I'm really quite taken with these. What is it that makes them so atmospheric?

The viewer has to peer into the pictures to make sense of them. That makes them actively involving.

In all the pictures the subject is far away, and often partially obscured. Sometimes they have their back to the viewer and are moving away, begging to be followed.

And the lovely sketchy drawing style is vague and diffuse, so you have to squint and, again, peer into the picture to try to make it clear. But it never becomes clear.