Few of us might have even bothered to consider air as matter, far more that the apparent nothingness has various components. Fresh air is easy to take for granted, until we go without it at least. When we were first taught that we need air to breathe, we learned soon after the fact that air contained oxygen was responsible for that fact. In later years, we got a bit more detail about the composition of air. Air contains about 21% Oxygen, 78% Nitrogen and less than one percent of trace gases. Later enlightenment showed that this is the composition of dry air. It is important to note that air samples may vary due to the presence of pollutants, natural particles or the nature of the atmosphere in a particular location.
Air is really just gas that is colourless and odourless in its normal state. The components of air can assume the liquid form, but the conditions for that are not present in the earth's atmosphere. The trace gases are an important constituent. They are numerous gases that are critical to climate change processes. This is amazing, considering that trace gases only amount to about 0.93% of dry air. The volume of each element is measured in parts per million by volume or ppmv.
Trace elements include argon, hydrogen, carbon dioxide, neon, helium, methane and krypton and hydrogen. Minor elements would include nitrous oxide, xenon, ozone, nitrogen dioxide and iodine. The sheer number of elements in that 0.93% of dry, filtered air is incredible indeed. The composition of air exists in a delicate equilibrium. The harmful environmental effects of some human activities serve to upset the balance, by introducing more pollutants into the air and increasing the ratio of trace elements (such as carbon dioxide) to harmful proportions.
Dry air is comprised mainly of gases. However, water vapour is present in varying degrees in normal air samples (between 1% and 4%). This would affect climatic conditions such as humidity and precipitation. Dust particles are also present, particularly near the earth's surface. In weather reports, you may hear Sahara Dust being mentioned. This mass of dust particles travels several hundred miles over the Atlantic Ocean with air as its conduit. Some air samples may also contain natural substances like spores, pollen, sea spray and industrial pollutants.
The components of air are subject to the laws of gravity, with the exception of light gases that could escape the earth's atmosphere. The air we are most familiar with is located is the troposphere, close to the earth's surface. Air at different atmospheric levels has varying density, pressure and composition. Beyond the troposphere are the stratosphere, mesosphere and ionosphere. Even at higher altitudes within the troposphere, there are reduced oxygen levels. This isn't even all that can be said about air and its components, but it's a good foundation nevertheless.