Residual smoke hazards are most likely during night and early morning in low-lying areas with fog.

Residual smoke hazards are most likely during night and early morning in low-lying areas with fog.

• A. During the middle of the day
• B. At night and early morning
• C. Only during afternoon
• D. Only during windy days

Answer: (B)

The main idea is that smoke tends to linger when the air is very stable and not mixing. At night and in the early morning, especially in low-lying areas, the atmosphere often forms a temperature inversion: cooler air settles near the ground while a warmer layer sits above, trapping air and anything in it, including smoke. Fog also tends to form under these calm, moist conditions, further reducing dispersion and keeping smoke near the surface. Because mixing heights are low and winds are usually light, smoke from a burn doesn’t rise and disperse as it does during the day, so residual hazards remain near ground level and can accumulate in basins or depressions. During the middle of the day, solar heating destabilizes the atmosphere, increasing mixing and raising the plume, so smoke disperses more readily and residual hazards are less likely. Windy days can disperse smoke more quickly, though they may spread particles differently; the key factor for residual hazards is the stagnant, inversive, foggy conditions that trap smoke, which are most common at night and in the early morning in low-lying areas.

The main idea is that smoke tends to linger when the air is very stable and not mixing. At night and in the early morning, especially in low-lying areas, the atmosphere often forms a temperature inversion: cooler air settles near the ground while a warmer layer sits above, trapping air and anything in it, including smoke. Fog also tends to form under these calm, moist conditions, further reducing dispersion and keeping smoke near the surface. Because mixing heights are low and winds are usually light, smoke from a burn doesn’t rise and disperse as it does during the day, so residual hazards remain near ground level and can accumulate in basins or depressions.

During the middle of the day, solar heating destabilizes the atmosphere, increasing mixing and raising the plume, so smoke disperses more readily and residual hazards are less likely. Windy days can disperse smoke more quickly, though they may spread particles differently; the key factor for residual hazards is the stagnant, inversive, foggy conditions that trap smoke, which are most common at night and in the early morning in low-lying areas.