A study worked out why urine sprayed onto vertical surfaces by cats to mark their territory is smellier (emits a pungent odour) than urine which is excreted when cats go to the toilet.
They decided that this increased pungent odour of urine designed to mark territory is due to the fact that it has increased adhesion properties and sticks to vertical surfaces more effectively.
The Japanese scientists led by Reiko Uenoyama decided that sprayed urine originates in the bladder like excreted urine and it does not contain added secretions such as anal sac secretions. But they say that it “can effectively emit volatile organic compounds (VOCs) when smeared on vertical objects due to its strong adhesion”.
They also decided that the chemical profiles of volatile organic compounds and odour qualities “were similar between fresh sprayed urine and bladder urine samples immediately after spraying from the same individuals.”
In other words, urine excreted when cats go to the toilet is the same as the urine sprayed onto vertical surfaces to mark territory. The only significant difference it seems to me is that the sprayed urine is more adhesive which allows it to stick to the services for longer which led to “the emission of large amounts of VOCs.”
The increased adhesion properties of sprayed urine is a result, according to the study, of feline-specific proteinuria “arising from excretion of a carboxylesterase that produces a precursor of cat-specific odorants”. This reduces surface tension which increases adhesion to vertical surfaces.
The study title is: Sprayed Urine Emits a Pungent Odor due to its Increased Adhesion to Vertical Objects via Urinary Proteins Rather Than to Changes in its Volatile Chemical Profile in Domestic Cats. The link to the study is: https://doi.org/10.1007/s10886-024-01490-1
