Question

ENSC 102 . Problem Set #6 Due at the beginning of class on Wednesday, May 22 Answer each of the following questions in your own words and using your ow calculations. For worked problens remember to explain any intermediate steps or assumptions, show all units, and box your final anwers. For ful possible credit, make sure your fintished work is legible, prepared on loose-leaf paper, and shows your name and your lab instructorname at the top of the first page 1. Tropospheric composition concepts Explain the following phenomena in your own words a. VOCs do not generally produce O, directly, but they can still contribute to higher O levels in polluted regions. (Include any relevant chemical equations with your explanation.) b. Methane measurements are fairly uniform across most of the Earth's surface, even very far from areas that produce methane, while NO, only shows significant concentrations near actual NO, sources. c. Fine particulate matter can be more hazardous to human health than larger particles 2. Lifetimes and loss rates A particular pollutant has two dominant sinks: deposition (rap 10 days) and chemical oxidation by OH (rOH-20 days) a. What are the rate constants (kdp and kou) for each of these loss mechanisms, in s1? b. What is this pollutant's net lifetime considering both of these losses combined? 3. NO, and Os A city struggling with ozone pollution takes measures to reduce local NO, entissions by 10%. Hoyever, they are surprised (and disappointed) to discover that Os levels do not as a result of this change in fact they go up! Draw a diagram and give a le explanation for why this might have occurred, based on local emissions. What additional regulatory steps might you recommend to safely reduce local pollution? 4. CFC-11 at steady state At peak levels around the time of the Montreal Protocol, global CFC-11 emission rates were estimated at around 350 Gg year l (1 G8" İO g) and mong ratios were nicasured at around 270 ppt (ppt mixing ratio x 1012). Imagine a scenario where emissions were not reduced, but rather held fixed at those rates until CFC-11 achieved equilibrium. a. CFC-11 has a lifetime of around 55 years. What would be its total steady state burden once it reached equilibrium? . NÖ and O A city struggling with ozone pollution takes measures to reduce local NO, emissions by 10%. However, they are surprised (and disappointed) to discover that 03 levels do not decrease as a result of this change -in fact they go up! Draw a diagram and give a plausible explanation for why this might have occurred, based on local emissions. What additional regulatory steps might you recommend to safely reduce local pollution? 4. CFC-11 at steady state At peak levels around the time of the Montreal Protocol, global CFC-11 emission rates were estimated at around 350 Gg year (1 Gg 10 g) and mixing ratios were measured at around 270 ppt (ppt- mixing ratio x 1012) Imagine a scenario where emissions were not reduced, but rather held fixed at those rates until CFC-11 achieved equilibrium. a. CFC-11 has a lifetime of around 55 years. What would be its total steady state burden once it reached equilibrium? b. If CFC-11 is well-mixed in the troposphere, what would have been its final equilibrium mixing ratio under this scenatio, in ppt? CFC-11 has a molar mass of 137.37 g/mol, and there are around 7.8 x 100 molecules in the troposphere Now assume that emissions had been successfully reduced to exactly zero after these peak levels in 1990 a. Given its initial levels and lifetime above, calculate what mixing ratio would be expected 25 years later in 2015, assuming perfect CFC-11 with zero emissions 5. exponential decay. How does this 5. CFC-11 with zero emissions Now assume that emissions had been successfully reduced to exactly zero after these peak levels in 1990. a. Given its initial levels and lifetime above, calculate what mixing ratio would be expected 25 years later in 2015, assuming perfect exponential decay. How does thais calculated value compare to actual CFC-11 measurements shown for 2015 below? , b. what could explain the difference between your simplified calculation and actual Northern Hemisphere Atmospheric CFCs, CO, and SF CFC-12 196020002020 1960 1940

Answer 1

1. a

VOCs means Volatile Organic Compounds i.e. they are Compounds containing Carbon, hydrogen and other elements and are volatile in nature i.e. they can go to the atmosphere in the form of vapors. Examples of VOCs include benzene, butane, formaldehyde, tetrachloroethylene, toluene etc.

VOCs are emitted from different sources like industries, vehicles, home care products and to some extent from the aromatic vegetation also.

VOCs can react with the oxides of nitrogen which are emitted from the combustion of fuel in vehicles, power plants and other combustion sources.

In the presence of sunlight (basically the UV radiation), VOCs, carbon mono-oxide and NOx react to form ozone.

The first step is the breakage of a VOC by a very reactive molecule called the hydroxyl radical.

HCHO + ^•OH → H₂O +

HCH^• radical is unstable and reacts with Oxygen to give a peroxy radical HO₂^•:

2HCH^• + 3O₂ → 2HO₂^• + 2CO₂

The peroxy radical (HO₂^•) will react with NO to produce NO₂.

HO₂^• + NO → + NO₂

NO₂ gets dissociated to Nitric oxide and a single oxygen molecule by the sunlight

NO₂ + UV radiation → NO + O^•

This single oxygen atom reacts with molecular oxygen O₂ to produce ozone

O₂ + O^•   → O₃

Thus ozone is produced with the help of VOCs in the Troposphere.

1 c.

Fine particles are more harmful than larger particles. The main reason is their very small aerodiameter. Particles smaller than 10 micrometers are called pm10. These are heavier and therefore settle down easily in the atmosphere. Also if they get into our respiration system, they are stopped by the mucus in the nose and respiratory tract and therefore are not much harmful

Particles smaller than 2.5 micrometers called pm2.5 are much smaller and therefore very harmful for our health. They are very light and therefore don't easily settle down from the atmosphere, are carried away by air to long distances, and persist in the atmosphere for a very long time.

If they are inhaled by a person, they can not be stopped by our respiratory system and can get into the alveoli of the lungs or from there even to the blood stream also and then to the other organs of the body. That is why they are much more harmful