Atmospheric composition, transport

Meridional circulation in two-dimensional stratospheric models has been specified based on observations or general circulation model calculations recendy efforts have been undertaken to calculate circulations from first principles, within the stratospheric models themselves. An important limitation of using models in which circulations are specified is that these caimot be used to study the feedbacks of changing atmospheric composition and temperature on transport, factors which may be important as atmospheric composition is increasingly perturbed. 

The meteorological conditions during PAUR II were favourable for the study of the background atmospheric composition in the region. N/NE and W/NW flow was alternated with SW flow that transported air from the Sahara. Hence, the chemical, physical and optical characteristics of the background Eastern Mediterranean atmosphere were studied for the first time for a variety of synoptic flows. 

The results presented here focus on the present and future effect on radiative forcing due to changes in the radiatively-important chemical species (03, water vapor and CHJ associated with aircraft emissions. To address this question, we conduct uncoupled model experiments using the University of Oslo (UiO) 3-D chemical transport models (CTMs) to calculate changes in atmospheric composition and the State University of New York at Albany (SUNYA) 3-D global climate model (GCM) to calculate the radiative forcing associated with these changes. Two case studies were conducted to... 

A two-step process, involving the production of fine metallic particles followed by their oxidation, has been used to synthesize oxide powders with sizes smaller than a few tens of nanometers (102,103). In the process, a metal (e.g., Ti) is evaporated into an inert atmosphere (e.g.. He) with pressure of —100 Pa. The particles that condense in the inert atmosphere are transported by convective gas flow to a cold shroud where they adhere. Oxygen gas at a pressure of —5 kPa is then admitted to the chamber to produce oxidation of the metal particles. The particles are finally scraped off the cold shroud and collected. Starting with Ti, this process produces a highly oxygen deficient oxide TiOi,7 with the ratile stmcture, but subsequent heating at —300°C produces a nearly stoichiometric composition, TiOi.gs. 

Acid deposition refers to the transport of acid constituents from the atmosphere to the earth s surface. This process includes dry deposition of SO2, NO2, HNO3, and particulate sulfate matter and wet deposition ("acid rain") to surfaces. This process is widespread and alters distribution of plant and aquatic species, soil composition, pH of water, and nutrient content, depending on the circumstances. 

Airborne particulate matter, which includes dust, dirt, soot, smoke, and liquid droplets emitted into the air, is small enough to be suspended in the atmosphere. Airborne particulate matter may be a complex mixture of organic and inorganic substances. They can be characterized by their physical attributes, which influence their transport and deposition, and their chemical composition, which influences their effect on health. The physical attributes of airborne particulates include mass concentration and size distribution. Ambient levels of mass concentration are measured in micrograms per cubic meter (mg/m ) size attributes are usually measured in aerodynamic diameter. Particulate matter (PM) exceeding 2.5 microns (/i) in aerodynamic diameter is generally defined as coarse particles, while particles smaller than 2.5 mm (PMj,) are called fine particles. 

In a permeation experiment, an HERO module with a membrane area of 200 m is used to remove a nickel salt from an electroplating wastewater. TTie feed to the module has a flowrate of 5 x IQ— m /s, a nickel-salt composition of 4,(X)0 ppm and an osmotic pressure of 2.5 atm. The average pressure difference across the membrane is 28 atm. The permeate is collected at atmospheric pressure. The results of the experiment indicate that the water recovery is 80% while the solute rejection is 95%. Evaluate the transport parameters Ay and (D2u/KS). 

Variations in solution composition throughout a test should be monitored and, if appropriate, corrected. Variations may occur as a result of reactions of one or more of the constituents of the solution with the test specimen, the atmosphere or the test vessel. Thus, it is important that the composition of the testing solution is what it is supposed to be. Carefully made-up solutions of pure chemicals may not act in the same way as nominally similar solutions encountered in practice, which may, and usually do, contain other compounds or impurities that may have major effects on corrosion. This applies particularly to artificial sea-water, which is usually less corrosive than natural sea-water. This subject is discussed in detail in a Special Technical Publication of ASTM, and tests with natural, transported and artificial sea-water have been described . Suspected impurities may be added to the pure solutions in appropriate concentrations or, better still, the testing solutions may be taken directly from plant processes whenever this is practical. 

It is remarkable that, except for local hot-spots such as around industrial sites, mining areas and volcanoes, the elemental compositions of atmospheric dust in similar locations, such as remote or rural or urban are relatively constant over the world. This suggests either common sources, or a dominant source, or good mixing and transport of the dust around the globe. In fact all three factors have a role in determining the uniformity. Because of the consistent composition it is possible to estimate the median concentrations of the elements in atmospheric dusts in similar, but widely separated, locations. These estimates are given in columns 2 to 7 in Table n. The concentrations of the elements in the atmospheric dust are expressed as mass per volume of air. For remote locations (columns 2 to 5) the concentrations are in ng m 3, whereas for rural and urban areas (columns 6 and 7) the elemental concentrations are in xg m-3. 

Despite the difficulties, there have been many efforts in recent years to evaluate trace metal concentrations in natural systems and to compare trace metal release and transport rates from natural and anthropogenic sources. There is no single parameter that can summarize such comparisons. Frequently, a comparison is made between the composition of atmospheric particles and that of average crustal material to indicate whether certain elements are enriched in the atmospheric particulates. If so, some explanation is sought for the enrichment. Usually, the contribution of seaspray to the enrichment is estimated, and any enrichment unaccounted for is attributed to other natural inputs (volcanoes, low-temperature volatilization processes, etc.) or anthropogenic sources. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

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