Oxygen Masks Will Drop From Above

Following on from the ways in which nitrogen oxides, released from aircraft alter the chemistry of the atmosphere, as was discussed in the previous post, I am going to focus on a paper I found (Barrett et al. 2010), that discuses the human health implications of these and other aviation related emissions. 

Passengers in planes aren't the only people who need oxygen masks!

The study finds that there are around 8000 annual premature mortalities attributable to emissions released by aviation, and which alter air quality. Such emissions can effect widespread areas of the world despite originating in isolated regions and corridors. A lot of this is due to global atmospheric circulation - which conveniently helps to funnel down the harmful and polluting chemicals into the lower troposphere so we can all benefit from them too.

The figure below taken from the paper describes how aircraft emissions in the upper troposphere in the Northern Hemisphere interact with existing circulation patterns. Peak aircraft emissions occur in the Ferrel atmospheric circulation cell. Air mixed with pollutants released from aircraft in this cell experiences subsidence at 30ºN latitude - as is shown by the brownish line in the Figure. 

(Barrett et al. 2010)

The truly global nature of the way aircraft emissions are spread around the world are explored in the paper. Impacts specifically to humans are linked by pointing aircraft attributable aerosols as responsible for around 3500 premature deaths in India and China despite their relatively low contribution to aircraft emissions. Their geographic location (at around 30ºN latitude) in relation to this atmospheric circulation is believed to be a large determining factor of this.  India for example experiences 7 times more deaths in relation to its aircraft emissions compared to the United States which experiences 7 times fewer deaths. It must be noted however that the number of premature deaths generated for India and China also takes into consideration background ammonia and the high population density in this region.

The paper quotes some quite alarming numbers of premature mortality aircraft cause, which admittedly isn't my top go to cloud gazing topic to think about when I do get the chance to fly (and a window seat), the paper does not really go beyond quoting numbers, and I imagine it is difficult to pin point premature mortality on aircraft emissions, given that their effects probably get manifested in various medical conditions? There is not much to compare such a study too either. Despite this, the study confirms that it is not only take off and landing emissions, close to ground level that are able to have an impact, and that emissions emitted at cruising altitudes are also able to exacerbate the balance of toxic chemicals lower down in the atmosphere. 

In case you haven't had the pleasure of studying Weather and Climate  - the following diagram simplifies global atmospheric circulation, the Ferrel cell that was referred to earlier is marked on. (Taken from the Met Office).

Don't Get On The Wrong Side of An Oxide

Despite contrails being the most visible indication of the impact aircraft are having on the environment, they are certainly not the only form of pollution. In my first post, I touched upon the impacts of CO₂ being released however, they are not the only emissions of environmental significance. The potent nitrogen oxides (NO_x) and sulphur oxides (SO_x) are also released, albeit in smaller quantities as CO₂ but with potentially more damaging consequences. I must mention that these pollutants contribute to the formation of contrails and the modification of natural cirrus clouds too, for the sake of being able to mention contrails again!

Today, I am going to be looking at the well documented effects of nitrogen oxides. NO_x emitted from aircraft today are 5 times more efficient at affecting the global ozone burden than emissions originating from ground transportation such as road vehicles (Hauglustaine and Koffi 2012). In spite of its higher potency as pollutant than CO₂, the radiative forcing of NO_x is relatively small as described in Fuglestvedt et al. (2009), Myhre et al. (2011), and Holmes et al. (2011). This is as a result of the opposing effects it has on ozone and methane in the atmosphere. 

NO_x from aircraft promotes the formation of ozone (O₃) in the troposphere and lower stratosphere. Ozone has a positive radiative forcing (i.e a warming effect). This enhancement of ozone is offset by the chemical alterations NO_x has on the oxidising capacity of the atmosphere. NO_x cause an enhancement of the oxidising capacity, which reduces the lifetime of atmospheric methane (CH₄). This reduction in  methane leads to a negative forcing (i.e a cooling effect). Less methane also means less ozone is produced. This renders nitrogen oxides a forcing agent that is able to affect the chemistry of the atmosphere. 

Although the effects of NO_x released by aircraft may not seem that bad, Köhler et al. (2008) investigated the disturbances to methane and ozone in the atmosphere as a result of nitrogen oxide input from aircraft. They concluded impacts varied depending on the altitude of the aircraft for example, a plane flying at 11 km would lead to an ozone increase of 200% and a reduction in methane lifetime per emitted mass of  NO_x, 40% as strong as a plane flying 5 km altitude. 

The study also found that much like how the effect of ground based NO_x emissions affect atmospheric ozone and methane differently depending on their geographic location, the same applies to aviation. The geographic distribution of NO_x emissions has consequences for flight route planning, and it is predicted that growing aviation in Asia could lead to significant impacts regarding methane and ozone within the troposphere, even if emissions were to remain constant. 

This raises important questions as to what impact future increases in air travel will have as new flight routes open and increase in frequency, especially considering the planning currently involved in reducing the effects of emissions on the atmosphere. Also how strategies accounting for these harmful types of pollution will continue to be managed. 

How to plan for more planes?

Chemtrails

During my search for information on contrails for the previous two posts, one word kept on coming up which didn't seem to want to go away: chemtrails. 

It is not very scientific of me to be doing a post on them, as you will see! but it was so persistent a word (try searching chemtrails for yourself!), that I thought I would do some digging...

Chemtrails are part of a conspiracy theory. It is the belief that governments are using  aircraft to spray chemical or biological agents for numerous top secret reasons. It is thought they are unlike contrails because they are longer lasting. Just in case all sorts of questions are racing through your mind at this point, rest assured that we in the UK are safe. Earlier this year, UK government via the Department of Energy and Climate Change stated that the "UK population is not being sprayed" after a freedom for information request. 

We all need an education  

Surprisingly, I could not find many scientific articles or journals on the matter. I managed to find an article in Australian Science, in an article entitled 'Chemtrails - Conspiracy theory?'. In it the contents of an hour long video entitled 'What in the World are they Spraying?' made by political activist Michael Murphy are addressed - especially the release of aluminium and its consequential health effects.

It is unlikely we will find evidence for the nanobots being deployed into the atmosphere via aircraft to modify the weather as the link below the picture above describes. Saying that, I found news articles from the BBC and Guardian reporting on how previously classified documents have suggested that experimental cloud seeding conducted by the RAF that was occurring at the beginning of the 1950s were partly responsible of the 1952 floods at Lynmouth, in which 35 people were killed. It remains an allegation that has not been proved. Early scientific studies such as Cooper and Jolly, 1970 have suggested that the sustained use of silver iodide in cloud seeding could have detrimental effects on some ecosystems, and that there was a responsibility to monitor the environmental impacts of such technology. 

I'll let your thoughts simmer whilst you watch this video...