Try the Nature Reserve, which is close to Puerto Madeiro. It's in BA but free of the traffic fumes that afflict the rest of the city. Dogs aren't allowed so no nipping at your heels. Dirt tracks and gravel, ideal for running (in fact you'll see many joggers on the paths).
From the city you have basically 2 areas....(I'm a runner for over 25 years)....You could go down to the ecological reserve (correctly mentioned by bigbadwolf)....wich is down from 9 de Julio....go through Porto Madero and you'll get to that area....just ask once over there. Friends of mine are there doing laps along the boulevard....but you can also go "into" the reserve area. Or you can go to the parks of Palermo....they are a little "cut up" by streets and lights....but there are some loops you can do....there is a mile loop that just about every Argentine and their cousin does, off of Libertador and Sarmiento....straight down from the US embassay....there you can get the full experience of Argentina....and see losts of beautiful Argentine women....If you want race info...let me know