Air motion

Vertical air motions affect both weather and the mixing processes of importance to air pollution. Upward vertical motions can be caused by lifting over terrain, lifting over weather fronts, and convergence toward low-pressure centers. Downward vertical motions can be caused by sinking to make up for divergence near high-pressure centers. One must know whether the atmosphere enhances or suppresses these vertical motions to... 

At times the ventilation rate becomes very low. Such a lack of air motion usually occurs in the weak pressure gradient near the center of an anticy-... 

Active generation into zone of rapid air motion Spray painting in shallow booths Barrel filling Conveyor loading Crushers 1.02-2.54... 

In another case, when the air motion results in a temperature rise, the density of the air sphere is less than the surroundings, and the sphere of air continues... 

Conditions that are warmer than the applicable still-air comfort zone of Fig. 5.7b can often be made comfortable by increasing the air speed. If the conditions are 1 to 6 °C warmer than the still-air comfort zone of Fig. 5.7b, the necessary air speed v) to restore thermal balance and comfort can be estimated from Fig. 5.8, where Tis the temperature difference between the environment and the still-air comfort temperature. Though the increased air speed will bring the whole-body thermal sensation to the comfort level, air motions above 0.8 m/s or so may cause other kinds of discomfort frojn... 

Local air motion is another thermal nonuniformity that can cause a local cooling of the skin and the feeling of a draft. Draft discomfort from local air motion increases as the air temperature decreases below skin temperature. Fluctuations in the local air motion increase the perception of drafts and should be avoided. The unsteadiness of air motion is often described in terms of its turbulence intensity (Tu) ... 

Mierzwinski, S. 1981. Air motion and temperature distribution above a human body as a result of natural convection. A4-serien no. 45, Inst, for EIppv.- o Vent, teknik, KTH, Stockholm. 

Furthermore, winds at an angle to the building side will have downward air motions above the roof and downwind of the building, which also will increase rooftop concentrations. 

Exterior hoods intended to capture contaminants should be placed as close to contaminant sources as possible. In actual practice, however, the hoods can not always be placed close to the source due to circumstances such as working conditions. In such cases, to enhance the exhaust efficiency of exterior hoods, it is useful to use a low-momentum air supply directed toward the exhaust outlet. The supply airflow, which functions to transport contaminants emitted from sources located at a distance from the exhaust outlet,. should be relatively low with a uniform velocity but high enough so that it is not disturbed by the. surrounding air motions. The advantages of using low-momentum supply with exterior hoods are that (1) a lower supply airflow rate to the workspace is possible, (2) a lower exterior hood exhaust flow rate is possible, and (3) it is possible to supply clean air to the breathing zone of the worker. 

Gases, vapors, and fumes usually do not exhibit significant inertial effects. In addition, some fine dusts, 5 to 10 micrometers or less in diameter, will not exhibit significant inertial effects. These contaminants will be transported with the surrounding air motion such as thermal air current, motion of machinery, movement of operators, and/or other room air currents. In such cases, the exterior hood needs to generate an airflow pattern and capture velocity sufficient to control the motion of the contaminants. However, as the airflow pattern created around a suction opening is not effective over a large distance, it is very difficult to control contaminants emitted from a source located at a di,stance from the exhaust outlet. In such a case, a low-momentum airflow is supplied across the contaminant source and toward the exhaust hood. The... 

In the low-momentum supply system, the contaminants are emitted within the low -momentum airflow blown from the supply inlet and they are transported to near the exhaust opening. If the contaminants diffuse into the whole of the supply airflow, the exterior hood must exhaust the whole of the airflow. To diminish the exhaust flow rate, some methods to prevent the contaminants from diffusing into the whole of the airflow are required. One possible method is to supply the air as slowly as possible but with enough velocity to reach the exhaust outlet and to control the surrounding air motion. Another method is to blow supply air with uniform... 

Chen, Q. Prediction of room air motion by Reynolds-stress models. Build. FInviron., vol. 31, pp. 233-244, 1996. 

Wind Air motion relative to the earth s surface caused by thermal forces and the earth s rotation. 

