The ornamental design for an indoor airpurifier, as shown and described.
1. Indoor air purifier
1.1 : Front
1.2 : Right
1.3 : Back
1.4 : Left
1.5 : Top
1.6 : Bottom
1.7 : Perspective (front, top, right)
1.8 : Perspective (back, top, right)
The shadings in the reproductions represent contours only and do not illustrate an ornamentation or decoration on the surface of the product; the parts shown by means of broken lines in the reproductions are not part of the claimed design.