physical, chemical and optical properties over Greenland were measured onboard the French ATR-42 research aircraft. The origins of CO excess peaks detected in the aircraft measurements then have been identified through FLEXPART simulations. The study presented here focuses particularly on the characterization of air masses transported from the North American continent to Greenland. Air masses that picked up emissions from Canadian boreal forest fires as well as from the cities on the American east coast were identified and selected for a detailed study. Measurements of CO concentrations, aerosol chemical composition, aerosol number size distributions, aerosol volume volatile fractions and aerosol light absorption (mainly from black carbon) are used in order to study the relationship between CO enhancement (ΔCO), aerosol particle concentrations and number size distributions. Aerosol number size distributions (normalised with their respective ΔCO) are in good agreement with previous studies. Nonetheless, wet scavenging may have occurred along the pathway between the emission sources and Greenland leading to a less pronounced accumulation mode in the POLARCAT data. Chemical analyses from mass spectrometry show that submicrometer aerosol particles are mainly composed of sulphate and organics. The observed bimodal (Aitken and accumulation) aerosol number size distributions show a significant enhancement in Aitken mode particles. Furthermore, results from the thermodenuder analysis demonstrate the external mixture of boreal fire (BF) air masses from North America (NA). This is particularly observed in the accumulation mode, containing a volume fraction of up to 25–30% of refractory material at the applied temperature of 280 °C. NA anthropogenic air masses with only 6% refractory material in the accumulation mode can be clearly distinguished from BF air masses. Overall, during the campaign rather small amounts of black carbon from the North American continent were transported towards Greenland during the summer POLARCAT observation period, which also is a valuable finding with respect to potential climate impacts of black carbon in the Arctic.

Sulphate aerosol size distributions at Mumbai, India, during the INDOEX-FFP (1998)

2001 ◽  
Vol 35 (15) ◽  
pp. 2647-2655 ◽  
Author(s):  
Chandra Venkataraman ◽  
Prashant Sinha ◽  
Sachin Bammi
Keyword(s):  
Size Distributions ◽  
Sulphate Aerosol

scholarly journals Validation of demographic equilibrium theory against tree-size distributions and biomass density in Amazonia

2020 ◽  
Vol 17 (4) ◽  
pp. 1013-1032 ◽  
Author(s):  
Jonathan R. Moore ◽  
Arthur P. K. Argles ◽  
Kai Zhu ◽  
Chris Huntingford ◽  
Peter M. Cox
Keyword(s):  
North America ◽  
Tree Mortality ◽  
Equilibrium Theory ◽  
Tree Size ◽  
Necessary Condition ◽  
Size Distributions ◽  
Metabolic Scaling ◽  
Trunk Diameter ◽  
Trade Offs ◽  
Best Fit

Abstract. Predicting the response of forests to climate and land-use change depends on models that can simulate the time-varying distribution of different tree sizes within a forest – so-called forest demography models. A necessary condition for such models to be trustworthy is that they can reproduce the tree-size distributions that are observed within existing forests worldwide. In a previous study, we showed that demographic equilibrium theory (DET) is able to fit tree-diameter distributions for forests across North America, using a single site-specific fitting parameter (μ) which represents the ratio of the rate of mortality to growth for a tree of a reference size. We use a form of DET that assumes tree-size profiles are in a steady state resulting from the balance between a size-independent rate of tree mortality and tree growth rates that vary as a power law of tree size (as measured by either trunk diameter or biomass). In this study, we test DET against ForestPlots data for 124 sites across Amazonia, fitting, using maximum likelihood estimation, to both directly measured trunk diameter data and also biomass estimates derived from published allometric relationships. Again, we find that DET fits the observed tree-size distributions well, with best-fit values of the exponent relating growth rate to tree mass giving a mean of ϕ=0.71 (0.31 for trunk diameter). This finding is broadly consistent with exponents of ϕ=0.75 (ϕ=1/3 for trunk diameter) predicted by metabolic scaling theory (MST) allometry. The fitted ϕ and μ parameters also show a clear relationship that is suggestive of life-history trade-offs. When we fix to the MST value of ϕ=0.75, we find that best-fit values of μ cluster around 0.25 for trunk diameter, which is similar to the best-fit value we found for North America of 0.22. This suggests an as yet unexplained preferred ratio of mortality to growth across forests of very different types and locations.

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