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lec9-10-09-air-poll-sm

# lec9-10-09-air-poll-sm - Lecture 9-10 HAS222d-09...

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Unformatted text preview: Lecture 9-10 HAS222d-09 Introduction to energy & environment Air pollution applying flux and concentration ideas to pollution and to basic atmosphere/ocean dynamics • The chapter in Spherical Cow on ‘steady state box models’ assumes simple, well-mixed reservoir with volume M with steady flow F in and out, giving a residence time M/F for water or whatever the flowing material is. One can work in terms of volume or mass, using the density ρ (kg/m 3 ) to convert from one to the other. Then if a pollutant is poured in upstream with a known rate (kg per second) the ultimate steady-state concentration of the pollutant in the reservoir can be calculated. – This model needs much improvement however: • the flow or the pollutant injection may vary with time • the reservoir may not be ‘well-mixed’ (as in smoke in the atmosphere) • indeed the reservoir may not even be well-defined (as in the stratified global atmosphere ,where the pollutant never fills the whole region • the flux of pollutant or other trace substance (e.g.water vapor) is expressed as a concentration C times a flux of mass of fluid: mass flux = ρ VA (kg/m 3 )(m/sec)(m 2 ) …= kg/sec where A is the cross-sectional area of the flow and V the velocity. flux of pollutant or tracer = C ρ VA where C is given as kg of tracer per kg of solution (water + tracer). STIRRING AND MIXING: often a trace substance or pollutant is distributed complexly in a fluid. How does it become diluted in concentration? Think of a red-colored pollutant. Since chemical reactions and molecular diffusion and heat flow occur where surfaces touch, the area of contact between the red fluid and clear fluid is crucial. This is how we mix cake mixes…stirring and stirring until we have stretched out the ‘red’ part enough for chemical reaction to occur along the edges of the red component. In the same fashion, chaotic fluid flow stirs a pollutant (a ‘tracer’),stretching it out until if finally ‘mixes’ by molecular diffusion. Tendrils of bright red lengthen; their surface area increases; finally all is uniformly pink. The figures show a dye tracer being stirred in a fluid…while it is still a chaos of thin red curves before it has mixed to ‘pink’. The biosphere as seen with satellite images of color (here ‘false color’ recoded to bring out detail). Chlorophyll of primary production of vegetable matter (‘grass of the seas’) in ocean; snow-cover, forests, deserts on land and ‘blue deserts’ in ocean. note the bands of wet and dry land..from rain forests to deserts, which are tied to the cycling of fresh water evaporated from the oceans phytoplankton at the surface of the Mediterranean Sea (false color SeaWiFS satellite image) showing complex tendrils due to stirring by ocean currents. Biological communities have to adapt to this chaotic stirred environment: a complex place to raise a family! water vapor in the middle levels of the troposphere, showing very long streaky features extended by storm-like cyclonic weather systems . MORTALITY:...
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lec9-10-09-air-poll-sm - Lecture 9-10 HAS222d-09...

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