Temperature potential

A concept that is very useful in relating meteorological conditions to the mixing and transport of air pollutants is that of potential temperature. Potential temperature (9) is defined as the temperature an air parcel of temperature T and pressure P would have if it were expanded or compressed under adiabatic conditions to some reference pressure P ). 

Adiabatic expansion or compression of an air mass maintains a constant potential temperature. From the definition of entropy, S, as dS = dqKV/T, these processes are also constant-entropy processes since no heat is exchanged between the system (i.e., the air parcel) and its surroundings. Hence the term isen-tropic is used to describe processes that occur without a change in potential temperature. 

Potential temperature is a very useful parameter in several ways. First, air pollutants or trace gases within an air parcel having a constant value of 6 can be assumed to be well mixed within that air parcel. Thus only limited numbers of measurements within the parcel are necessary to characterize its composition. 

Second, air parcels tend to conserve their potential temperature i.e., air parcels tend to move along lines of constant 9. Thus the potential temperature becomes a sort of tracer for the history of air parcels. 

Let us assume that an air parcel somewhere in the atmosphere has a temperature T and pressure p and is initially in equilibrium (same Tand p) with the surrounding atmosphere. If this air parcel is moved dry adiabatically to the surface with a pressure of po = 1000 mbar, it will attain a temperature 9 called the potential temperature. The potential temperature can be calculated from (16.5) integrating from initial conditions (T,p) to the final state (0,po) to find that 

For p = po the potential temperature is equal to the surface temperature To. and the potential temperature profile of the atmosphere starts at the surface temperature. The potential temperature is used in meteorology to compare the temperature of air parcels under identical conditions. As we will see subsequently, it is also useful in the stability analysis of the atmosphere. 

If the adiabatic dry air parcel is always in equilibrium with the atmosphere during its motion from the original position to the surface, the atmosphere by definition is neutral and its temperature profile satisfies (16.8). No matter where the air parcel starts in this atmosphere, it will always attain the same temperature when brought to the surface at pressure po- In other words, the potential temperature of the air parcel will not change during its motion and will always be equal to 0. The equilibrium of the air parcel with the surrounding environment means that the neutral atmosphere (or a neutral atmospheric layer) has the same potential temperature at all heights z and therefore dQ/dz = 0. Plots of altitude versus potential temperature for a neutral (adiabatic) atmosphere are vertical lines at 0 = 7b. 

The results described above can be demonstrated mathematically by differentiating (16.14) with respect to z to get 

Replacing (1.3) for dp/dz and simplifying, recognizing that V = g/cp, we find that 

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What is the potential temperature rise by the desired reaction What is the rate of the temperature rise Enthalpy of desired reaction Specific heat Table of data Thermodynamic data Calculations estimations... 

What is the potential temperature rise by undesired reactions or thermal decomposi- tion, such as from contaminants, impurities, etc. What are the consequences What is the maximum pressure Enthalpy of undesired reaction Specific heat Rate of undesired reaction as a function of temperature DTA/DSC Dewar flask experiments APTAC /ARC /RSST/VSP... 

A useful concept in determining stability in the atmosphere is potential temperature. This is a means of identifying the dry adiabat to which a particular atmospheric combination of temperature and pressure is related. The potential temperature 0 is found from... 

If the potential temperature decreases with height, the atmosphere is unstable- If the potential temperature increases with height, the atmosphere is stable. The average lapse rate of the atmosphere is about 6.5°C/km that is, the potential temperature increases with height and the average state of the atmosphere is stable. 

Briggs For unstable and neutral conditions Ah = 0.25Qh" hp U For stable conditions Ah = 0.296[Q /U(ae/az] where 56/5z = variation of potential temperature with height = 0.03 K/m Nonempirical formulation... 

A0/AZ = vertical potential temperature gradient (assume 0.035 K/m for F stability)... 

Potential temperature The temperature an air envelope would acquire if brought adiabatically from its initial or actual pressure to a standard pressure of 1000 mb. 

Stability Type Potential Temperature Lapse Rate, (K/lOO m) AG/Az... 

The Kolmogorov velocity field mixes packets of air with different passive scalars a passive scalar being one which does not exchange energy with the turbulent velocity flow. (Potential) temperature is such a passive scalar and the temperature fluctuations also follow the Kolmogorov law with a different proportionality constant... 

Fig. 14-6 Profiles of potential temperature and phosphate at 21 29 N, 122 15 W in the Pacific Ocean and a schematic representation of the oceanic processes controlling the P distribution. The dominant processes shown are (1) upwelling of nutrient-rich waters, (2) biological productivity and the sinking of biogenic particles, (3) regeneration of P by the decomposition of organic matter within the water column and surface sediments, (4) decomposition of particles below the main thermocline, (5) slow exchange between surface and deep waters, and (6) incorporation of P into the bottom sediments.

