The ozone layer is far enough from organisms not to harm them, but also is close enough to the Earth's surface to maintain the proper temperature and hold its layer rigidity. The stratosphere is the correct answer.

The ozone layer is located in the stratosphere, which is one layer above the troposphere (i.e. where we live).

Fluorine, chlorine, bromine, and iodine are all halogens. Neon on the other hand is an inert noble gas.

Cataracts, skin cancer, and high-intensity sunburns are all on the rise in these countries due to ozone depletion and therefore higher exposure to harmful UV rays.

The Montreal Protocol is an international treaty to phase out production of chemicals that deplete the ozone layer, including CFCs and halocarbons.

Chemical fertilizers are produced to fix nitrogen for farmers' fields, and while fields naturally lose nitrogen to the atmosphere in the form of , increased abundance of fixed nitrogen results in more  being released. Feedlots produce large quantities of nitrogen-rich animal waste, which also decays and enters the atmosphere in massive quantities.

Water vapor is the most abundant greenhouse gas in the Earth's atmosphere. Infrared radiation that gets absorbed and reflected by the Earth's surface gets trapped and reflected back to the Earth's surface by greenhouse gasses in the atmosphere in a process known as the "greenhouse effect."

The only gas in these selections that is made only by man is _, which is a CFC or Chlorofluorocarbon. , methane, can be produced by many other organisms; a key example of this are cows. , or water vapor, has many natural origins such as bodies of water, and finally  also has natural sources like volcanoes.

The variance of annual  levels can be accounted for by a combination of both the  tilt of the Earth on its axis by as well as the revolution of the Earth around the sun. These two factors in conjunction with one another create the seasons. Since the Northern Hemisphere has vastly more plant coverage compared to the Southern Hemisphere, the Earth can uptake more carbon dioxide during the summer and spring seasons due to high levels of photosynthesis; however, when the Northern Hemisphere is in fall and winter, many of its plants cannot photosynthesize, leading to a spike in atmospheric carbon dioxide.

The Northern hemisphere has a much larger basal area comparatively to that of the Southern hemisphere. When the Northern hemisphere is in winter, many of its plants are not able to photosynthesize, therefore the global  levels rise due to much fewer plants actively uptaking that  for their photosynthetic processes. By the same token, when the Northern hemisphere is experiencing spring and summer, the carbon dioxide levels fall due to higher photosynthetic activity.