The speaker feels trapped and worn down by their own stagnation. They describe themselves as complacent, stuck in one spot, going nowhere, and the short, blunt lines ("never growing. never progressing.") make that stillness feel heavy. The walls they built for protection are crumbling, and the simile "like they were never there in the first place" suggests those defenses were weaker than they believed. Trying to gather the pieces of their life is "no use."
The ending shifts the poem's focus. The things the speaker once knew "went up in a cloud of smoke," which then pollutes the earth, tying back to the title, "my pollution." The last line, "my grey cloud is now yours," suggests that private despair doesn't stay private. It spreads to others, perhaps as guilt, or as a quiet confession. The mood is bleak and tired, with a small, uneasy honesty at the close.