why particulate matters concentration is bigger in the morning and in the evening

The concentration of particulate matter is often higher in the morning and evening due to several factors:

1. Temperature Inversion: During the early morning and late evening, the temperature near the ground can be cooler than the air above it, creating a condition known as a temperature inversion. This can trap particulate matter close to the ground, increasing its concentration.

2. Human Activity: Many human activities that produce particulate matter, such as commuting and cooking, tend to occur in the morning and evening. This can lead to increased concentrations of particulate matter during these times.

3. Atmospheric Conditions: Certain atmospheric conditions, such as calm winds or high humidity, can increase the concentration of particulate matter. These conditions are more likely to occur in the morning and evening.

4. Sunlight: Sunlight can help to break down certain types of particulate matter. Therefore, concentrations can be higher in the morning and evening when there is less sunlight.

5. Emission from Vehicles: During rush hours, which typically occur in the morning and evening, the number of vehicles on the road increases. This leads to more emissions, including particulate matter, contributing to its higher concentration during these times.