Which statement describes a direct climate effect of particulate matter?

• A. PM has no climate effect.
• B. PM only affects climate by responding to humidity.
• C. PM scatters and absorbs solar radiation.
• D. PM increases surface albedo by reflecting all radiation.

Answer: (C)

Direct climate effects from particulate matter come from how aerosols interact with sunlight while they are in the air. PM can scatter solar radiation, sending some of it back toward space, which reduces the energy reaching the surface and tends to cool the planet. It can also absorb sunlight, especially particles like black carbon, which heats the surrounding air and can change atmospheric stability and regional temperatures. This combination—scattering and absorption of solar radiation—is the direct radiative impact PM has on the climate, without involving cloud processes. The other statements miss this key point: PM does have a climate effect; humidity can modify aerosol properties but isn’t the only pathway for a direct effect; and PM does not simply reflect all radiation to increase surface albedo.