If natural PM production is low, what happens to man-made particulates?

If natural PM production is low, what happens to man-made particulates?

• A. Remain the same
• B. Increase
• C. Decrease
• D. Become negligible

Answer: (B)

When ambient PM comes from both natural and human-made sources, the mix depends on how strong the natural sources are. If natural PM production is low, the natural portion shrinks, so the same amount of anthropogenic emissions makes up a larger share of the total PM. In other words, the man-made component becomes more prominent relative to natural PM, so it appears to increase. (Note that the absolute amount of man-made PM still depends on emission rates; the key idea is the relative contribution rises when natural sources are weaker.)

When ambient PM comes from both natural and human-made sources, the mix depends on how strong the natural sources are. If natural PM production is low, the natural portion shrinks, so the same amount of anthropogenic emissions makes up a larger share of the total PM. In other words, the man-made component becomes more prominent relative to natural PM, so it appears to increase. (Note that the absolute amount of man-made PM still depends on emission rates; the key idea is the relative contribution rises when natural sources are weaker.)