Planespotterx From , joined Dec 1969, posts, RR: Posted (5 years 5 months 2 weeks 5 days 22 hours ago) and read 1846 times:
Correct me if im wrong, but arent contrails from aircraft just vaporised ice crystals from the heat of the engines?
I ask this because everytime I tune into the BBC news, there always saying that aircraft contrails are polluting the atmosphere, I thought it was only 1% of a aircrafts flight was pollutants.
I mean why is everyone getting so worked up about aircraft and the environment impact, why not induce a tax on trains or buses, aircraft arent that polluting are they...
Ive always thought that the fuel in aircraft were burn up before it left the engine, or am i wrong...
Contact_tower From Norway, joined Sep 2001, 536 posts, RR: 1 Reply 1, posted (5 years 5 months 2 weeks 5 days 21 hours ago) and read 1813 times:
There is engine exhaust! Same as one a car! (or kinda )
Because it's introduced to the outside air at altitude, it's effect on the ozon layer is grater.
Vzlet From United States, joined Mar 2004, 776 posts, RR: 0 Reply 2, posted (5 years 5 months 2 weeks 5 days 20 hours ago) and read 1804 times:
As I understand it, it's not the physical content (water) of the contrails that's the problem, but rather that contrails can accumulate to such a degree that they block enough sunlight to, over time, influence local weather patterns.
Jet exhaust does contains pollutants, but these are created whenever an engine is running regardless of whether conditions cause contrail formation or not.
"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
Oly720man From United Kingdom, joined May 2004, 4767 posts, RR: 12 Reply 3, posted (5 years 5 months 2 weeks 5 days 18 hours ago) and read 1782 times:
Exhausts contain CO2, NOx, water vapour and possibly CO and particulates, and, of course, heat.
The contrails are water vapour condensing into droplets/ice. The water is the product of the combustion process, fuel+air --> CO2+water+other stuff.
Aircraft may be thought to pollute more because they burn a lot more fuel. I think I read somwhere that the volume of fuel used by a B747 to taxi to a runway would keep an average car going for a year, or something like that - 25 litres a week -> 1300 litres per year. What does a 747 take? 60000 litres per flight?
I saw a program on tv over here in the UK (Jeremy Clarkson flying round the world in his "Great Inventions" series, for UK viewers) in which it was stated that in the days of no flying in America after 9/11 the days were on average 1 deg C warmer and the nights 1deg C cooler because the shielding effects of the contrails weren't there those few days.
Andy
Man City p3 w3 d0 l0 f4 a0 P9 - hey it may never happen again!
Starlionblue From Greenland, joined Feb 2004, 13594 posts, RR: 68 Reply 7, posted (5 years 5 months 2 weeks 2 days ago) and read 1563 times:
The 747 uses less fuel crossing the pond than if you put the same amount of people in compact cars (two per car) and travelled the same distance. Of course, the 747 is just a tad faster. So I would say it's a pretty green giant.
Contrails (my understanding) are not exhaust, although the exhaust is somewhere in there. What happens when something massively hot (exhaust gases) meets something extremely cold (air at 40000ft)? Vapor in the exhaust condenses into droplets since the lower temperature air cannot retain the moisture. If you look at pictures, contrails don't form for quite some distance behind the plane.
This is also why contrails typically don't form at lower altitudes.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
Bruce From United States, joined May 1999, 4950 posts, RR: 28 Reply 8, posted (4 years 5 months 3 weeks 11 hours ago) and read 1328 times:
Quoting Starlionblue (Reply 7): contrails don't form for quite some distance behind the plane
I have seen some contrails VERY close to the plane and other far away.
Why do contrails not form at 25,000 feet? Surely it is colder at FL370 but is it because the colder air can hold less moisture? But then why on some days a plane even at FL370 will not show a contrail. Quite confusing!
bruce
Bruce Leibowitz - Green Bay, WI (GRB/KGRB) - Canon 20D/100-400L IS lens
Starlionblue From Greenland, joined Feb 2004, 13594 posts, RR: 68 Reply 10, posted (4 years 5 months 3 weeks 10 hours ago) and read 1295 times:
Quoting Bruce (Reply 8): Quoting Starlionblue (Reply 7):
contrails don't form for quite some distance behind the plane
I have seen some contrails VERY close to the plane and other far away.
