Contrails or vapor trails are condensation trails and artificial cirrus clouds made by the exhaust of aircraft engines or wingtip vortices which precipitate a stream of tiny ice crystals in moist, frigid upper air. Being composed of water, the visible white streams are not, in and of themselves, air pollution. However, contrails generated by engine exhaust are inevitably linked with typical fuel combustion pollutants. Contrails might also be considered visual pollution.
Condensation from engine exhaust
A vehicle engine's exhaust increases the amount of moisture in the air, which can push the water content of the air past saturation point. This causes condensation to occur, and the contrail to form. When the fuel is burned, the carbon combines with oxygen to form carbon dioxide; the hydrogen also combines with oxygen to form water, which emerges as in the exhaust. For every gallon of fuel burned, approximately one gallon of water is produced, in addition to the water already present as humidity in the air used to burn the fuel.
At high altitudes this water vapour emerges into a cold environment, (as altitude increases, the atmospheric temperature drops) and the local increase in water vapour density condenses into tiny water droplets and/or desublimates into ice. These millions of tiny water droplets and/or ice crystals form the contrails. The energy drop (and therefore, time and distance) the vapour needs to condense accounts for the contrail forming some way behind the aircraft's engines.The majority of the cloud content comes from water trapped in the surrounding air. At high altitudes, supercooled water vapour requires a trigger to encourage desublimation. The exhaust particles in the aircraft's exhaust act as this trigger, causing the trapped vapor to rapidly turn to ice crystals. Exhaust contrails usually occur at above 26,000 feet. where the temperature is below -40°C (-40°F).
Condensation from wing-tip pressure
The wings of an airplane cause a drop in air pressure in the vicinity of the wing. This brings with it a drop in temperature, which can cause water to condense out of the air and form a contrail but only at higher altitudes. At lower altitudes, this phenomenon is also known as "ectoplasm." Ectoplasm is more commonly seen during high energy manoeuvers like those of a fighter jet, or on jet liners during takeoff and landing, at areas of very low pressure, including over the wings, and often around turbo-fan intakes on takeoff.
Contrails and climate
Contrails, by affecting cloud formation, can act as a radiative forcing. Studies have found that contrails trap outgoing longwave radiation emitted by the Earth and atmosphere (positive radiative forcing) at a greater rate than they reflect incoming solar radiation (negative radiative forcing). Therefore, the overall effect of contrails is a warming. However, the effect varies daily and annually, and overall the size of the forcing is not well known: globally (for 1992 air traffic conditions). Other studies have determined that night flights are most responsible for the warming effect: while accounting for only 25% of daily air traffic, they contribute 60 to 80% of contrail radiative forcing. Similarly, winter flights account for only 22% of annual air traffic, but contribute half of the annual mean radiative forcing.
September 11, 2001 climate impact study
It had been hypothesized that in regions such as the United States with heavy air traffic, contrails affected the weather, reducing solar heating during the day and radiation of heat during the night by increasing the albedo. The suspension of air travel for three days in the United States after September 11, 2001 provided an opportunity to test this hypothesis. Measurements did show that without contrails the local diurnal temperature range (difference of day and night temperatures) was about 1 degree Celsius higher than immediately before; however, it has also been suggested that this was due to unusually clear weather during the period.[
Photo taken by Christian who wrote ...
"I took this photo on December 21, 2004 in Mazatlan, Mexico. I stood on my balcony and asked for a sign from the universe. Immediately, a vertical cloud formed, spiraling up like a vortex, reminding me of DNA. A few days later, on December 26, 2004, an underwater earthquake and tsunami hit Indonesia. Earth changes have come fast and furious ever since."
The Chemtrail Conspiracy Theory
The Chemtrail conspiracy theory holds that some contrails are the result of chemicals or biological agents being deliberately sprayed at high altitude for a purpose undisclosed to the general public. Versions of the conspiracy theory circulating on the internet and on some radio talk shows theorize that this activity is directed by government officials, and federal agencies have received thousands of complaints from people who have demanded an explanation. The existence of chemtrails has been repeatedly denied by federal agencies and scientists.
