Stable atmosphere

From the viewpoint of air pollution, both stable surface layers and low-level inversions are undesirable because they minimize the rate of dilution of contaminants in the atmosphere. Even though the surface layer may be unstable, a low-level inversion will act as abarrier to vertical mixing, and contaminants will accumulate in the surface layer below the inversion. Stable atmospheric conditions tend to be more frequent and longest in persistence in the autumn, but inversions and stable lapse rates are prevalent at all seasons of the year. 

If the sphere of air mass moves upward in an adiabatic process but in an atmosphere with a subadiabatic lapse rate, the sphere follows a temperature change given by the adiabatic slope but when it arrives at point Zj, it is at a lower temperature than its surroundings, but at the same pressure. As a result, it is heavier than the surroundings and tends to fall back to its original position. This condition is called stable. In a stable atmosphere pollutants will only slowly disperse, and turbulence is suppressed. 

The running of a cool airflow under a warm wind is another cause of temperature inversion. As a rule, the presence of an inversion implies a highly stable atmosphere one in which vertical air movements is rapidly damped out. In such a situation, fog and airborne pollutants collect, being unable to move freely or be dissipated by convection. 

Short. Vapor may persist for some time in low places under calm or light winds and stable atmospheric conditions. 

A stable atmosphere saturated with the vapour of the mobile phase is required to ensure reproducible Rt values. Unless saturation conditions prevail, solvent will evaporate from the surface of the thin layer causing an increased solvent flow but slower movement of the solvent front f f values consequently increase. In practice, chromatograms are best developed in a sealed glass tank in which a saturated atmosphere has been produced by... 

Hilst, G. R. (1957). Observations of the diffusion and transport of stack effluents in stable atmospheres. Ph.D. Thesis, University of Chicago, Chicago, Illinois. 

Stable aerosol generation is important to maintain a stable atmosphere in the chamber. Good stability of the aerosol size distribution and mass output was observed for Pb aerosol over... 

Consider now at the environmental conditions of temperature T0 and pressure ft a gas mixture whose compositional values xl are different from those values xi 0 of the stable atmospheric air. For this stable atmospheric air each of the partial molar exergy values of the constituents are zero. From Eq. 10.23 we then obtain the exergy of the gas mixture as shown inEq. 10.24 ... 

Heavy-gas effects at the source are more important if the cloud s potential energy is larger than the turbulent kinetic energy generated by the surrounding air. Therefore, heavy-gas effects are more important at low wind speeds and stable atmospheric conditions than at high wind speeds and neutral or unstable atmospheric conditions. 

In this problem, a standard pan is used as shown in Fig. 11-6. The mean wind movement is measured 6 in above the pan rim, and water-evaporation rates are measured with the pan placed on the ground (land pan) or in a body of water (floating pan). For the land pan and with a convectively stable atmosphere, the evaporation rate has been correlated experimentally [13] as... 

As just indicated, wind speed can increase approximately logarithmically with distance above a plant canopy (Fig. 9-1) and is also influenced by properties of the plants. In particular, the variation in wind speed v with distance above a large, horizontal, uniform canopy under stable atmospheric conditions can be described by... 

Inversion— An atmospheric condition in which air temperature increases with increasing altitude, instead of the usual decrease. The occurrence of a temperature inversion causes stable atmospheric conditions beneath, which can result in an accumulation of air pollutants if emissions continue during the inversion event. 

Because stability is affected by the SST, it is noteworthy that the lowest dependence of salt loads on wind speed occurred during Interval 4 (when the SST values were lowest). In the mean, most likely stable atmospheric conditions exist with lower sea surface temperatures. 

FIGURE 4-6a A stable atmosphere. The actual, measured temperature profile of the atmosphere decreases at a rate less than the adiabatic rate. Thus, when this air parcel is pushed upward, perhaps by an eddy in a turbulent atmosphere, it finds itself in warmer, and hence less dense, surroundings being cooler and denser it sinks back down. This stable situation tends to suppress vertical mixing. 

FIGURE 4-10 Emission of pollutants from a smokestack, a typical continuous source, under a variety of meteorological conditions. The dry adiabatic lapse rate is represented as a dashed line and the actual measured lapse rate as a solid line in the left panels. Vertical mixing is strongest when the adiabatic lapse rate is less than the actual measured lapse rate and the atmosphere is unstable (top). Weak lapse is a term used to express the existence of a stable atmosphere, which results in less vigorous vertical mixing. An inversion, in the third panel from the top and in part of the last three panels, results in a very stable atmospheric layer in which relatively little vertical mixing occurs (Boubel et al, 1994). 

Coen and Clark [128] has coupled a fire model into a three-dimensional non-hydrostatic terrain-following numerical mesoscale model developed at the US National Center for Atmospheric Research, Boulder, CO. The model includes rain and cloud physics. Calculations predict the growth and spread of a fire line moving across a two dimensional small Gaussian hill (height 200 m, half-width 300 m) for a wind speed of 3 m/s, and a stable atmospheric lapse rate (10°C/km). The head of the fire propagated quickly uphill in the direction of the environmental wind. Once the fire reaches the top of the hill, the updrafts tend to inhibit the forward movement of the fire front, and the fire spreads faster laterally in the lee of the hill. 

Temperature inversion In a temperature inversion, the potential temperature of the atmosphere increases with increasing height, creating a stable atmosphere in which vertical motion is suppressed. 

The results are shown in Fig. 1. In this calculation, a neutrally stable atmosphere with Tair = Tsea = 10 °C is used, and the wave age is set at 25. No slicks are used. (In the standard VIERS-1 spectrum, a wind-dependent slick coverage is assumed.) The integration over the saturation range gives rise to a flat curvature spectrum, as it should, and the overall shape of the spectra is practically identical to the original VIERS-1 form. 

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