Characterization of atmospheric turbulence Outline of air pollution dispersion

1 characterization of atmospheric turbulence

1.1 pasquill atmospheric stability classes

1.1.1 table 1: pasquill stability classes
1.1.2 table 2: meteorological conditions define pasquill stability classes
1.1.3 data availability


1.2 advanced methods of categorizing atmospheric turbulence

characterization of atmospheric turbulence

effect of turbulence on dispersion – turbulence increases entrainment , mixing of unpolluted air plume , thereby acts reduce concentration of pollutants in plume (i.e., enhances plume dispersion). therefore important categorize amount of atmospheric turbulence present @ given time. type of disperson scale dependent. such that, flows cloud of pollutant smaller largest eddies present, there mixing. there no limit on size on mixing motions in atmosphere , therefore bigger clouds experience larger , stronger mixing motions. , hence, type of dispersion scale dependent.

the pasquill atmospheric stability classes

pasquill atmospheric stability classes – oldest and, great many years, commonly used method of categorizing amount of atmospheric turbulence present method developed pasquill in 1961. categorized atmospheric turbulence 6 stability classes named a, b, c, d, e , f class being unstable or turbulent class, , class f stable or least turbulent class.

table 1 lists 6 classes
table 2 provides meteorological conditions define each class. stability classes demonstrate few key ideas. solar radiation increases atmospheric instability through warming of earth s surface warm air below cooler (and therefore denser) air promoting vertical mixing. clear nights push conditions toward stable ground cools faster establishing more stable conditions , inversions. wind increases vertical mixing, breaking down type of stratification , pushing stability class towards neutral (d).

table 1: pasquill stability classes

table 2: meteorological conditions define pasquill stability classes

incoming solar radiation based on following: strong (> 700 w m), moderate (350-700 w m), slight (< 350 w m)

data availability

historical stability class data – known stability array (star) data, sites within usa can purchased national climatic data center (ncdc).

advanced methods of categorizing atmospheric turbulence

advanced air pollution dispersion models – not categorize atmospheric turbulence using simple meteorological parameters commonly used in defining 6 pasquill classes shown in table 2 above. more advanced models use form of monin-obukhov similarity theory. examples include:

aermod – epa s advanced model, no longer uses pasquill stability classes categorize atmospheric turbulence. instead, uses surface roughness length , monin-obukhov length.
adms 4, – united kingdom s advanced model, uses monin-obukhov length, boundary layer height , windspeed categorize atmospheric turbulence.




^ walton, john (april 1973). scale-dependent diffusion . journal of applied meteorology: 548. 
^ pasquill, f. (1961). estimation of dispersion of windborne material, meteorological magazine, vol 90, no. 1063, pp 33-49.
^ pasquill, f. (february 1961). estimation of dispersion of windborne material . meteorological magazine. 90: 33–49. 
^ seinfeld, john (2006). atmospheric chemistry , physics: air pollution climate change. hoboken, new jersey: john wiley & sons, inc. p. 750. isbn 978-0-471-72018-8. 
^ ncdc website ordering stability array data
^ aermod:description of model formulation
^ adms 4 description of model developers, cambridge environmental research consultants.