This sounds like a bad idea.

According to the linked article this diamond dust is to be injected into the stratosphere. Wouldn't this interfere with aviation? Airplanes also travel inside the stratosphere. Also, wouldn't placing diamond dust in the atmoshphere interfere with the launching of satellites/ rockets? One could argue that there is also sand dust present, but diamond dust consists of way harder particles than sand. As pointed out in the comments: would't the diamond dust also have an impact on surfaces when it comes down (the example mentioned was scratching of car's windshields) to the ground? Is it safe to breathe?