Some particles and fibers may be generated by indoor equipment (e.g. copy machines and printers). Mechanical abrasion and air motion may cause particle release from indoor materials. Particles are also produced by people, e.g., skin flakes are shed and droplet nuclei are generated from sneezing and coughing. Some particles may contain toxic chemicals. 

Released at high initial velocity into zone of very rapid air motion Grinding Abrasive blasting Tumbling 2.54-10.2... 

Sound hearing 5xl09 years ago ears Air motion other organisms... 

Rudnick, S.N., W.C. Hinds, E.F. Maher, and M.W. First, Effect of Plateout, Air Motion and Dust Removal on Radon Decay Product Concentration in a Simulated Residence, Health Phvs. 45 463-470... 

Figure 5-3 Air temperature as a function of altitude for day and night conditions. The temperature gradient affects the vertical air motion. Adapted from D. Bruce Turner, Workbook of Atmospheric Dispersion Estimates (Cincinnati US Department of Health, Education, and Welfare, 1970), p. 1.

The reaction sequence (8.156)-(8.157) is a catalytic chain for ozone destruction and contributes to the net destruction. However, even given the uncertainty possible in the rates of these reactions and the uncertainty of the air motions, this system could not explain the imbalance in the ozone throughout the stratosphere. 

Meteorological Of changes in the temperature, humidity, or air motion of the atmosphere. 

There is also a significant correlation between temperature fluctuations in the lower stratosphere and fluctuations in total ozone. There are two sources of this correlation, radiative and dynamical (McCormack and Hood, 1994). Thus, increased ozone leads to increased absorption of solar radiation and increased heating. In addition, dynamical effects associated with vertical and meridional air motions also give a positive correlation between ozone and stratospheric temperature. For example, Randel and Cobb (1994) analyzed total column 03 and temperatures in the lower stratosphere from 1979 to 1992. Correlations between 03... 

At low-discharge velocities and low film thicknesses, the sheet disintegration is due to the oscillations caused by air motion. In this case, the film thickness has a large impact on the droplet size. In contrast, it is insignificant whether a pure liquid or a lime-water suspension (mass portion cj) = 16-64%) is treated (21). 

Since the production rates of the cosmic ray radionuclides increase rapidly with increasing altitude in the lower atmosphere, the atmospheric concentrations and ratios of short lived cosmic ray radionuclides can be used to study rapid vertical air motions if the equilibrium concentrations of the radionuclides are known. For example, the concentrations of the short lived cosmic ray radionuclides in air which has moved upward recently from a lower altitude will be less than the equilibrium concentrations. The concentrations of the radionuclides will therefore increase with time until equilibrium is reached. However, the concentration of the shorter lived of two short lived radionuclides will increase more rapidly initially, causing the ratio of the two radionuclides of different half-lives to change with time until equilibrium is reached. Therefore, the time since the air moved from a lower altitude, the speed of the upward motion, and the altitude from which the air originated could be calculated from the concentrations and concentration ratios of cosmic ray radionuclides of different half-lives. Vertical motions of different speeds could be studied since several cosmic ray radionuclides of different half-lives are present in the atmosphere (Table I). Many other radionuclides are produced by cosmic rays in the atmosphere, but they have not yet been detected. Some of these with half-lives of a few minutes could serve as tracers of very short term processes such as post-nucleation scavenging. 

The technique requires simultaneous fast and accurate measurements of both the vertical velocity and the trace species in question. Fortunately the technology for the measurement of turbulence with the necessary resolution is available. Sonic anemometers can readily yield air motion data with the required resolution (10). Likewise, the ability to handle the air motion and chemical concentration data with modern computer data systems is well in hand (II). Thus these aspects can be ignored, and the major limitation can be dealt with the availability of appropriate chemical sensors with sufficient time and chemical resolution. 

The most obvious result of ducting the atmospheric sample from the vicinity of the sonic anemometer to the chemical sensor is the introduction of a time delay. This time lag must be eliminated before the correlation between chemical concentration and the vertical air motion variances is made to yield the covariance. Several different approaches have been taken to determine the length of the delay. One simple method involves spiking a balloon with the compound involved, and then inflating and bursting it in such a manner that the sonic anemometer path is interrupted at the same... 

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