How do you remove urine smell from artificial grass?

[#1]

To help eliminate urine smells from artificial grass, you can certainly use Peerless JAL 1L Attack An Odour Indoor. It is very effective for indoor odours and works outdoors as well.

I've spoken the the manufacturer and there are no issues using it outdoors.

It is simply named as an indoor product because the market predominantly uses it for indoor purposes such as hospital environments. 

If you have any concerns about your artificial turf, I recommend doing a small test section in an inconspicuous area to ensure the product does not effect the grass in any way. - MitchellMc

To add to the suggestions made, I recommend using Tuff Turf 500ml Synthetic Grass Deodoriser. 

It is a ready-to-use spray on solution for removing and breaking down urine odours from synthetic grasses.

The completely natural formula attacks the acidic components of pet urine and removes unwanted odours, without providing additional harmful wastes to the environment. - EricL