Mystery Poem, By:Mallory

I make your air feel more fresh,
and I have a different personality in each season.

I'm not always the usual green,
I'm not always the bland red.

Sometimes I'm yellow and orange,
Sometimes I'm even brown and crunchy.

I'm not normaly around in the winter,
I'm most definitely around in the summer.

I'm all different shapes, sizes, and styles,
But don't underestimate me, because I can make a big pile!

What am I?