Sometimes , the colour of photochemical smog becomes brown . The reason for this brown appearance is the excess of

Options

A. `NO_2`
B. `SO_2`
C. PAN
D. `CH_4`

Answer

To solve the question regarding the brown appearance of photochemical smog, we can follow these steps:

### Step 1: Understand Photochemical Smog
Photochemical smog is a type of air pollution that occurs when sunlight reacts with pollutants in the atmosphere. It typically contains a mixture of various chemicals, including nitrogen oxides and volatile organic compounds.

**Hint:** Remember that photochemical smog forms under the influence of sunlight and involves chemical reactions.

### Step 2: Identify the Key Pollutants
The main pollutants that contribute to the formation of photochemical smog include nitrogen oxides (NOx), volatile organic compounds (VOCs), and ozone (O3). Among these, nitrogen dioxide (NO2) is significant.

**Hint:** Focus on the pollutants that are known to cause color changes in smog.

### Step 3: Recognize the Color of Nitrogen Dioxide
Nitrogen dioxide (NO2) is a reddish-brown gas. When present in high concentrations, it can impart a brown color to the smog.

**Hint:** Recall the specific colors associated with common air pollutants.

### Step 4: Connect the Dots
When nitrogen-containing hydrocarbons are burned (like in vehicle emissions), they release nitrogen oxides, including NO2. This NO2 contributes to the brown color of the photochemical smog.

**Hint:** Think about the combustion of fuels and the resulting emissions.

### Step 5: Conclusion
The brown appearance of photochemical smog is primarily due to the excess of nitrogen dioxide (NO2) in the atmosphere.

**Final Answer:** The reason for the brown appearance of photochemical smog is the excess of nitrogen dioxide (NO2).

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