It's got to be the smell of rain on sharp sand, freshly fallen that is.
I still have those memories how as I walk back from school, I could perceive the awe-inspiring smell of raindrops. I used to feel like cupping a handful of the sand and gulping it. Only my sanity stopped me then, and of course, people around.
Even now, I'm always pleased to perceive this smell when it drizzles. It fills me with feelings of gratitude while flooding my mind with memories of my childhood.
I never really given much thought as to what causes the smell but now that you've made me remember, I think I'll do it some research.
There are also seemingly pleasant aromas that turns me off but I wouldn't want to deviate. So, that's it. Thanks for asking!