Dust
Lima is a big city of 9 million. With lots of cars and buses, that couldn’t exactly be called low emission. The dark clouds that come out from the exhaust pipes of some of them are like a dark unearthly creature from a fantasy novel.
The coast of Peru is technically in a desert climactic zone. And it doesn’t rain very often. So far we have only had very light rain. All of which means, lots and lots of dust. And it gets everywhere. Amazingly, even vertical surfaces!