I will amend my statement. Contrails are much less apparent close to the plane because all the droplets have not had time to condense yet and the exhaust is still cooling.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
Tornado82 From , joined Dec 1969, posts, RR: Reply 11, posted (4 years 5 months 3 weeks 9 hours ago) and read 1294 times:
Quoting Oly720man (Reply 3): in which it was stated that in the days of no flying in America after 9/11 the days were on average 1 deg C warmer and the nights 1deg C cooler because the shielding effects of the contrails weren't there those few days.
Wow *shakes head* Maybe that's because during the time of 9/11 the US was also under a VERY strong (for that time of year) high pressure system... which led to crystal clear skies irregardless of contrails... which led to bright sunny days (warm) and cool dry clear nights (good for radiational cooling). A 3 day sample is nowhere near conclusive enough to be considered scientific. There's research that our +/- 150 years of widespread meteorological observations aren't even enough proof to fully prove the theory of global warming, because in the geologic time scale of this planet 150 years is the equivalent of a second or two if scaled down to your life time... pretty insignificant. So obviously 3 days was definitely not enough to make any consequential results for any reputable scientist.
PS: Since this is A.net where everyone screams "Speculation" and "Show me proof" I hold a B.S. in Meteorology, those are my credentials.
David L From United Kingdom, joined May 1999, 8273 posts, RR: 41 Reply 13, posted (4 years 5 months 3 weeks 8 hours ago) and read 1254 times:
Quoting Espion007 (Reply 4): Because their actually called chemtrails and are mind controlling drugs being sprayed into our atmosphere by our goverment
Oh, how I miss those Chemtrail Central discussions from a couple years ago!
B727-200 From Australia, joined Nov 1999, 1049 posts, RR: 4 Reply 16, posted (4 years 5 months 3 weeks 2 hours ago) and read 1208 times:
Engines 'exhaust' moisture in two ways, firstly by any unburnt fuel that has past through (I do not believe 100% combustion has been achieved yet) and water as part of the reaction between oxygen in the air and hydrocarbons.
Contrails can also be formed in atmospheres more laden with moisture by the pressure zones created by the wing. This is like when you see the condensation over the wings when an aircraft is landing on a rainy day, except at altitude the water droplets freeze making them more visible.
Skywatch From United States, joined Mar 2005, 916 posts, RR: 8 Reply 17, posted (4 years 5 months 3 weeks 1 hour ago) and read 1207 times:
Contrail formation relies on exhaust, humidity, and cold temperature. I get annoyed when the air is so dry that I can only easily spot biz jets at FL430(Because they are the only ones with contrails). On other days, there will be planes flanked with contrails at FL270. Watch closely some time and you will see a plane go through pockets of dry air. The contrail will be trailing behind, then it will stop, then start again..... If strong winds accompany the contrails, then they can get very large as they diffuse into the atmosphere. On most summer days here in central Texas, the lower-level air is moderately humid, with patchy clouds dotting the sky. However, the only contrails are usually past FL390.(Because of the intense cold at these levels)
Jetlagged From United Kingdom, joined Jan 2005, 2028 posts, RR: 14 Reply 20, posted (4 years 5 months 2 weeks 3 days 15 hours ago) and read 950 times:
Quoting Oly720man (Reply 3): I saw a program on tv over here in the UK (Jeremy Clarkson flying round the world in his "Great Inventions" series, for UK viewers) in which it was stated that in the days of no flying in America after 9/11 the days were on average 1 deg C warmer and the nights 1deg C cooler because the shielding effects of the contrails weren't there those few days.
The fact that it was presented by Jeremy Clarkson should give you a clue as to how much you can rely on it.
Opinionated? Yes. Entertaining? Yes. Sensationalist? Yes. Reliable factually? Not very.
Contrails disperse fairly quickly. Their shielding effects are grossly overrated in my humble opinion. Sounds more like the anti air travel lobby having another go.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Glom From United Kingdom, joined Apr 2005, 2250 posts, RR: 11 Reply 21, posted (4 years 5 months 2 weeks 3 days 10 hours ago) and read 922 times:
Quoting Tornado82 (Reply 11): So obviously 3 days was definitely not enough to make any consequential results for any reputable scientist.
