Carbon dioxide (chemical formula CO2) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature.
In the air, carbon dioxide is transparent to visible light but
absorbs infrared radiation, acting as a greenhouse gas. It is a trace gas in Earth's
atmosphere at 417 ppm (about 0.04%) by volume, having risen
from pre-industrial levels of 280 ppm. Burning fossil fuels is the primary cause of
these increased CO2 concentrations and also the primary cause of global warming and climate change. Carbon
dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. When carbon dioxide dissolves in
water it forms carbonic acid (H2CO3),
which causes ocean acidification as
atmospheric CO2 levels increase.
Carbon dioxide is 53% denser than dry air but is long-lived and thoroughly mixed in the atmosphere. About half of excess
CO2 emissions
to the atmosphere are absorbed by land and ocean carbon sinks. These
sinks can become saturated and are volatile, as decay and wildfires result in the CO2 being released back into the
atmosphere. CO2 is
eventually sequestered (stored
for the long term) in rocks and organic deposits like coal, petroleum, and natural gas.
In Earth’s Atmosphere
Carbon dioxide in Earth's atmosphere is
a trace gas, having a global average
concentration of 415 parts per million by volume (or 630 parts per million by
mass) as of the end of the year 2020. Atmospheric CO2 concentrations
fluctuate slightly with the seasons, falling during the Northern Hemisphere spring
and summer as plants consume the gas and rising during northern autumn and
winter as plants go dormant or die and decay. Concentrations also vary on a
regional basis, most strongly near the ground with
much smaller variations aloft. In urban areas concentrations are generally
higher and indoors they can reach 10 times background levels. CO2 emissions
have also led to the stratosphere contracting by 400 meters since 1980, which
could affect satellite operations, GPS systems, and radio communications.
The concentration of carbon dioxide has risen due to human
activities. The extraction and burning of fossil fuels, using carbon that has been
sequestered for many millions of years in the lithosphere, has caused the atmospheric
concentration of CO2 to increase by about 50% since the beginning of the age of
industrialization up to the year 2020. Most CO2 from
human activities is released from burning coal, petroleum, and natural gas.
Other large anthropogenic sources include cement production, deforestation, and biomass burning. Human
activities emit over 30 billion tons of CO2 (9
billion tons of fossil carbon) per year, while volcanoes emit only between 0.2
and 0.3 billion tons of CO2. Human
activities have caused CO2 to increase above levels
not seen in hundreds of thousands of years. Currently, about half of the carbon
dioxide released from the burning of fossil fuels remains in
the atmosphere and is not absorbed by
vegetation and the oceans.
Increases in atmospheric
concentrations of CO2 and other long-lived greenhouse gases
such as methane, nitrous oxide, and ozone have strengthened their absorption and
emission of infrared radiation, causing the rise in average global temperature
since the mid-20th century. Carbon dioxide is of greatest concern because it
exerts a larger overall warming influence than all of these other gases
combined.
Ozone (/ˈoʊzoʊn/), or trioxygen, is an inorganic molecule with the chemical formula O3. It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O2, breaking down in the lower atmosphere to O2 (dioxygen). Ozone is formed from dioxygen by the action of ultraviolet (UV) light and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the latter, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.
Ozone is a powerful oxidant (far more so
than dioxygen) and has many
industrial and consumer applications related to oxidation. This same high
oxidizing potential, however, causes ozone to damage mucous and respiratory
tissues in animals, and also tissues in plants, above concentrations of
about 0.1 ppm. While this makes ozone a potent respiratory hazard and
pollutant near ground level, a
higher concentration in the ozone layer (from two to eight ppm) is beneficial,
preventing damaging UV light from reaching the Earth's surface.
Ozone as a greenhouse gas
Although ozone was present at ground level before the Industrial Revolution,
peak concentrations are now far higher than the pre-industrial levels, and even
background concentrations well away from sources of pollution are substantially
higher. Ozone acts as a greenhouse gas, absorbing some of the infrared energy emitted by the earth.
Quantifying the greenhouse gas potency of ozone is difficult because it is not
present in uniform concentrations across the globe. However, the most widely
accepted scientific assessments relating to climate change (e.g. the Intergovernmental
Panel on Climate Change Third Assessment Report) suggest
that the radiative forcing of
tropospheric ozone is about 25% that of carbon dioxide.
