The secondary precursors of photochemical smog are

Options

A. `SO_(2) and NO_(2)`
B. `NO_(2)` and hydrocarbons
C. `O_(3)` and PAN
D. `CO_(2) and O_(2)`

Explanation

To solve the question regarding the secondary precursors of photochemical smog, we can follow these steps:

### Step 1: Understand Photochemical Smog
Photochemical smog is a type of air pollution that is formed when sunlight reacts with pollutants in the atmosphere. It typically occurs in urban areas with high levels of vehicle emissions and sunlight.

**Hint:** Remember that photochemical smog is closely associated with sunlight and certain pollutants.

### Step 2: Identify Primary Precursors
The primary precursors of photochemical smog are compounds that are essential for its formation. In this case, hydrocarbons (such as those emitted from vehicles) are the main primary precursors.

**Hint:** Think about what types of emissions are prevalent in urban areas and how they contribute to smog.

### Step 3: Define Secondary Precursors
Secondary precursors are compounds that are formed as a result of reactions involving primary precursors and other pollutants. They may not be essential for the formation of photochemical smog but play a significant role in its development.

**Hint:** Secondary precursors are products of chemical reactions that occur after the initial pollutants have been introduced.

### Step 4: Identify Secondary Precursors
The secondary precursors of photochemical smog include:
- Peroxyacetyl nitrate (PAN), which is formed from the reaction of hydrocarbons and nitrogen oxides.
- Ozone, which is formed from the reaction of sunlight with pollutants like nitrogen oxides and volatile organic compounds.

**Hint:** Look for compounds that are generated from the reactions of primary pollutants under the influence of sunlight.

### Step 5: Conclude the Answer
Based on the information gathered, the secondary precursors of photochemical smog are primarily peroxyacetyl nitrate (PAN) and ozone.

**Hint:** Remember that secondary precursors are often products of the reactions of primary precursors and other pollutants.

### Final Answer
The secondary precursors of photochemical smog are peroxyacetyl nitrate (PAN) and ozone.