**Core Concept**
High-altitude pulmonary edema (HAPE) is a life-threatening condition that occurs in individuals who ascend to high altitudes without adequate acclimatization. It is characterized by non-cardiogenic pulmonary edema, which means that the fluid accumulation in the lungs is not due to heart failure or fluid overload.

**Why the Correct Answer is Right**
HAPE occurs due to the inability of the pulmonary capillaries to adapt to the lower oxygen levels at high altitudes. The hypoxia leads to vasoconstriction of the pulmonary arteries, which increases the pressure in the pulmonary capillaries. This increase in pressure causes fluid to leak out of the capillaries and into the alveoli, resulting in pulmonary edema. The condition is often associated with a characteristic "bilateral perihilar infiltrates" on chest X-ray.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HAPE is not primarily caused by increased left atrial pressure.
**Option B:** This option is incorrect because HAPE is not a condition caused by fluid overload or cardiac failure.
**Option C:** This option is incorrect because HAPE is not a condition caused by air pollution or other environmental factors.

**Clinical Pearl / High-Yield Fact**
HAPE is often associated with a characteristic "bilateral perihilar infiltrates" on chest X-ray, which is a key diagnostic feature. It is essential to recognize HAPE early and treat it promptly with descent to a lower altitude and the use of pulmonary vasodilators.

**Correct Answer: D.**