400 parts per million.......Take a gallon of water, and divide into a million parts....On drop into the bucket would be many times more than CO2 in the atmosphere. This bogus climate/global warming ripoff is just that, a scientific ripoff done by liberals to make money, to get control.
It is pretty simple, we, as humans, every time we take a breath and exhale, exude CO2. Plants use this, through the process of photosynthesis, to produce oxygen. It is not an accident, the Earth was designed this way. One entity feeds another.
No one would advocate polluting the environment wantonly. But, really, we are discussing PARTS PER MILLION!
Nobody talks about nitrogen, do they? Well, that is 70% of the Earths atmosphere. Plants, with the exception of a few strains, do not use this for growth. The balance of gasses in the atmosphere changes very little, almost immeasurable, from year to year.
Air quality is influenced more by local and geographic/topographic factors. So, the air in LA may not be as good as the air in San Francisco. Different surrounding mountains and wind create either a stagnant air flow, or a dynamic airstream.
If you want an unbiased, coherent look at the atmosphere, I suggest going to
http://www.drroyspencer.com/
He knows what he is talking about.