7.2 Photochemical Smog

Precursors (ingredients of smog)

Nitrogen dioxide: broken by sunlight into NO + O (free O + O2 = O3)

Volatile organic compounds (VOX): are hydrocarbons that bind with NO and form and photochemical oxidants

Ozone: forms when NO2 is broken by sunlight and free O binds with O2 to create ozone

Sources of smog

gasoline, formaldehyde, cleaning fluids, oil based paints, and even coniferous trees (pine smell)are released into the atmosphere through various activities like combustion and industrial processes

Ozone is a respiratory irritant in…

the troposphere (at earth’s surface) and is damaging to plant’s stomata which can limit plant growth

Conditions of smog formation

Sunlight drives O3 formation by breaking down NO2 to NO + O before then freeing O atoms that binds with O2

Warmth and hotter temps speeds O3 formation, evap of VOCS thus smog formation

Normal ozone formation

1. Morning commute causes high lvls of NO2 from car exhaust

2. Sunlight breaks down NO2 into NO + O

3. O binds with O2 to form O3

Ozone formation peaks in the day because that is where most traffic is found during morning commute (so more NO2) and where sunlight is most direct

At night ozone reacts with NO to form NO2, which reduces ozone levels and allows for recovery of air quality

Photochemical smog formation

1. Morning commute causes high lvls of NO2

2. Sunlight breaks NO2 into NO + O

3. O binds with O2 to form O3 oxidants

4. VOCs bond with NO to form photochemical smog

5. Without NO ozone continues to buildup instead of returning to O2 and NO2 overnight

6. Then combines with photochemical oxidants (NO + VOCs) to form photochemical smog

Factors which increase smog formation

increased vehicle traffic: increases NO2 emissions therefore O3 formation

Higher VOCs: emissions (gas stations, laundromats, petrochem, and plastic factories

More sunlight (summer afternoon): more ozone

Warmer temperatures: spreads evaporation of VOCs and RXN that lead to ozone

Urban areas have MORE smog due to all these

More traffic more NO2

Hotter temp due to low albedo of blacktop

More VOCS due to gas stations and factories

More electricity demand more NOx from powerplants

Impacts of smog

include respiratory issues, reduced visibility, and environmental damage. Smog can lead to health problems such as asthma and lung infections, and may also harm vegetation and ecosystems

increased healthcare cost due to more asthma/bronchitis to treat

lost productivity due to sick workers missing work or dying

decreased ag. yields due to less sunlight reaching crops and damage to plant stomata

Reduction of smog

decreasing number of vehicles increasing public transportation and promoting cleaner energy sources like renewables