https://www.gamespot.com/articles/pokemon-go-giving-rewards-for-earth-day-events/1100-6457937/

Pokemon Go is putting some of its eager trainers to work tidying the planet to celebrate Earth Day. The Pokemon Go Earth Day Clean Up is a series of events to take place on April 22, inviting trainers to meet and take care of their environment and neighborhoods.

Coordinating the event will be handled by Playmob, which is partnering with community organizations. Each event will focus on gathering garbage and debris in public spaces. Those who participate can receive a special avatar item, and a collective prize will be awarded to all trainers if enough of them participate. If 1,500 trainers participate, everyone will get double catch Stardust for Ground, Water, and Grass-type Pokemon for 48 hours. If more than 3,000 participate, it will become triple.