Maximum ground level concentration

Maximum Ground-Level Concentrations The effective height of an emission having been determined, the next step is to study its path downward by using the appropriate atmospheric-dispersion formula. Some of the more popular atmospheric-dispersion calculational procedures have been summarized by Buonicore and Theodore (op. cit.) and include ... 

Fig. 20-1. Concentration of an air pollutant at the point of maximum ground-level concentration as a function of wind speed and Pasquill stability category (A-F).

Maximum ground level concentration and its location can be calculated from the following expression ... 

The values of u and A0/AZ are based on assumed conditions of stability class F and stack height wind speed of 2.5 m/s for the stable layer above the inversion. The value of hj incorporates the effect of buoyancy induced dispersion on a/, however, elevated terrain effects are igndred. The equation above is solved by iteration, starting from an initial guess of x , = 5,000 m. The maximum ground-level concentration due to inversion break-up fumigation, Xf, is calculated from ... 

As with the inversion break-up case, the distance to maximum ground-level concentration is determined by iteration. The equation used for the shoreline fumigation case is ... 

The maximum ground-level concentration due to shoreline fumigation, Xf. is calculated from ... 

Table 2. Maximum Ground Level Concentration for A 5-min. Blow (Worst Case)...

Maximum ground level concentrations estimated from the (episode) case condition assumed herewith within close proximity of the plant (up to 5-miles) range as follows ... 

Tables 9 and 10 give the maximum ground level concentrations expected for worst case conditions for the 3-min. and 5-min. venting rates, respectively worst case conditions were obtained from Tables 7 and 8 (i.e., values were calculated based on the largest concentration found in Tables 7 and 8 for each distance within a stability class).

The maximum ground-level concentration calculated on a 10-minute basis for no nuisance should therefore be equal to the detection threshold, i.e. 

The maximum ground-level concentration along the x axis (C)max is found using... 

The distance downwind at which the maximum ground-level concentration occurs is found from... 

From equation (3.13) we can deduct a rough approximation of the location where maximum ground-level concentration occurs. It is argued that the turbulent diffusion acts more and more on the emitted substances, when the distance from the point source increases therefore the downwind distance dependency of the diffusion coefficients is done afterwards. If we drop this dependency, equation (3.13) leads to xmax=34,4 m for AK=I (curve a) and xmax=87,7 m for AK=V (curve b), what is demonstrated in fig n The interpolated ranges of measured values are lined in. Curve a overestimates the nondimensional concentration maximum, but its location seems to be correct. In the case of curve b the situation is inverted. Curve c is calculated with the data of AK=II. The decay of the nondimensional concentration is predicted well behind the maximum. Curve d is produced with F—12,1, f=0,069, G=0,04 and g=l,088. The ascent of concentration is acceptable, but that is all, because there is no explanation of plausibility how to alter the diffusivity parameters. Therefore it must be our aim to find a suitable correction in connection with the meteorological input data. 

As a rule of thumb, with stacks between about 15 and 100 m (50 and 350 ft) tall, this point of maximum concentration will be approximately 10 stack heights downwind. Therefore, the air-quality monitoring system should include at least one sensor at the point of expected maximum ground-level concentration. Additional sensors should be placed not less than 100 stack heights upwind (prevailing) to provide a background reading, and at least... 

Estimate the maximum ground-level concentration in grams per cubic meter. Use the approximation formula C = 0.23Q/U(H )2, where C is in grams per cubic meter, Q is in grams per second, U is in meters per second, and // is in meters. Thus,... 

When material is emitted from a single elevated stack, the resulting ground-level concentration exhibits maxima with respect to both downwind distance and windspeed. Both directly below the stack, where the plume has not yet touched the ground, and far downwind, where the plume has become very dilute, the concentrations approach zero therefore a maximum ground-level concentration occurs at some intermediate distance. Both at very high wind speeds, when the plume is rapidly diluted, and at very low... 

To investigate the properties of the maximum ground-level concentration with respect to distance from the source and windspeed, we begin with the Gaussian plume equation evaluated along the plume centerline (y = 0) at the ground (z = 0) ... 

We want to calculate the location xm of the maximum ground-level concentration for any given wind speed. By differentiating (18.117) with respect to x and setting the resulting equation equal to zero, we find... 

Now we consider the effect of wind speed u on the maximum ground-level concentration. The highest concentration at any downwind distance can be determined as a function of u. Differentiating (18.A. 11) with respect to u, we obtain... 

One way to quickly determine the stability of the lower atmosphere is to view the shape of a smoke trail, or plume, from a tall stack located on flat terrain. Visible plumes usually consist of pollutants emitted from a smoke stack into the atmosphere. The formation and fate of the plume itself depend on a number of related factors (1) the nature of the pollutants, (2) meteorological factors (combination of vertical air movement and horizontal air flow), (3) source obstructions, and (4) local topography, especially downwind. Overall, maximum ground-level concentrations will occur in a range from the vicinity of the smokestack to some distance downwind. 

The effective chimney height,/f, is made up of two components. It is the sum of the actual chimney height and the plume rise, the latter being the additional height to which the plume centre-line ascends due to its buoyancy and efflux velocity. Examination of curves in which the maximum ground-level concentration is plotted as a function of H and atmospheric stability show that x is... 

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