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Lecture 9

lecture 9 - Aerosals.docx

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Jon Abott

Feb 7 1. Recap a. Ozone in the stratosphere and ozone in trophopshere i. Ozone is a GHG ii. Stratosphere – ozone cools the planet iii. Trophosphere – increases the temperature iv. Generating ozone through NOx and hydrocarbons 2. Aerosoal Effects a. Aerosol is suspension of particles in air. b. Aerosol refers to air+paticles c. For particles to be suspended they can’t fall out d. For them to be suspended, 2 i. Settling velocity = D (terminal velocity when the particle falling down a fluid by gravity) – stolks law ii. Settling velocity scales as the diameter square of the particle e. 1000 microns = 1 mm -1 f. Settling velocity  100 ms g. To go one km in the atmosphere  takes 10seconds h. That is the size of a small raindrop. It is not fair to call a raindrop an aerosol , so we try a much smaller diameter. i. So if it is 100 microns, i. 1oo microns = 0.1 mm 1m/s 1000s 20/15 minutes ; this doesn’t last very long in the atmosphere. ii. 10 microns = 0.01mm 1cm/s 10^5 s  many hours. This could be the starting velocity of an aerosol. Any particle smaller than this would be that. j. If the winds keep moving the air around, they will be mixed aroud =, drifted, k. This is not a good way of removing the prticles, specially if it is small ones. For big ones it is a god way. l. Particles which are 10 microns will get settled down by gravitation. But particles which are smaller than that will not be settled down. 3. You take molecules that are highly volatile that might be generated in the atmosphere and condense them together a. When a volcanoes blows up SO2 Is released i. SO2 +OH (oxidized)  HS03 (g) ; this could be released from coal power plant. Lots of acid rains comes from a dirty coal that has S in it. When you burn the coal S gets oxidized, and it gets released through a power plant ii. HSo3 +o2  HO2 + So3 iii. SO3 +H20  H2So4 - highly involatile, wll condense with anything. b. H2So4 +NH3  breakdown from Uria. c. You can take a couple of molecules from NH3 and H2So4 and you get a cluster. It’s the smallest particles to exist, in nanometers. d. They are formed by Gas - to - particle conversion . So this can be 1 nm. e. There are particles that are few microns in size. They are generally formed through a mechanical process. it could be a truck driving in a dusty road, or high wind velocity. f. There could be dust generated from high wind velocity from dusty deserts, and if you sampled air of the west coast of BC you can see dust coming out of the gobi desert area going to the pacific ocean. These particles could be very few nm in size. g. There is mechanically formed particles, and from gases condensation together to dust formation. h. This is what gives rise to the overall sixe distribution to the particles int eh atmosphere. i. Large ones are mechanically generated – wind blown, volcanoe, sea spray. (when waves break, the falling water traps air bubbles in the ocean, when they come to the surface they form particles.), plant particles. The major loss process for them is sedimentation j. The real tiny ones  on the left side (slide, 1 slide) o.oo1 microns. These are small molecules. They are low volatile vapors. When you take a vapor and turn it into a small particle, (homogenous, because you are taking molecules of he same phase, to form a particle) source of these are called primary particles, beause they are essentially being generated in the atmosphere. k. There are really small particles forming the big particles. l. In the atmosphere there is a fair no of time you are having small particles,medium and large particles. m. Small mode/ Nucleation mode: settle down very quickly/ short time n. Coarse mode : o. Accumulation mode: for the climate this is important. medium sized partices. Size is from 100 nm -1000 nm p. they accumulate: mass from condensation or coagulation. i. Condensation: is when you take another low volatile vapor and condense the vapor molecule into another previous particle. ii. Eg: pre-existing particle which condenses with H2So4 and then condenses down. iii. Coagulation: And this occurs when you have a high no of particles. When an engine, there are high no of particles. Little particles. They have a high density. These particles are bumping into each other, and collide. They coagulate, stick to each other, and grow. iv. So this coagulation factors- and condensation factors which accumulate mass and grow into larger accumulation mode and end up being a droplet. v. Any substance in the atmosphere what matters is not just at how they are formed, but also how they are lost. q. Slide 2 4. China, Beijing: standar level of mass of aerosoal in air pollution alert – 30microgram of cubim meters per air. In here it was 700. 5. North coastal Africa, satellite image: the dust coming off the desert is Saharan dust. This dust can go long distances. From Saharan desert you can get dust coming out. 6. Smoky mountains: naturally smoky/hazy. The reason is that much of the hazes are
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