Bacon smells good. Like, unreasonably good. There are many reasons for this, say food chemists — 150 to be exact.
As this Reactions/ACS video points out, there are about 150 volatile organic compounds that contribute to bacon's incredible aroma, many of them hydrocarbons and aldehydes, along with some nitrogen-containing compounds. Cooking bacon facilitates the Maillard reaction (a chemical reaction between amino acids and reducing sugars that gives browned foods their desirable flavor). Add to that the melting fats, this reaction produces the complex aroma compounds that smell so irresistibly good.