Fresh water at the beach?
Newly mown lawn?
Steaks on the grill?
Naw - nothing smells like summer more than the smoke from green mosquito coils, delicately wafting on the evening air.
The smell of freshly turned-over rich, black dirt. That one goes along with the smell of sweat and bugspray and suncreen, too. 
I really dislike those green coils. I have had to leave restaurants because of them. Nasty!
No bug coils around here. The prevailing summer scents are fresh-mown hay and manure.
When I was a kid, I thought those were incense.
The maroon coloured ones smell just the same.