I’m very happy to see your interest in applied chemistry at a young age! The key to “science” is the scientific method. Be sure that your team understands the steps, and make a document to show how you followed them. The attached graphic is a short description of the process. Your team may really be at the “Hypothesis” stage from your question. You need to state WHAT you expect the titanium dioxide to do with the smog. Smog itself is a complex mix of different things in the air. It will be helpful to your project to define a single objective in your hypothesis. For example, you might think that the billboard painted with TiO2 will adsorb particulate matter from the air. How will you test that hypthesis (the experiment)?
Part of the project is to show how you came up with your hypothesis. You don’t want to just repeat someone else’s ideas – although they can be useful guidelines. A search for properties of titanium dioxide might help, or it might indicate that it is not the best material for your intended outcome. So, where did you get the idea? Maybe some of the references in that source can be used to describe how it is supposed to work. Will it attract certain pollutants, and bond with them to remove them? Maybe it forms a structure when applied that is good for trapping small particles. Those questions are part of the research process.
Remember, good questions are needed to design a good experiment that can either support or refute your hypothesis. Either way, GOOD science gives us new information, even if the outcome is not the one we were hoping for at the start. Good Luck, and have fun experimenting!