Chapter 4 - 5

05 Environmental Science

W: OK, so everybody talks about all the pollution that goes into the air, but doesn’t nature have way to take it out?

Actually−and this might surprise some of you—the answer is yes. There are actually four different ways that nature takes particles of various . . . uh, various kinds of pollution out of the air.

So everyone, get out your notebooks and write this down, because it will be in a pop quiz sometime in the near future.

The first way that nature takes bits and pieces of stuff out of the air is through good old—fashioned rain.

Bet you didn’t know that, did you? It’s called rain out. Does anyone have a guess as to how rain helps lessen pollution?

M: Is it because the moisture of . . . um, well, it kind of traps the pollution as it comes down?

W: You’re on the right track, but that’s not it exactly. You see, rain drops start to actually form around the pollution.

Think about it this way. In order for condensation to occur, there has to be something for the moisture to condense on. Well, the pollution in the air is what the rain condenses around.

Then, when it rains, the pollutants fall down to the ground and get absorbed into the soil.

By the way, if you put “rain” on your quiz, you’ll get it wrong. Rain out. Got it?

Let’s move on to… oh, yes, sedimentation. OK.

Say a volcano erupts. It spews huge plumes of ash and soot into the air. It lingers there a few days . . . and then what?

M: It falls to the ground.

W: Exactly! But why? Anyone know? No? OK, well, It’s because of gravity. Basically, many pollution particles are actually heavier than air.

So, if this is the case, they’ll just fall back down to the Earth. It doesn’t get much easier than that, so without further discussion, let’s move from sedimentation to the next, um, the next way that nature sort of cleans itself.

Next up is something with a long name: photodissociation.

It’s not quite as complicated as it sounds, though, so don’t worry. What it is… it’s, um, well, it’s where radiation from the sun breaks down all the chemicals in the air.

It breaks them into other things. I feel like I’m not explaining this well. Basically, the sun’s radiation can break down chemical bonds.

So, if there is an O3 particle, which is ozone, sunlight can break it down into O2: oxygen.

So, as you can see, the sun depletes the amount of ozone in the air.

Finally, we have oxidation. It’s where oxygen combines with other elements to form something else altogether.

M: You mean like with acid rain? I heard something about oxidation having something to do with acid rain.

W: Acid rain is definitely an example of oxidation. The oxygen combines with the sulfuric dioxide in the air, and well, through a lengthy process that I’m not going to get into in this class, well it forms acid rain.

And like rain out, the pollution gets placed back into the soil. And by the way, this last method is a big problem, because when the acid comes down, it kills trees. So the air may be cleaner, but there’s pollution on the ground.

1) Listen again to part of the discussion. Then answer the question.

OK, so everybody talks about all the pollution that goes into the air, but doesn’t nature have way to take it out? Actually−and this might surprise some of you—the answer is yes.

How confident is the professor that nature can eliminate air pollution?

2) What is the professor’s attitude when she says this:

By the way, if you put “rain” on your quiz, you’ll get it wrong. Rain out. Got it?

3) Which natural pollution-reduction method does the professor think is the easiest to understand?