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Environmental Chemistry

Environmental Chemistry

Environmental Chemistry Questions

Bring on the tough stuff

1. How can a volcanic eruption affect global temperatures?

A violent eruption spews sulfate aerosols into the stratosphere, where they remain for years. These aerosols are light colored and so reflect light, decreasing temperatures in the troposphere. In the stratosphere, however, volcanic aerosols absorb solar radiation that is reflected from earth's surface and increase temperatures. Volcanic eruptions can also add to the Junge layer, which acts like a molecular screen controlling the amount of solar radiation reflected and absorbed.

2. A climate scientist experimenting with seeding of cirrus clouds in the tropics accidentally adds too much bismuth (III) iodide. Describe some of the effects this could have on ozone concentrations and weather.

By adding too much bismuth (III) iodide to the cloud, the scientist thickened the cloud and increased the amount of long-wave radiation it would absorb. This would result in warming. The effect of this thickening on ozone concentrations is a little more difficult to ascertain. We know that cirrus clouds act as a meeting spot for the chemical reactions that produce active chlorine. We also know that active chlorine destroys ozone. Putting two and two together, we can deduce that by creating a bigger space for the reactions to occur will result in a decrease in ozone concentration.

3. When it was discovered that CFCs were causing a hole in the ozone layer, they were quickly banned and replaced with HFCs and other compounds. Do you think this was a wise decision? Explain.

There's not really a correct response to this question, as long as you back up your response with solid reasoning. We'll give you our take on CFCs vs. HFCs, but if your take differs, that's probably okay.

CFCs were destroying the ozone layer, so clearly they needed to be replaced. Unfortunately, the HFCs that replaced them are potent greenhouse gases with long atmospheric lifetimes and high GWPs. On the one hand, the banning of CFCs was a giant step toward fixing the anthropogenic input to the hole in the ozone layer. On the other hand, now we have these new compounds floating around for the next 300 years. Overall, we'd give this substitution a toes-down.

4. Residents in Greenville, North Carolina decide to compete in HGTV's "Greenest City" competition. Unfortunately, they take the title of the competition literally and add tons (literally) of fertilizer to "green" their lawns. How could this drastic increase in fertilizer use affect precipitation in the area?

NH3 emitted from fertilizers is somewhat like the OH radical in that scrubs the atmosphere. In NH3's case, it scavenges H+ ions, forming NH4+. In areas with great NH3 emissions, the pH of the rain is generally higher because the NH3 neutralizes approximately 22% of the acidity of precipitation.

5. If methane concentrations in the atmosphere increased by 10%, how could this affect the atmospheric concentration of carbon monoxide? What effect would this have on radiative forcing due to the greenhouse effect?

An increase in methane of 1% = a decrease for OH of 0.32%. So, a 10% decrease in methane would mean a 3.2% increase in OH. The question asks about CO concentrations. An increase in OH is likely to mean a decrease in CO since OH removes CO by reacting with it. Additionally, CO is produced from the oxidation of the formaldehyde formed by reactions between methane and OH. Less methane = less carbon monoxide. Again, we are not taking all reactions in the atmosphere into account here, just the reactions we have gone over in this chapter.

6. If you could skip any sub-section of this chapter, which would you skip? Explain your answer.

Obviously, there are a zillion + 1 possible answers this question. As long as you back up your answer, and it's not something along the lines of "purple elephants dance in my backyard at night" you probably will get credit. In case you were wondering, the section we would love to skip is… none of them.

7. For science class, Mo has to prepare a group presentation on smog. Her portion of the presentation must include measures to reduce smog. She decides that smog could be greatly reduced if all gas-powered school buses were replaced by electric school buses. Is this an effective measure for reducing smog? What are some other measures she should suggest?

Smog is formed by reactions between ozone, VOCs, and hydrocarbons. One of the main reactants in the formation of smog is NO, which is emitted by gas-powered vehicles. Replacing gas-powered vehicles would probably reduce the emissions of smog-forming compounds. Of course, the electric vehicles replacing these gas-powered ones are probably charged with electricity generated through the burning of fossil fuels, and the burning of fossil fuels releases smog-causing chemicals. To really tackle the issue, you'd have to power those electric vehicles up with electricity from solar, wind, or hydropower. Other strategies that could be implemented include tighter regulations on VOCs, the use of low VOC paints in all new construction projects, and better public transportation.

8. Jimmy Jim Junior states that CFCs are making the Earth warmer. Sammy Sam Senior disagrees and says that CFCs caused the hole in the ozone layer. Who is right?

Both are right. CFCs are largely responsible for that gaping, but shrinking, hole in the ozone layer because active chlorine (formed largely through reactions on the surface of cirrus clouds) attacks ozone like a lion on an antelope. CFCs also are pretty potent greenhouse gases with atmospheric lifetimes of up to thousands of years and GWPs in the thousands.

9. Dr. Evil installs a gas shield that blocks all solar radiation less than 240 nm. How could this affect ozone?

Solar radiation less than 240 nm is responsible for the production of ozone. No 240 nm radiation, no ozone. The question doesn't ask about this, but this wavelength of radiation is also responsible for the removal of N2O, PFCs, SF6, and CFCs from the atmosphere. Of course, this wavelength of radiation is also responsible for ozone destruction, but let's not make this overly-complicated because that's like asking the whole chicken and the egg question.

10. Britt, who has been watching too many cartoons starring brainiac scientist children, decides to prove that her brother's fancy bottled water is actually from the taps of beautiful Newark, NJ and not the tropical island shown on the bottle. How can she prove her brother's water is not really all that fancy?

The answer is as simple as isotopic ratios. Water from different locations will have different isotopic signatures. Water from Newark, NJ, for example, will have different isotopes than water from a tropical island. The same process is used to track the origins of everything from cocaine to wine.

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