Many people believe that early morning is the time when the air is the freshest. In reality, this is entirely the opposite; early morning is actually the time when the air is the least fresh.
Evening Weather: As night falls, the temperature on the ground gradually decreases, reaching its lowest point around midnight. This creates a noticeable temperature difference between the warm air above and the cooler air below. Consequently, a layer of air forms at ground level that is distinct from the air above. This layer acts like a giant bowl turned upside down, trapping dust and pollutants in the air close to the ground, preventing them from dispersing or rising to higher altitudes. Additionally, plants release carbon dioxide at night, which further 
contributes to air pollution. This layer of air can also easily form during dusk. Therefore, the atmosphere around six or seven in the evening is not clean either.
So when during the day is the air the freshest? It is around 10 AM. After the sun rises, the temperature on the ground gradually increases, and the “upside-down bowl” effect diminishes, allowing dust and impurities to disperse into the sky. As a result, the air around 10 AM is the freshest of the day.
