7.2: Photochemical Smog

Question 1

Ozone Formation Equation

Answer 1

NOx+VOCs+heat+sunlight

Question 2

PANS (peroxyacyl nitrates)

Answer 2

They are secondary pollutants that can be found in photochemical smog and are resp, eye irritants

Question 3

Photochemical smog precursors

Answer 3

• NO2 is broken by sunlight into NO + O
• VOCs bind with that NO to form photochemical oxidants (carbon-based compounds that evaporate easily)
• Ozone forms when that free oxygen from NO2 breakdown binds to free O2 in the atm

Question 4

Normal O3 formation

Answer 4

• Sunlight breaks NO2 into NO+O
• This free oxygen atom bonds with O2 in the atm. to form ozone
• At night, O3 reacts again with NO to form NO2 and O2 with the O3 levels dropping overnight

Question 5

Photochemical Smog Formation

Answer 5

• Sunlight breaks NO2 into NO + O
• The free oxygen atom bonds with O2 in the atm. to form O3
• VOCs in the atm. bond with the NO to form photochemical oxidants
• Without that NO to bond to, O3 builds up instead of reacting with the NO at night to return to NO2 + O2
• The built up O3 reacts with the photochemical oxidants to produce photochemical smog

Question 6

Factors that increase smog formation

Answer 6

• More sunlight equals more tropospheric ozone, Warmer temps speed up the volatilization of VOCs and the reactions that lead to ozone
• Higher VOC emissions lead to more ozone
• Increased vehicle traffic produces more NO2 which leads to O3 formation

Question 7

Why do urban areas have more smog?

Answer 7

• More traffic leads to more NO2
• Hotter temps due to low albedo from concrete and asphalt
• More VOCs due to gas stations and factories
• More electricity demand leads to more NOx production from power plants

Question 8

Env. impacts of smog

Answer 8

• Less sunlight, less photosynthesis
• Ozone damanges plant stomata and irritates animal resp. tracts

Question 9

Human impacts of Smog

Answer 9

• Resp. irritant and possible resp disease, eye irritation

Question 10

Econ. impacts of Smog

Answer 10

• Increased health care costs to treat resp. irritation
• Lost productivity due to sick workers missing work or dying
• Decreased agricultural yields due to less sunlight reaching crops and damage to plant stomata

Question 11

Reduction

Answer 11

• Vehicles: Less NO2 emissions, less gas and fewer VOCs. More public transport and carpooling, biking, remote work
• Energy: Increased energy prdouction from soruces that don’t emit NOx and natural gas power plants release less NOx than coal