Inversion atmospheric mixing

Heimann M, Kaminski T. 1999. Inverse modelling approaches to infer surface trace gas fluxes from observed atmospheric mixing ratios. In Bouwman AF, ed. Approaches to Scaling of Trace Gas Fluxes in Ecosystems. Amsterdam Elsevier. 

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. 

Taylor and Marsh (7) investigated the long-term characteristics of temperature inversions and mixed layers in the lower atmosphere to produce an inversion climatology for the Los Angeles basin. In this area the cooler ocean currents produce an elevated inversion that is nearly always present and traps the pollutants released over the area within a layer seldom deeper than 1200 m and frequently much shallower. 

Inversion Break-up Fumigation - The inversion break-up screening calculations are based on procedures described in the Workbook of Atmospheric Dispersion Estimates (Turner, 1970). The distance to maximum fumigation is based on an estimate of the time required for the mixing layer to develop from the top of the stack to the top of the plume, using ... 

Mixing height The height above an internal or external pollutant source within which emitted pollutants are dispersed and mixed with the surrounding atmosphere. In meteorological terms, this is the area below the inversion layer. 

The resultant O3 layer is critically important to life on Earth as a shield against LTV radiation. It also is responsible for the thermal structure of the upper atmosphere and controls the lifetime of materials in the stratosphere. Many substances that are short-lived in the troposphere (e.g. aerosol particles) have lifetimes of a year or more in the stratosphere due to the near-zero removal by precipitation and the presence of the permanent thermal inversion and lack of vertical mixing that it causes. 

Figure 2.20 summarizes the role of inversions and the boundary layer in terms of typical changes in mixing of the atmosphere close to the earth s surface at various times of the day (Stull, 1988). At midday, there is generally a reasonably well-mixed convective layer... 

Fig. VIII-4. Nomenclature of the earth s atmosphere based on a temperature classification. The stratosphere is the region of temperature inversion, that is, the temperature increases with height and is stable against vertical mixing since dense cold air is at the bottom of the layer.

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). 

One classic Gaussian plume model for smokestack emissions is the Pas-quill-Gifford model, which applies for steady emissions of a chemical over relatively level terrain. If no chemical sinks exist in the air (i.e., no reactions are degrading the chemical) and if there is an unlimited mixing height (i.e., no atmospheric inversion exists, and the plume can be mixed upward indefinitely), the Pasquill- Gifford model can be expressed in the form... 

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