Atmosphere mixing height

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. 

A few studies reported total PAHs (gas + particle phase) in air in Seoul City during 1999-2002 and found concentrations between 9.10 and 350 ng m-3, with a regional mean of 35.6-89.3 ng m-3 (Park et al., 2002b Kim, 2004). Relatively great concentrations of atmospheric PAHs during winter were ascribed to increased fuel consumption, the lower mixing height and low air temperature. 

Some AQ models rely on standard meteorological products which usually do not include turbulence, atmospheric stability, mixing height, and dispersion coefficients... 

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... 

On the basis of data obtained in the atmosphere Soderlund and Svensson (1976) propose that the atmospheric ammonia burden is 0.9 x 1061 expressed in nitrogen. For the calculation of this figure the authors mentioned assumed characteristic mixing heights for different climatic regions. This height varied between 1 and 2 km. 

Here, H = 8500 m denotes the atmospheric scale height. Radon obviously would be a good tracer for turbulent mixing in the troposphere. Unfortunately, it is hard to measure. It should be noted that the assumption of a constant Kz in the troposphere is a reasonable approximation only for the region outside the planetary boundary layer (zs=2km). The air motions close to the earth surface are greatly influenced by friction, which causes the eddy coefficients to decrease from their values in the free troposphere. 

I Urban SOz SO2 is emitted in an urban area with a flux of 2000 pg m 2h-1. The mixing height over the area is 1000 m, the atmospheric residence time 20 h, and SO2 I reacts with an average rate of 3% h-1. Rural areas around the city are characterized I by a SO2 concentration equal to 2 pg m-3. What is the average SO2 concentration in I the urban airshed for these conditions Assume an SO2 dry deposition velocity of I 1 cm s l and a cloud/fog-frec atmosphere. ... 

Mixing height is an important parameter as it governs not only vertical dilution of the pollutant but also horizontal dilution by wind shear effects. Unstable air masses normally have a deeper and more active mixing layer than stable air masses. Thus plumes emitted into a stable atmosphere undergo little vertical or horizontal diffusion and can travel intact for several hundred kilometres before being dispersed or incorporated into cloud. Figure 3.5(c) shows such a narrow, coherent plume observed by satellite over Ontario, Canada. 

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