Thomas Pringle (Donegal South West, Independent)
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218. To ask the Minister for Environment, Community and Local Government if he has carried out any research into the effect of chemtrails or contrails, and their effect on the environment; and if he will make a statement on the matter. [23993/15]

Alan Kelly (Tipperary North, Labour)
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My Department has not carried out any research into what are sometimes called chemtrails, as these are not a scientifically recognised phenomenon.

Neither has my Department carried out any research into the effect of contrails. However, the Environmental Protection Agency (EPA), is currently funding a PhD study on contrails and their potential effect on climate as part of its STRIVE research programme. The study titled Cloud cover and radiation balance changes over Ireland due to aircraft induced contrails is due to be completed later this year.

My Department has previously been informed by Met Éireann that vapour trails are formed through the emission of exhaust gases from jet engines of aircraft in the upper troposphere and that the main component of these gases is water vapour.  Ambient air temperature at jet cruising altitudes is often below -500C. Under these conditions, water vapour cools and condenses and the particles act as ice nuclei, leading to the production of ice crystals; these ice crystals are what are visible from the ground as a linear cloud of condensation.

Depending upon atmospheric conditions, these vapour trails can rapidly dissipate or remain for some time, gradually spreading horizontally into an extensive thin cirrus cloud layer. Water in the atmosphere commonly evaporates to become water vapour.  As a general rule, the drier the air the more effective this evaporation process will be. Under more humid conditions, there will be less effective evaporation and so contrails will generally last longer in more humid air. Contrail formation is also influenced by wind speeds, with higher winds disrupting and breaking up contrail formation.

Contrails do not adversely impact ambient air quality in Ireland. Met Éireann advises that there is some evidence that contrails can influence climatology but they have little impact on day-to-day weather. The purported reason for the former is that the contrails (or consequent cirrus cloud) will trap outgoing long-wave radiation, thus leading to warming in the atmosphere, and that this effect is greater than the reflection of short-wave radiation from the sun.