Below are the keyboard shortcuts when using the Environmental painter in the Scene view:
Tab: switch between Spawning and Masking mode.
Hold Shift: enable follow surface normal spawning.
Hold Ctrl: enable erasing brush.
Plus (+): increase brush size.
Minus (-): decrease brush size.
Shift Plus: increase object scale.
Shift Minus: decrease object scale.
Note: Scene view must have focus to use these shortcuts