Longman Dictionary of Contemporary English
Wikipedia
The air at or by the sea is traditionally thought to be healthy. This was variously attributed to iodine or ozone but its cleanliness or salt may be more significant.
Salts generally do not dissolve in air, but can be carried by sea spray in the form of particulate matter.
In modern times, the quality of this air is now degraded by pollution from shipping which burns high sulphur fuel in its engines and so generates large quantities of sulphate aerosols.
Usage examples of "sea air".
Breathing in the sea air and salt spray kicked up by the bow behind the conning tower's weather screen, Hersing took every opportunity to leave the close confines of the pressure hull with its smell of dampness, diesel fumes, and sweat.
Indeed, his grandfather had been born here, in a small house very near Ardmore Bay, had lived the first years of his life breathing that moist sea air, had perhaps held his mother's hand as she'd walked to the shops or along the surf.
And then she and Sexton will meet in the bedroom, her husband undressed and waiting for her between the sheets (ironed just that day, because two days in the sea air puts the wrinkles back in), and the notion of a fresh start will have vanished like a song.
I hope you boys didn't get too tired after all that sea air we gave you the other day.
They stood there daintily, their pink noses raised, sniffing the salt sea air.
The smell of burnt flesh wafted off the corpse, fouling the sea air.
Those were open, slid back to let in the mild, silky warmth of the sea air above Capricorn, and strands of her yellow hair floated free in the breeze.
The sea air--I could smell the salt from where we stood--was busy rusting them out.
Just from the brief walk along the deck, her scent was blended with the sea air.