What effect does an increase in temperature and a decrease in pressure have on atmospheric density?

• A. Density will increase
• B. Density will decrease
• C. Density will stay the same
• D. Density will fluctuate with humidity

Answer: (B)

Density in the atmosphere follows the idea that it is proportional to pressure divided by temperature (rho = P/(R*T)). When temperature goes up, air expands and becomes less dense; when pressure goes down, there are fewer molecules in each cubic meter, also reducing density. If both changes occur together, they reinforce each other, leading to a lower density overall. Humidity can slightly affect density, since water vapor is lighter than dry air, but the primary result here is a decrease due to the higher temperature and lower pressure. So, density will decrease.