Why do high altitude areas have brighter sunlight and lower temperatures compared to the plains?

(N/A) High altitude areas experience brighter sunlight because the atmosphere is thinner,resulting in less scattering and absorption of solar radiation by dust particles and atmospheric gases.
Additionally,at higher altitudes,the atmospheric pressure is lower. Since temperature is directly related to the density of air molecules,lower atmospheric pressure leads to a decrease in temperature,making these regions colder than the plains.