A thorough insight into the comparative photoelectrochemical-photocorrosion behavior of CdX crystals has been motivated by the study of an unusual phenomenon consisting of oscillation of photocurrent with a period of about 1 Hz, which was observed at an n-type CdTe semiconductor electrode in a cesium sulfide solution [83], The oscillating behavior lasted for about 2 h and could be explained by the existence of a Te layer of variable width. The dependence of the oscillation features on potential, temperature, and light intensity was reported. Most striking was the non-linear behavior of the system as a function of light intensity. A comparison of CdTe to other related systems (CdS, CdSe) and solution compositions was performed. 

Draw the concentration and flux profiles of a species i with surface concentration of 2 and bottom concentration of 10 (arbitrary units). Assume that the mixing length can be obtained from the distribution of conservative quantities, usually salinity or potential temperature. Craig (1969) suggests a value of 800m in the 4000m-deep Pacific. 

The interfacial microenvironment around a microbial community, that is the sum of the physical, chemical, and biological parameters which affect a microorganism, determines whether a particular microorganism will survive and/or metabolize. The occurrence and abundance of microorganisms in an environment are determined by nutrient availability, and various physicochemical factors such as pH, redox potential, temperature, and solid phase texture and moisture. Because a limitation imposed by any one of these factors can inhibit biodegradation, the cause of the persistence of a pollutant is sometimes difficult to pinpoint. The summary follows [39,92,94,97,109,110,172,173,176,189,190, 195,248-252,256-300]. 

Table L Mean values of redox potential, temperature, residence time, pH and DO in the twelve treatments (standard deviations are shown in parentheses).

It is not simple to give a measure of the resistance to pitting of a particular stainless steel, because it depaids on many factors associated with the actual environment. The three main factors are potential, temperature, and concentration of initiating ions. 

In the early 1970s, Brigham and Tozer were the first to make a systematic study, using temperature as the variable, of the connection between potential, temperature, and pitting corrosion (Fig. 12). They argued that in principle a critical pitting temperature should exist, but the data obtained showed a transition over a range of temperatures. The sharp transition was demonstrated experimentally by Quarfort in 1989. 

Over the years different researchers have investigated the relationships between potential, temperature, and concentration of activat-... 

Generally, a continuous recording of electrically available data - for example, current, cell voltage, electrode potentials, temperatures - is beneficial to supervise the proper procedure of each experiment. Especially in case of a failure this will be a valuable help to find the reason. Today, the best way is to use a data acquisition system in a computer that offers the results directly for further calculations, for example, integration of the consumed current (converted charge). For continuously operated experiments the addition of scales, which acquire the weight of input and output reservoirs, will be advantageous in order to supervise the mass balances continuously. 

Velocity and temperature gradients are confined to the surface layer defined by z < I-. Above L the wind velocity and potential temperature are virtually uniform with height. Venkatram (1978) has presented a method to estimate the value of the convective velocity scale w,. On the basis of this method, he showed that convective conditions in the planetary boundary layer are a common occurrence (Venkatram, 1980). In particular, the planetary boundary layer is convective during the daytime hours for a substantial fraction of each year ( 7 months). For example, for a wind speed of 5 m sec , a kinematic heat flux Qo as small as O.PC sec can drive the planetary boundary layer into a convective state. 

Site geochemistry must ensure conditions appropriate for the reduction of contaminant concentrations (e.g., the presence of mineral nutrients and electron acceptors, and the correct redox potential, temperature, and pH). 

Longitudinal profiles in the Atlantic Ocean at about 25°W. (a) Potential temperature (°C), (b) salinity, (o) potential density (0 dbar), (d) potential density (4000 dbar), and (e) dissolved oxygen ( j,mol/kg). Source-. After Talley, L. (1996). Atlantic Ocean Vertical Sections and datasets for selected lines. http /sam.ucsd.edu/vertical.sections/Atlantic.html. Scripps Institute of Oceanography, University of California - San Diego. Data are from WOCE hydrographic program. (See companion website for color version.)... 

Empirical equations have been formulated to enable calculation of the Bimsen solubility coefficient for any given temperature and salinity at = 1 atm. These empirical equations are presented in the online appendix on the companion website for the most common gases foimd in seawater but being empirical, they are still subject to refinement. The equilibrium gas concentrations computed from the Bimsen solubility coefficient should be thought of as the gas concentration that a water mass would attain if it were allowed to equilibrate with the atmosphere at its in situ salinity and potential temperature. 

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