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Love is in the air is correct.

Air, like ground, sea, etc can have a generic or abstract meaning, e.g. air is necessary for life, there are many kilometres of sea between India and Africa, a farm is an area of cultivated ground, but these words can also be used with the definite article 'the'. The air that we breathe. The air which surrounds us. The sea upon which ships float, and in which fish live. The ground beneath our feet. When a feeling, e.g. fear, love, hope, etc, is said to be 'in the air' that is a figure of speech meaning that the feeling is widely felt and surrounds the speaker and/or listener, so much so that it could be poetically imagined to be floating in the air around them like a smell, or like smoke.