The term chemtrail does not refer to common forms of aerial spraying (e.g., crop dusting, cloud seeding or aerial firefighting). The term specifically refers to aerial trails allegedly caused by the systematic high-altitude release of chemical substances not found in ordinary contrails, resulting in the appearance of supposedly uncharacteristic sky tracks. Believers of this theory speculate that the purpose of the chemical release may be global dimming or population control, and claim that these trails are causing respiratory illnesses and other health problems.
The chemtrail conspiracy theory began to circulate in 1996 when the United States Air Force (USAF) was accused of releasing unknown substances from aircraft which were creating unusual contrails. The Air Force characterizes the accusations as a hoax fueled in part by authors citing an Air University strategy paper entitled Weather as a Force Multiplier: Owning the Weather in 2025 to allege the Air Force was currently conducting a secret government program to modify the weather. The paper was presented in response to a military directive to anticipate future developments and strategies for maintaining the United States' military dominance in the year 2025 and identified as "fictional representations of future situations/scenarios". The Air Force denies it is actually conducting such experiments or that such experiments are planned, and points to the refutations presented by accredited universities, scientific organizations and major news organizations as further evidence the chemtrails do not exist.
Various versions of chemtrail conspiracy theory have circulated through internet websites and talk radio programs. In some of the accounts, the chemicals are described as barium and aluminum salts, polymer fibers, thorium, or silicon carbide. In other accounts its alleged the skies are being seeded with electrical conductive materials as part of a massive electromagnetic superweapons program based around the High Frequency Active Auroral Research Program (HAARP).
The reasons given by those who believe in the conspiracy vary widely as well between military weapons testing, chemical population control, or measures to mitigate global warming. Federal agencies and scientists have consistently denied these claims, insisting the sky tracks are simple contrails. As the chemtrail conspiracy theory spread, federal officials were flooded with angry calls and letters. A multi-agency response to dispel the rumors was published in a 2000 fact sheet by the Environmental Protection Agency (EPA), the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), a step many chemtrail believers interpeted as further evidence of the existence of a government cover-up.
In 2001, United States Congressman Dennis Kucinich introduced legislation that would have permanently prohibited the basing of weapons in space, and chemtrails were listed as one of a number of exotic weapons that would be banned. The bill received an unfavorable evaluation from the United States Department of Defense and died in committee. No mention of chemtrails appeared in the text of any of the three subsequent failed attempts by Kucinich to enact a Space Preservation Act.
Contrails and Chemtrails
Proponents of the chemtrail theories differentiate chemtrails from contrails by describing them as streams that sometimes persist in the sky for hours, and which sometimes trace criss-crossing, grid-like patterns, or parallel stripes which eventually blend to form large clouds. Another feature that proponents say distinguishes a chemtrail from a contrail is the presence of visible color prisms in the streams, unusual concentrations of sky tracks in a single area, or lingering tracks left by unmarked or military airplanes flying in atypical altitudes or locations.
Government agencies and other experts on contrail or atmospheric phenomena deny the existence of chemtrails, insisting that the characteristics attributed to them are simply features of contrails responding differently in diverse conditions in terms of the sunlight, temperature, horizontal and vertical wind shear, and humidity levels present at the aircraft's altitude.
These experts respond that what appears as patterns such as grids formed by contrails result from increased air traffic traveling through the gridlike United States National Airspace System's north-south and east-west oriented flight lanes, and that it is difficult for observers to judge the differences in altitudes between these contrails from the ground.
The jointly published fact sheet produced by NASA, the EPA, the FAA, and NOAA in 2000 in response to alarms over chemtrails details the science of contrail formation, and outlines both the known and potential impacts contrails have on temperature and climate.The USAF produced a fact sheet as well that described these contrail phenomena as observed and analyzed since at least 1953. It also rebutted chemtrails theories more directly by characterizing the theories as a hoax and denying the existence of any chemtrails.
Patrick Minnis, an atmospheric scientist with NASA's Langley Research Center in Hampton, Virginia, is quoted in USA Today as saying that logic is not exactly a real selling point for most chemtrail proponents. "If you try to pin these people down and refute things, it's, 'Well, you're just part of the conspiracy'", he said.
Proponents reject the explanations that chemtrails are in fact contrails or other, natural, phenomena, and assert that because explicit reference to chemtrails was entered into the congressional record with the first proposed Space Preservation Act submitted in 2001 by Congressman Kucinich, there has been official government acknowledgement of their existence.