Photochemical smog formation

What happens between 6 AM – 9 AM during photochemical smog formation?

As people drive to work, concentrations of NOx and VOCs increase.

What are the key formulas during 6 AM – 9 AM?

• N₂ + O₂ → 2NO

• NO + VOCs → NO₂

• NO₂ + UV → NO + O

What happens between 9 AM – 11 AM during photochemical smog formation?

As traffic decreases, NOx and VOCs react to form nitrogen dioxide (NO₂).

What is the key formula during 9 AM – 11 AM?

• 2NO + O₂ → 2NO₂

What happens from 11 AM – 4 PM as sunlight increases?

Nitrogen dioxide is broken down by UV light, and ozone (O₃) is formed.

What are the key formulas during 11 AM – 4 PM for ozone formation?

• NO₂ + UV → NO + O

• O₂ + O → O₃

What else happens with nitrogen dioxide from 11 AM – 4 PM?

It reacts with water vapor to form nitric acid and nitric oxide.

What is the formula for nitric acid formation from NO₂?

• 3NO₂ + H₂O → 2HNO₃ + NO

How are toxic PANs (peroxyacetyl nitrates) formed from NO₂?

NO₂ reacts with VOCs to form PANs.

What is the formula for PAN formation?

• NO₂ + VOC → PAN

What happens at 4 PM regarding smog formation?

As the sun sets, photochemical smog production stops.

What is the overall reaction that summarizes photochemical smog formation?

• NO + VOC + O₂ + UV light → O₃ + PAN