Balloons

Air Balloons are objects that fly above the trainers in order to deliver features such as Team GO Rocket battles and promotional rewards remotely.

Team GO Rocket Balloons
Since July, 2020, Team GO Rocket members occasionally appear in hot air balloons. These balloons spawn above the Trainer in the Map View and are specific to each Trainer; other Trainers cannot see or interact with another Trainer's balloon. The Trainer can tap on the balloon to encounter the Team GO Rocket member riding in it, which will depend on the situation:
 * If the Trainer had a Super Rocket Radar equipped, Giovanni will be riding in the balloon.
 * If the Trainer had a standard Rocket Radar equipped and did not have a Super Rocket Radar equipped at the same time, a random Team GO Rocket Leader will be riding in the balloon.
 * If the Trainer did not have any Rocket Radar equipped, a Team GO Rocket Grunt will be riding in the balloon.
 * There is a rare chance that the balloon will be a special Meowth balloon carrying Jessie and James and it can show up regardless of equipped Rocket Radar.

Outside of special events, one balloon spawns in a six-hour time period (00:00 to 5:59, 06:00 to 11:59, 12:00 to 17:59, and 18:00 to 23:59), always spawning immediately when the game is opened if it has not in the same period, thus each Trainer can encounter four balloons per day. The balloon will follow the Trainer if they move, but they only stick around for 20 minutes and then fly away.

Unlike PokéStop encounters, equipping or unequipping a Radar after the balloon appears does not change who is in it. In addition, Team GO Rocket balloons with Leaders (including Giovanni) will leave if the Trainer exits the Shadow Pokémon encounter, consuming the Radar while making it impossible to catch the Shadow Pokémon.

Meowth Balloons
The Meowth Balloon is a special type of Team GO Rocket Balloon that features a duel battle between Jessie and James. The balloon appears to have a green basket and a balloon in the shape of a Meowth. The balloon is a homage to the balloon used by Jessie and James in the Pokémon anime. This balloon only appears during special events featuring Jessie and James.

Promotion/Sponsored Balloons
Promotional/Sponsored Balloons are a small white balloons that sometimes appear in Pokémon GO. These balloons, when clicked on, will present a postcard of the company being advertised. Below this postcard will be a button that gives the Trainer the option to the gift, and if they accept, then it will take them to a screen further detailing the advertisement. In addition, it will reward the trainer with items, including Stardust, Revives, and various Berries.

Trivia

 * Niantic teased the release of the Team GO Balloon feature in July by flying real-life promotional balloons in certain locations.