The "outdoors" smells like a lot of things! I can think of a words referring to various specific scents that recall being out in nature:
earthy, woodsy / woody, mossy, mildewed, moldy, pine, loamy, flowery, fresh. And more of a stretch: crisp, musky, animalic, sweet, heady (like 'the thick smell of nectar')
I mean, there is that something where you breathe "some fresh air" and just feel good, and I find the most evocative descriptions of it have to be phrases, usually by a damn good writer. For your perusal, here is an article devoted to petrichor perfumes with a couple cool descriptions.