Peachy sounds right. More vigourous growth, (although its photosynthesis instead of metabolism). Maybe you should ask that "someone" who told you about hardwoods producing over 300 times more O2, where he got his data, or if he is just guessing without scientific measurement or proof. Keep in mind, hardwoods are without any leaves, not producing any oxygen at all for several months, like 8 months, Sept to April inclusive, which is 2/3 of the year, bare, dormant, unproductive. Evergreens are green all year long. Whenever the weather is mild, during mild/warm spells, they're ready and active producing oxygen. In between winter and spring, when weather turns warmer and hardwoods are still deciding to wake up, then slowly starting to bud, evergreens are already doing their job full-time, counteracting our smog, converting our carbondioxide emissions to oxygen.