A most respectable post.
Quoting Jetlagged (Reply 20): The fact that it was presented by Jeremy Clarkson should give you a clue as to how much you can rely on it.
Opinionated? Yes. Entertaining? Yes. Sensationalist? Yes. Reliable factually? Not very.
Contrails disperse fairly quickly. Their shielding effects are grossly overrated in my humble opinion. Sounds more like the anti air travel lobby having another go.
But he's still a legend.
The mechanism behind the suspected contrail effect is based on radiative transfer. They cause white streaks in the sky that insulate against the sun by day and against cooling by night. Contrails presumably must exist to have the effect on radiative transfer that is attributed to them. On some humid days they do persist, but on most days, they disperse fairly quickly, so they cannot have this effect.
Even the kings of spin, the IPCC, say the level of understanding of aviation related effects (contrails and cirrus) is "very low". Of course in a chaotic and non-linear, there is no denying they are a factor, but we're certainly not in a position to blame them for anything yet.
The anti air travel lobby hated us long before James Hansen came along.
£37 Aberdeen to Birmingham, £38 Birmingham to Watford => trains are rubbish!
Tornado82 From , joined Dec 1969, posts, RR: Reply 22, posted (4 years 5 months 2 weeks 2 days 8 hours ago) and read 814 times:
Quoting Glom (Reply 21):
The mechanism behind the suspected contrail effect is based on radiative transfer. They cause white streaks in the sky that insulate against the sun by day and against cooling by night. Contrails presumably must exist to have the effect on radiative transfer that is attributed to them. On some humid days they do persist, but on most days, they disperse fairly quickly, so they cannot have this effect.
Also, that insulating effect would be at the FL's where the jets are creating the contrails... for an average for the sake of discussion let's say ~FL330. There is alot of atmosphere between the surface and that ~FL330 for that surface heating to radiate up into the sky each and every night, away from the surface, cooling the temperatures we feel. Additionally, most nights there is typically a diurnal inversion set up between the surface and where any contrails would be, which is insulating that heat far better than any contrail-sourced cirrus cloud would.
By theory, the contrails would be doing a better job at blocking the sun, i.e. cooler temps, less UV radiation for skin cancer, etc. than they would be at blocking night-time radiational cooling. So does this mean contrails are good for us?
Remember... nearly everything you see related to meteorology lacks the historical evidence to back any kind of "long term effects" theories. There are no reliable, widespread weather records beyond about 150 years here in the US... even in most East Coast cities established in the 1700s. And even for those that there are going back at least a century here and abroad for our European friends where "history" goes back further... how accurate would any temperature measuring equipment have been way back then??
You need to have very small solid particles as the "seed" for the ice crystal formation, present in the exhaust. The other element is the moisture, which is either already present in the air, or is further added by the exhaust. (If the hydrocarbons in the fuel were completely combusted, water and CO2 would be the only results.)
AirEuropeUK733 From United Kingdom (England), joined Apr 2004, 923 posts, RR: 18 Reply 25, posted (4 years 5 months 1 week 5 days 23 hours ago) and read 646 times:
Quoting Espion007 (Reply 4): Because their actually called chemtrails and are mind controlling drugs being sprayed into our atmosphere by our goverment
LMAO Here we go again! Let's re-ignite the chemtrail/contrail thread!
AE733
Life isn't measured by the number of breaths you take, but by the number of moments that take your breath away.
Sponsor Message: 
From , joined Dec 1969, posts, 
From Norway, joined Sep 2001, 536 posts, 
)
From United States, joined Mar 2004, 776 posts, 
From United Kingdom, joined May 2004, 4767 posts, 
From Denmark, joined Dec 2003, 1691 posts, 
From Greenland, joined Feb 2004, 13594 posts, 
From Germany, joined Jan 2006, 0 posts, 
From Australia, joined Nov 1999, 2287 posts, 
From India, joined Sep 2001, 542 posts, .gif){kind=small}
From United Kingdom (England), joined Apr 2004, 923 posts, 
Here we go again! Let's re-ignite the chemtrail/contrail thread!
Sponsor Message: 
Printer friendly format
