Trees and Oxygen

     Someone posted on Facebook that each day a forty foot tree takes in 50 gallons of dissolved nutrients from the soil, converts that into ten pounds of carbohydrates and releases 60 cubic feet of pure oxygen into the air. 
     I wasn't sure whether to be impressed or not. I mean, I have no idea how much oxygen I need to breathe each day. This might be a massive amount of oxygen in relation to my needs as a human, or it might be rather puny. So I did a little research and found an article by Luis Villazon in the BBC Focus magazine. According to this article, a human breathes about 9.5 tons of air in a year. Oxygen, however, is only 23% of the air we breathe (by mass) and we only take in about 1/3 of the oxygen that is available to us in the air of each breath. That means we need 740 kg of oxygen per year. 
      So, how many trees do I need to support my personal oxygen habit? According to Villazon's article I need 7 or 8 trees. Another article says I only need about two trees to produce my oxygen. But, of course, this depends on various other factors. Redwoods, aspens and oaks tend to produce more oxygen than other types of trees. But, THIS depends on where the tree is in its lifecycle as trees what are still growing produce more oxygen than trees who have reached their mature size. 
      As for the 'how' they produce oxygen, the scientists are in agreement on this: through the process of photosynthesis when trees take sunlight, add carbon dioxide from the air --  this produces oxygen. But it sounds like magic to me!