Absolutely. This is like 20 cars on a circuit! The event itself surely doesn't cause much pollution. In F1 in general, Barcelona and elsewhere, I'd say the circus _surrounding_ it causes by far the most pollution. Logistics to/from the circuit with trucks upon trucks per team, setting up the teams' respective pits, private airplanes to/from the circuit, thousands of spectators to/from circuits, some going by yachts, many by air for at least one stint.

The race track? In the big picture, a rounding error.

I'd guess the regular traffic would just take a detour around the closed roads.

Actually, I'm now also visualizing all the surrounding roads clogged with traffic related to the race. It's not increasing my enthusiasm.

Barcelona has an excellent metro system. The trips will either go via train or not at all. And that’s a good thing.