Prof. Jiakuan Yang Huazhong University of Science and Technology Air Pollution Control Engineering

Lecture 6 Air Pollutant Concentration Models Ⅰ What is Air pollutant Concentration Model? Ⅱ Fixed-box model Ⅲ Gaussian Diffusion Model Ⅳ Other topics about Air pollutants transporting Ⅴ Summary

(4) Gaussian plume, two-dimensional spreading equation ②

The first term is the concentration on the centerline of the plume. ③ three terms of Gussian plume equation  First term, when y = 0, ( z – H) = 0, so exp 0 = 1 With the increase of downwind distance(x), c on centerline is decreasing.

(4) Gaussian plume, two-dimensional spreading equation Second term < 1 c The second term shows how the concentration decreases as we move in the horizontal. Diffusion in y direction.

(4) Gaussian plume, two-dimensional spreading equation Third term Diffusion in z direction. The same as the second term. y Z x y Z

沿着 Z 方向的正态分布

(4) Gaussian plume, two-dimensional spreading equation downwind distance Page 135, Figure 6.7 Page 136, Figure 6.8, would depend on wind speed, and on the degree of atmospheric turbulence, degree of solar heating.

Page 135, Figure 6.7 Page 136, Figure 6.8

(5) Gaussian plume equation considering reflection effect of the ground H -H

(5) Gaussian plume equation considering reflection effect of the ground

(6 ) ground-level concentration when z = 0

Ⅳ Other topics about Air pollutants transporting (1) Building wakes( 建筑物尾迹 ) A plume may get sucked into the low pressure wake behind a building, leading to a high local concentration. The simple rule of thumb for avoiding.This problem is to make the stack height at least 2.5 times the height of the tallest nearby building.

Ⅳ Other topics about Air pollutants transporting (2) Aerodynamic down wash （空气下洗区） When the stack is located near a mountain, the simple Graussian plume equations will not be applied. The ground-level concentrations from stack where certainly many times what would be calculated with the simple ( flat world ) Graussian plume equations.

Ⅴ Summary (1) Fixed-box models – qualitatively Gaussian plume models – point sources, quantitatively

Ⅴ Summary 2) Gaussian plume models are applied in Flat terrain The instantaneous meteorology is simple Not work in Mountainous country Nor for long distance Nor at times when the meteorology is complex

Ⅴ Summary (3) Building wakes, local mountains, and other sources of air flow perturbations complicate air pollution models.

Ⅴ Summary The Gaussian plume diffusion model there are three important equations for Gaussian plume, two- dimensional spreading. (1) Basic Gaussian plume equation

Ⅴ Summary (2) Basic Gaussian plume equation modified by effect of the ground (3) Ground-level concentration equation

Example 6.4 A factory emits 20g/s of SO 2 at height H. Wind speed is 3m/s. At a distance of 1km downwind, the values of σ y and σ z are 30m and 20m,respectively. What are the SO 2 concentrations at the centerline of plume,and at a point 60 meters to the side of the centerline and 20 meters below the centerline. At centerline, x = 1000m, y =0, z = H σ y =30m, σ z = 20m u =3m/s, Q = 20 g/s

Example 6.4 = 1770μg/m 3

Example 6.4 At the point away from centerline = 145μg/m 3

This Lecture and the Next Lecture  This Lecture:  Chapter 6 Page 119~143 Page 149~154  The Next Lecture:  Chapter 7 Page 160~203

Homework Page 152, 6.2 Page 153, 6.3 Page 153, 6.6 Page 134, Example 6.4 What is the SO 2 ground-level concentration at the downwind distance 1km? (H=50m)

DISCUSSIONS Topics about Air pollution:  Introducing yourself  Interesting news or information about air pollution your having read or heard  Your opinions on this Air Pollution course  Your suggestions for Chinese Air Pollution  Other familiar issues about Air Pollution