Sources,transport, and sinks of SO<Subscript>2</Subscript> over the equatorial Pacific during the Pacific Atmospheric Sulfur Experiment     

Burton Alonza Gray  Yuhang Wang  Dasa Gu  Alan Bandy  Lee Mauldin  Antony Clarke  Becky Alexander  Douglas D. Davis 《Journal of Atmospheric Chemistry》2011,68(1):27-53

The Pacific Atmospheric Sulfur Experiment (PASE) is the first sulfur-budget field experiment to feature simultaneous flux measurements of DMS marine emissions and SO₂ deposition to the ocean surface. We make use of these data to constrain a 1-D chemical transport model to study the production and loss pathways for DMS and SO₂ over the equatorial Pacific. Model results suggest that OH is the main sink for DMS in the boundary layer (BL), and the average DMS-to-SO₂ conversion efficiency is ~73%. In an exploratory run involving the addition of 1 pptv of BrO as a second oxidant, a 14% increase in the DMS flux is needed beyond that based on OH oxidation alone. This BrO addition also reduces the DMS-to-SO₂ conversion efficiency from 73% to 60%. The possibility of non-DMS sources of marine sulfur influencing the estimated conversion efficiency was explored and found to be unconvincing. For BL conditions, SO₂ losses consist of 48% dry deposition, while transport loss to the BuL and aerosol scavenging each account for another 19%. The conversion of SO₂ to H₂SO₄ consumes the final 14%. In the BuL, cloud scavenging removes 85% of the SO₂, thus resulting in a decreasing vertical profile for SO₂. The average SO₂ dry deposition velocity from direct measurements (i.e., 0.36 cm sec⁻¹) is approximately 50% of what is calculated from the 1-D model and the global GEOS-Chem model. This suggests that the current generation of global models may be significantly overestimating SO₂ deposition rates over some tropical marine areas. Although the specific mechanism cannot be determined, speculation here is that the dry deposition anomalous results may point to the presence of a micro-surface chemical phenomenon involving partial saturation with either S(IV) and/or S(VI) DMS oxidation products. This could also appear as a pH drop in the ocean’s surface microfilm layer in this region. Finally, we propose that the enhanced SO₂ level observed in the lower free troposphere versus that in the upper BuL during PASE is most likely the result of transported DMS/SO₂-rich free-tropospheric air parcels from the east of the PASE sampling area, rather than an inadequate representation in the model of local convection.  相似文献   

Pacific Atmospheric Sulfur Experiment (PASE): dynamics and chemistry of the south Pacific tropical trade wind regime     

Alan Bandy  Ian C. Faloona  Byron W. Blomquist  Barry J. Huebert  Antony D. Clarke  Steven G. Howell  R. L. Mauldin  Christopher A. Cantrell  James G. Hudson  Brian G. Heikes  John T. Merrill  Yuhang Wang  Daniel W. O��Sullivan  Wolfgang Nadler  Douglas D. Davis 《Journal of Atmospheric Chemistry》2011,68(1):5-25

The Pacific Atmospheric Sulfur Experiment (PASE) was a comprehensive airborne study of the chemistry and dynamics of the tropical trade wind regime (TWR) east of the island of Kiritibati (Christmas Island, 157º, 20?? W, 2º 52?? N). Christmas Island is located due south of Hawaii. Geographically it is in the northern hemisphere yet it is 6?C12º south of the intertropical convergence zone (ITCZ) which places it in the southern hemisphere meteorologically. Christmas Island trade winds in August and September are from east south east at 3?C15 ms^?1. Clouds, if present, are fair weather cumulus located in the middle layer of the TWR which is frequently labeled the buffer layer (BuL). PASE provided clear support for the idea that small particles (80 nm) were subsiding into the tropical trade wind regime (TWR) where sulfur chemistry transformed them to larger particles. Sulfur chemistry promoted the growth of some of these particles until they were large enough to activate to cloud drops. This process, promoted by sulfur chemistry, can produce a cooling effect due to the increase in cloud droplet density and changes in cloud droplet size. These increases in particle size observed in PASE promote additional cooling due to direct scattering from the aerosol. These potential impacts on the radiation balance in the TWR are enhanced by the high solar irradiance and ocean albedo of the TWR. Finally because of the large area involved there is a large factional impact on earth??s radiation budget. The TWR region near Christmas Island appears to be similar to the TWR that persists in August and September, from southwest of the Galapagos to at least Christmas Island. Transport in the TWR between the Galapagos and Christmas involves very little precipitation which could have removed the aerosol thus explaining at least in part the high concentrations of CCN (??300 at 0.5% supersaturation) observed in PASE. As expected the chemistry of sulfur in the trade winds was found to be initiated by the emission of DMS into the convective boundary layer (BL, the lowest of three layers). However, the efficiency with which this DMS is converted to SO₂ has been brought into further question by this study. This unusual result has come about as result of our using two totally different approaches for addressing this long standing question. In the first approach, based on accepted kinetic rate constants and detailed steps for the oxidation of DMS reflecting detailed laboratory studies, a DMS to SO₂ conversion efficiency of 60?C73% was determined. This range of values lies well within the uncertainties of previous studies. However, using a completely different approach, involving a budget analysis, a conversion value of 100% was estimated. The latter value, to be consistent with all other sulfur studies, requires the existence of a completely independent sulfur source which would emit into the atmosphere at a source strength approximately half that measured for DMS under tropical Pacific conditions. At this time, however, there is no credible scientific observation that identifies what this source might be. Thus, the current study has opened for future scientific investigation the major question: is there yet another major tropical marine source of sulfur? Of equal importance, then, is the related question, is our global sulfur budget significantly in error due to the existence of an unknown marine source of sulfur? Pivotal to both questions may be gaining greater insight about the intermediate DMS oxidation species, DMSO, for which rather unusual measurements have been reported in previous marine sulfur studies. The 3 pptv bromine deficit observed in PASE must be lost over the lifetime of the aerosol which is a few days. This observation suggests that the primary BrO production rate is very small. However, considering the uncertainties in these observations and the possible importance of secondary production of bromine radicals through aerosol surface reactions, to completely rule out the importance of bromine chemistry under tropical conditions at this time cannot be justified. This point has been brought into focus from prior work that even at levels of 1 pptv, the effect of BrO oxidation on DMS can still be quite significant. Thus, as in the case of DMS conversion to SO₂, future studies will be needed. In the latter case there will need to be a specific focus on halogen chemistry. Such studies clearly must involve specific measurements of radical species such as BrO.  相似文献   

