Tropospheric fallout occurs when the finer particles enter the troposphere, and it spreads over a larger area in the month after the explosion.

• 对流层沈降是在较细粒子进入对流层后，随后在较大面积沈降，一般说来，对流层沈降发生于爆炸后一个月内在爆炸地点的周围地区出现；