List main differences between classical smog and photochemical smog.

Explanation

### Step-by-Step Text Solution

**1. Definition and Formation:**
- **Classical Smog:** This type of smog is primarily formed due to high concentrations of sulfur dioxide (SO2) and particulate matter, which are produced from the combustion of fossil fuels.
- **Photochemical Smog:** This smog is formed through the action of sunlight on nitrogen oxides (NOx) and hydrocarbons (organic compounds) emitted from vehicles and industrial processes.

**2. Nature:**
- **Classical Smog:** It is characterized as reducing in nature, which means it can donate electrons in chemical reactions.
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