Yes, that's right, Pluto has an atmosphere. Well, Pluto's atmosphere is not an ocean of air like it is here on Earth, but just a thin shell of gases surrounding a dwarf planet in one part of its orbit around the Sun.
It is important to understand that Pluto's orbit is highly elliptical, bringing the dwarf planet closer and then further away from the Sun at various points in its orbit. At the closest point, a solid nitrogen surface heats up enough to sublimate - go directly from a solid to a gaseous state.
These clouds of nitrogen surround Pluto, but the dwarf planet doesn't have enough gravity to keep them near the surface, so they blast out into space.
In 1988, astronomers discovered that Pluto has an atmosphere by watching it pass in front of a distant star - this is called an astronomical transit. Rather than darkening sharply as the star passes behind Pluto, its light slowly faded behind the atmosphere, so astronomers could measure its thickness and composition.
More accurate measurements were taken in 2002, when astronomers were surprised to find that Pluto's atmosphere was thicker compared to the 1988 measurements when it was first discovered. Astronomers believe this is a seasonal phenomenon. Pluto's surface nitrogen has been exposed to sunlight after a 120-year winter. The nitrogen became gaseous, but it took a while for it to fill the atmosphere.
When Pluto is far from the Sun, its atmosphere disappears (freezes). In the modern time period, it began to disappear by 2015. This is one of the main reasons why NASA sent the New Horizons spacecraft to study Pluto's atmosphere before it disappears for an extended period.