Give three ingredients for photochemical smog.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Photochemical Smog**: Photochemical smog is a type of air pollution that is formed when sunlight reacts with pollutants in the atmosphere. It is commonly associated with urban areas and is particularly prevalent in places like Los Angeles.

2. **Identifying Key Ingredients**: To form photochemical smog, certain ingredients are necessary. These include:
- **Nitrogen Oxides (NOx)**: These are produced from vehicle emissions and industrial processes.
- **Hydrocarbons (HC)**: These are organic compounds that can be emitted from vehicles, industrial activities, and the evaporation of fuels.
- **Ozone (O3)**: This is a secondary pollutant formed when nitrogen oxides and hydrocarbons react in the presence of sunlight.
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