Okay kiddo, let me explain what the Aarhus Protocol on Persistent Organic Pollutants means.
Do you know what pollutants are? They are things that are bad for the environment and can harm plants, animals and people.
Now, there are some types of pollutants that are called "persistent organic pollutants" or POPs. These are really bad because they don't break down easily and they can stay in the environment for a really long time, even years and years!
But some people got together and decided that they needed to do something about it. So they made something called the Aarhus Protocol.
This is basically a set of rules that countries agreed to follow to try and get rid of these POPs and make sure that they don't harm the environment anymore.
So, countries will work together to reduce and get rid of these pollutants, and they will make sure that they don't travel across borders and harm other countries.
Does that make sense? It's kind of like when you clean up your toys so they don't make a mess and hurt other people. The countries are doing the same thing, just with pollutants instead of toys!