The Anthropocene: is there a geomorphological case?     

Antony G. Brown  Stephen Tooth  Richard C. Chiverrell  James Rose  David S. G. Thomas  John Wainwright  Joanna E. Bullard  Varyl R. Thorndycraft  Rolf Aalto  Peter Downs 《地球表面变化过程与地形》2013,38(4):431-434

The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’ effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and near‐shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The influence of negatively charged heavy ions on the kinetic Alfven wave in a cometary environment     

Venugopal Chandu  E. Savithri Devi  R. Jayapal  George Samuel  S. Antony  G. Renuka 《Astrophysics and Space Science》2012,339(1):157-164

Kinetic Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of the kinetic Alfven wave in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species was modeled by drifting ring distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution was simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies w^* < w_{cH ⁺}\omega^{*} < \omega_{c\mathrm{H}^{ +}} (ω ^∗ and w_{cH ⁺}\omega_{c\mathrm{H}^{ +}} being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the growth rate increases with increasing negatively charged oxygen ion densities while decreasing with increasing propagation angles, negative ion temperatures and negative ion mass.  相似文献   

Aerosol light absorption, black carbon, and elemental carbon at the Fresno Supersite, California   总被引：2，自引：0，他引：2  

Judith C. Chow  John G. Watson  Prakash Doraiswamy  Lung-Wen Antony Chen  David A. Sodeman  Douglas H. Lowenthal  Kihong Park  W. Patrick Arnott  Nehzat Motallebi 《Atmospheric Research》2009,93(4):874-887

Particle light absorption (b_ap), black carbon (BC), and elemental carbon (EC) measurements at the Fresno Supersite during the summer of 2005 were compared to examine the equivalency of current techniques, evaluate filter-based b_ap correction methods, and determine the EC mass absorption efficiency (σ_ap) and the spectral dependence of b_ap. The photoacoustic analyzer (PA) was used as a benchmark for in-situ b_ap. Most b_ap measurement techniques were well correlated (r ≥ 0.95). Unadjusted Aethalometer (AE) and Particle Soot Absorption Photometer (PSAP) b_ap were up to seven times higher than PA b_ap at similar wavelengths because of absorption enhancement by backscattering and multiple scattering. Applying published algorithms to correct for these effects reduced the differences to 24 and 17% for the AE and PSAP, respectively, at 532 nm. The Multi-Angle Absorption Photometer (MAAP), which accounts for backscattering effects, overestimated b_ap relative to the PA by 51%. BC concentrations determined by the AE, MAAP, and Sunset Laboratory semi-continuous carbon analyzer were also highly correlated (r ≥ 0.93) but differed by up to 57%. EC measured with the IMPROVE/STN thermal/optical protocols, and the French two-step thermal protocol agreed to within 29%. Absorption efficiencies determined from PA b_ap and EC measured with different analytical protocols averaged 7.9 ± 1.5, 5.4 ± 1.1, and 2.8 ± 0.6 m²/g at 532, 670, and 1047 nm, respectively. The Angström exponent (α) determined from adjusted AE and PA b_ap ranged from 1.19 to 1.46. The largest values of α occurred during the afternoon hours when the organic fraction of total carbon was highest. Significant biases associated with filter-based measurements of b_ap, BC, and EC are method-specific. Correcting for these biases must take into account differences in aerosol concentration, composition, and sources.  相似文献   

Spatial and temporal knowledge representation   总被引：1，自引：1，他引：0  

Antony Galton 《Earth Science Informatics》2009,2(3):169-187

Knowledge Representation (KR) originated as a discipline within Artificial Intelligence, and is concerned with the representation of knowledge in symbolic form so that it can be stored and manipulated on a computer. This article surveys that part of KR that is concerned with the representation of space and time, with particular reference to the use of such representations in geographical information science.

