sMOG

Question 1

What are some gases coming from natural sources?

Answer 1

Carbon monoxide, nitric oxide, and sulfur dioxide, ammonia, hydrogen sulfide, and methane.

Question 2

How are these gases simultaneously removed?

Answer 2

Oxidation by hydroxyl free radicals.

Question 3

How are hydroxyl radicals produced?

Answer 3

When a fraction of O atoms from O3 photochemical decomposition, react with gaseous water.

Question 4

Why are hydroxyls so important?

Answer 4

Without it, most pollutive gases would not be removed from the atmosphere

Question 5

What is smog?

Answer 5

Episodes of air pollution with high levels of ground-level O3

Question 6

What are the original reactants for smog formation?

Answer 6

Nitric oxide and unburned/partially oxidized hydrocarbons.

Question 7

What are the sources of emitting smog-forming pollutants?

Answer 7

Internal combustion engines and electrical power plants respectively.

Question 8

What is the second stage of smog formation?

Answer 8

Formation of VOC reacting in smog.

Question 9

What are Volatile Organic Compounds?

Answer 9

Chemicals that evaporate easily at room temperature, from some solids to liquids

Question 10

Why is sunlight also important in smog formation?

Answer 10

Increase of concentration of free radicals participating in smog formation.

Question 11

What secondary pollutants does sunlight create?

Answer 11

O3, nitric acid, HNO3.

Question 12

What primary pollutants are responsible for smog?

Answer 12

NO and VOCs.

Question 13

What do VOC’s like gaseous hydrocarbons emerge from?

Answer 13

Evaporation of solvents, liquid fuels, and other organic compounds.

Question 14

What are the most reactive VOCs in urban air?

Answer 14

alkenes containing C-C double bond, and aldehydes containing a C-O double bond.

Question 15

How are free radicals formed from VOC like alkenes?

Answer 15

Hydroxyl radical binds to the carbon, abstracting a H from it, leaving a hydride molecule.

Question 16

How is methane an example of radical formaiton?

Answer 16

Loss of a H to hydroxyl, CH3 containing an odd number of electrons.

Question 17

What conditions are required for photochemical smog?

Answer 17

Sufficient vehicular traffic, warmth and sunlight, little movement of air mass so reactants are not diluted or swept away.

Question 18

What is emitted from cars that contribute to smog?

Answer 18

NO from early morning traffic, with gradual oxidation to NO2, with HOO build-up.

Question 20

Why are car emission reductions not a viable solution?

Answer 20

It only removes the excess hydrocarbons, without slowing down nitrogen oxide formation, meaning a lower percentage reduction in ozone and other oxidants.

Question 21

Why is creating policies limiting smog formation difficult?

Answer 21

Challenging to deduce the primary pollutant reactant concentration responsible for smog creation.

Question 22

What is an example of how smog formation is variable?

Answer 22

Computer modelling suggests NO2 reduction more important in eastern US, whilst VOC limits O3 in Mexico City.

Question 23

What is an example of the complicated synergism of smog formation? -

Answer 23

Reducing VOC from 1.2 to 0.8 has no effect on O3 concentration, however reducing Nox level from 0.03 to 0.015, cuts ozone in half.

Question 24

When do NOX limited conditions occur?

Answer 24

High VOC reactants, abundant peroxy free radicals (HOO and ROO), and quick oxidation of NO emissions to NO2.

Question 25

How does NOX limitation result in O3 formation?

Answer 25

Free O atoms following photochemical NO2 decomposition react with O2.

Question 26

Why might reducing NOX concentrations produce more O3?

Answer 26

As more OH is available to react with VOC, as NO2 reacts with radicals to form HNO3.

Question 27

How migh further NOX reductions impact O3 concentration?

Answer 27

When VOC is 0.5ppm, lowering NOX from 0.21ppm by 2/3, increases O3. and further reductions do not increase O3 until 0.5 NOX concentrations.

Question 28

What is real-world consequence of the complicated interactions of NOX and O3?

Answer 28

Less traffic on weekends in Los Angeles increase smog as less NO2 to provide a sink for OH.

Question 29

When might NOX reduce ozone?

Answer 29

When NOX is less abundant, but VOC are plentiful, reducing NOX does reduce O3.

Question 30

How do trees contribute to urban smog?

Answer 30

Deciduous an shrubs emit isoprene, whilst conifers emit pinene and limonene, all hydrocarbons with C=C bonds.

Question 31

Why are blue hazes observed in Great Smoky Mountains and Blue Mountains?

Answer 31

The reaction of VOC in sunlight in absence of NOX, producing carboxylic acids that suspend particles that scatter sunlight.