Let it rain! ... or not!

Location of the Acropolis

Being born and raised in Athens, Greece, I grew up hearing all about the Acropolis and its history. Located in the centre of Athens, high on a hill so it can be seen from most of the city centre, but therefore also located in, currently, in the most polluted area of Athens. As a child I was surrounded by people who spoke so passionately about it and how proud they were that even though Greece's reputation might of been dispirited (due to the economic crisis) they will always have their history to be proud of. A history which nobody can take away from them.. OR CAN THEY?

The Parthenon

Acid rain is a world wide problem. Since the industrial revolution, pollutants have been emitted into the atmosphere at an accelerated rate, especially Sulfur(SO2) and Nitrous Oxide(NOx). These acidic compounds  are sourced from natural sources such as volcanic eruptions and lightning respectively, but its the atmospheric emissions which have caused abnormal amounts to persist in the atmosphere and mix with the atmospheric H20. When they mix with water particles in the atmosphere they decrease its pH. Thus, in effect, when the water particles precipitate they have a much lower pH than normal. This acidity can have very damaging effects on various human and environmentally constructed components on the planet. Rain in areas far from industrial sources and hence their pollutants is known to have on average a pH of 5(Schindler, 1988). Any pH lower than this will start reacting with materials and causing damaging effects.

Anthropogenic sources include electric power plants and vehicles. Production of electricity is however the major source. Many techniques to prevent these effects have been tried but not many have been successful. For example, making the smoke funnels taller, but that unfortunately resulted in the smoke being able to travel even further! Therefore, policies had to be implemented worldwide, but the US and Europe were particularly successful in reducing their NOx and SO2 emissions over several decades (Figure 1). Luckily this also correlated with a decrease in acid rain and a noticeable recovery in lakes and streams (EPA). Hence, the only truly successful measure that can be implemented is to reduce emissions;

Which is one of the reasons you are told to "TURN OF THE LIGHTS when you aren't in the room!"

Figure 1: Total Sulfur Emissions over time

The parthenon has 'semi' survived the effects of bombs, fires and earthquakes! Could a little big of rain really be enough to destroy it forever? The parthenon is made of beautiful white marbles (essentially limestone), and it is now turning black and being corroded!! This is not only because of the acid rain reactions but also because of the black fumes coming out of vehicles (but this is a matter for a different day). The question is how to preserve the sculptures as best as possible without losing the incredible detail (Figure 2)? Limestone is very sensitive to acidity, which corrodes it very productively (Kucera,1994). Therefore as discussed above the only guaranteed ways of reducing these effects is for the Greek government to either enforce policies which will reduce the people total electricity usage, or to implement alternative energy sources other than fossil fuels which do not pollute the atmosphere. 

Figure 2: Battle of the centaurs, depicted on the metopes of the Parthenon

Currently, they are attempting to clean as much of the monument as they can using laser treatment which combines UV and Infrared beams (Daily Mail, 2008) Figure 3 below, shows the effects of the treatment on the marbles( left side is cleaned, right side is still black). But this only works in reducing the effects of smog, and not the effects of corrosion. Once the marble is corroded it is lost forever.

Figure 3: Cleaning using the laser technology.

The parts from the Acropolis temples which have been taken into museums (Acropolis museum, Athens and British museum), have parts missing due to the damage of the earthquakes and of the bomb. New marble has hence been replaced to fill in the gaps. This however not only looks artificial, as the new marble is so much whiter than the ancient one, but the detail can not be replicated. Therefore, the only solution for the corroded marble in the future will be to do the same which will eventually lead to more of it being replaced and the genuine history being lost.

So, in the future, to save the history of Athens, either all of the acropolis will have to be taken apart and placed in the protection of museums, or there will have to be a significant reduction in the amount of pollution emitted in Athens.