Antony GaltonEmail:

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The quartile-deviation/median-diameter relationships of glacial deposits     

Antony T. Buller  John McManus 《Sedimentary Geology》1973,10(2):135-146

Quartile-deviation (QDa) and median-diameter (Md) values have been calculated from the grain-size distributions of a variety of Pleistocene and modern glacial and para-glacial sediments. The QDa—Md pairs are plotted on double-log graph paper to determine whether their graphic distributions are distinctive, and to examine their sedimentological implications. Three distributions emerge. The first has a shallow gradient and represents coarse bi-modal tills consisting largely of rock fragments — distribution (a). The second, with an intermediate gradient, represents fine uni- or non-modal tills consisting mainly of monomineralic grains — distribution (b). The third (c) has a steep gradient and consists of bi-modal tills with a dominant proportion of monomineralic grains. Each of these distributions is explained by using the grain-size characteristics of physically weathered rock debris as a starting point for discussion. By a process dominated by the continual addition of weathered-grain populations (population addition), tills with (a) characteristics are formed. By a process dominated by comminution and the selective removal of grains by ablation (population subtraction), tills with (b) characteristics are formed. Any of these tills, when subjected to flowing water, rapidly lose their glacial characteristics and assume QDa—Md characteristics of fluvial deposits (although they are fluvioglacial).  相似文献   

Topography and ice sheet growth     

Antony Payne  David Sugden 《地球表面变化过程与地形》1990,15(7):625-639

This paper uses a numerical ice sheet model to investigate the role of topography in influencing ice sheet growth. The model is applied to the maritime, mid-latitude uplands of Scotland and relies on a series of assumptions about mass balance, topography, and ice flow. It is driven by an imposed pattern of temperature change. The model is able to predict effectively the extent and thickness of the Loch Lomond ice sheet, using a palaeotemperature curve based on Coleoptera assemblages. A series of experiments with a stepped, constant July air temperature depression suggests that in Scotland a change in excess of ?3·0°C is necessary to initiate ice sheet growth; that steady state ice caps build up at changes of ?3 to ? 6·5°C; and that large ice sheets build up at changes of more than ? 6·625°C. The bifurcation revealed by the last two types of behaviour is the result of topography. Both the vertical amplitude and the spatial distribution of bedrock basins and ridges are important in determining the pattern, rate, and extent of ice sheet growth. The implication is that topography plays an important role in determining the dynamics of ice sheet growth.  相似文献   

In-situ measurements of the aerosol size distributions,physicochemistry and light absorption properties of Arctic haze     

Antony D. Clarke 《Journal of Atmospheric Chemistry》1989,9(1-3):255-266

Thermal and optical techniques were used at Barrow, Alaska during AGASP II (3/20/86–4/7/86) to measure in-situ variability of major aerosol components present in Arctic Haze. The experiment provided continuous data on the concentration, size distribution and relative proportions of sulfate species and refractory aerosol for particle diameters of 0.15 to 5 m. Filter samples were also taken for determination of aerosol optical absorption due to soot (EC-elemental carbon). Although pronounced haze events were absence during this period the haze aerosol present varied in concentration between 2 and 6 g/m³ but showed little change in relative constituents. Apart from local influences, the optical data indicated a persistent fine-mode sulfate aerosol with a NH₄ ⁺/SO₄ ^– molar ratio of about 0.4 and a refractory component of somewhat less than 10% by mass. A preliminary comparison of soot estimates determined from the light absorption data with the size distributions of refractory aerosol observed independently by the optical particle counter showed good agreement during the sample period. In the absence of local pollution, values of single scatter albedo derived from light scattering and light absorption showed similar variation about the average value of 0.86 found by us during flights north of Barrow three years earlier during AGASP I.  相似文献   

Spatio-temporal analysis for monitoring urban growth – a case study of Indore City     

J. Antony Vinoth Kumar  S. K. Pathan  R. J. Bhanderi 《Journal of the Indian Society of Remote Sensing》2007,35(1):11-20

Urban sprawl is characterized by haphazard patchwork of development, which leads to an improper development in any city. To prevent this kind of sprawl in future, it is necessary to monitor the growth of the city. Hence, an attempt has been made in the present study to monitor the urban growth over a period of time by employing Remote Sensing and Geographic Information System techniques in conjunction with Shannon entropy. Shannon entropy is a measure to determine the compactness or dispersion of built-up land growth in the urban areas. The growth patterns of urban built-up land have been studied initially by dividing the area into four zones. The observations have been made with respect to each zone. Then, the study area has been divided into concentric circles of 1 km buffers and the growth patterns have been studied based on urban built-up density with respect to each circular buffer in all four zones. These observations have been integrated with road network to check the influence of infrastructure on haphazard urban growth. It has been found from the study that Shannon entropy is a good measure to determine the spatial concentration or dispersion of built-up land in the city. The study also proved the potential of RS and GIS techniques in the spatio-temporal analysis of urban growth trends and their consequences in the lands adjoining to urban areas.  相似文献