Tropospheric Photo-oxidation Of Pollutants

Question 1

Smog

Answer 1

Smoke and fog

Question 2

Primary pollutants in photochemical smog event

Answer 2

Hydrocarbons = incomplete combustion of hydrocarbon fuels and emissions of VOCs both natural and man-made
Nitric oxide = by product of high temp combustion of hydrocarbons in air

Question 3

Trigger for formation of photochemical smog

Answer 3

NO slowly oxidised to NO2 = brown gas that absorbs blue light at λ<400 nm giving photodissociation of NO2 to NO and O
O can then form O3 or re-oxidise NO giving a photostationary state

Question 4

Why is ozone in the troposphere an issue

Answer 4

Toxic = strong oxidising agent
Long tropospheric lifetime
Gateway to VOC oxidation which can produce other harmful compounds

Question 5

Primary chain carrier in tropospheric oxidation of VOCs

Answer 5

OH radical

Question 6

What happens to carbonyl products from photoxidation of VOCs

Answer 6

Can undergo further photodissociation

Question 7

Does a smog event end at night

Answer 7

No as when Sun sets the reaction:
NO2 + O3 = NO3 + O2
Becomes very important
NO3 is a strong oxidising agent and can initiate oxidation of VOCs by reaction:
NO3 + RH = R + HNO3
Then allows for sequence of events similar to daytime

Question 8

What is photochemical smog

Answer 8

CO = major component = poisonous
O3, NO2, organic and inorganic nitrates = strong oxidising agents

Question 9

Controlling photochemical smog

Answer 9

Control motor vehicle emissions
Exhaust catalyst which reduces NO to N2, oxidises CO to CO3 and oxidises unturned fuel to CO2 and water

Question 10

Issues with exhaust catalysts

Answer 10

Take 10-15 mins to warm up and are easily poisoned