The reason is because the engines produce this material as a waste product. So instead of venting it into space it’s processed and funneled back through the ship to power everything from lights to equipment.
Very efficient and very VERY dangerous. Many Vulcans retired from the VSA because Humans pulled shit like this.
I live north of Tokyo and the temperature here and in many other areas of Japan this summer was the highest ever recorded since recording began in the 1890s.