The annual global warming potential of
tropospheric ozone is between 918 and 1022 tons carbon dioxide equivalent/tons
tropospheric ozone. This means on a per-molecule basis, ozone in the
troposphere has a radiative forcing effect
roughly 1,000 times as strong as carbon dioxide. However, tropospheric ozone is a
short-lived greenhouse gas,
which decays in the atmosphere much more quickly than carbon dioxide. This means that over a 20-year span,
the global warming potential of
tropospheric ozone is much less, roughly 62 to 69 tons carbon dioxide equivalent /
ton tropospheric ozone.
Because of its short-lived nature, tropospheric ozone does not
have strong global effects but has very strong radiative forcing effects on
regional scales. In fact, there are regions of the world where tropospheric
ozone has a radiative forcing up
to 150% of carbon dioxide. For
example, ozone increase in the troposphere is shown to be responsible for ~30%
of upper Southern Ocean interior warming between
1955 and 2000.
Powdered activated carbon can be used to
adsorb and absorb CO2 and Ozone pollution in the atmosphere
Activated carbons are complex products that
are difficult to classify on the basis of their behavior, surface
characteristics, and other fundamental criteria. Activated carbon is
carbon produced from carbonaceous source materials such as bamboo, coconut
husk, willow peat, wood, coir, lignite, coal,
and petroleum pitch.
It can be produced (activated) by Chemical
activation processes: The carbon material is impregnated with certain
chemicals. The chemical is typically an acid,
strong base, or salt (phosphoric acid 25%, potassium hydroxide 5%, sodium hydroxide 5%, calcium chloride 25%, and zinc chloride 25%). The carbon is then
subjected to high temperatures (250–600 °C). It is believed that the
temperature activates the carbon at this stage by forcing the material to open
up and have more microscopic pores. Chemical activation is preferred to
physical activation owing to the lower temperatures, better quality
consistency, and shorter time needed for activating the material.
Normally, activated carbons (R 1) are made in
particulate form as powders or fine granules less than 1.0 mm in size with
an average diameter between 0.15 and 0.25 mm. Thus they present a large
surface-to-volume ratio with a small diffusion distance. Activated carbon (R 1)
is defined as the activated carbon particles retained on a 50-mesh sieve
(0.297 mm). A gram of activated carbon can have a surface area in excess
of 500 m2 (5,400 sq ft),
with 3,000 m2 (32,000 sq ft)
being readily achievable.
James
Dewar, the scientist after whom the Dewar (vacuum
flask) is named, spent much time studying activated
carbon and published a paper regarding its adsorption capacity with regard to
gases. In this paper, he discovered that cooling the carbon to
liquid nitrogen temperatures allowed it to adsorb significant quantities of
numerous air gases, among others, that could then be recollected by simply
allowing the carbon to warm again and that coconut-based carbon was superior
for the effect. He uses oxygen as an example, wherein the activated carbon
would typically adsorb the atmospheric concentration (21%) under standard
conditions, but release over 80% oxygen if the carbon was first cooled to low
temperatures.
In the long-run, powdered activated carbon will change shape to hardened activated carbon, if no action is taken to shake it or mix it into granules powders. Hardened activated carbon means it already reaches the limit to proper functions as adsorbed and absorbed medium. To keep it in the best function as an adsorbed and absorbed of air gases, it must be in powdered activated carbon. Hardened activated carbon can also be a new form of commodity as a fuel in the future.
Airships capable to
carry powdered activated carbon to the atmosphere with environmental benefits
An aerostat is an aircraft that remains aloft
using buoyancy or static lift, as opposed to the aerodyne, which obtains lift by
moving through the air. Airships are a type of aerostat. The term aerostat has
also been used to indicate a tethered or moored balloon as opposed
to a free-floating balloon. Aerostats today are capable of lifting a
payload of 3,000 pounds (1,400 kg) to an altitude of more than 4.5
kilometers (2.8 mi) above sea level. They can also stay in the air
for extended periods of time, particularly when powered by an onboard
generator or if the tether contains electrical conductors. Due to this
capability, aerostats can be used as platforms for telecommunication services.
For instance, Platform Wireless International Corporation announced in 2001
that it would use a tethered 1,250 pounds (570 kg) airborne payload to
deliver cellular phone service to a 140 miles (230 km) region in Brazil. The European Union's ABSOLUTE
project was also reportedly exploring the use of tethered aerostat stations to
provide telecommunications during disaster response.