Author: Donovan Dennis
When taking in a sunset from Fiji Hill, it’s hard not to appreciate a little bit of Los Angeles’ smog. The golden sunlight, breaking through afternoon rush-hour fumes, paints the sky pastel, inspiring a proliferation of no-filter Instagrams — #ouchmylungs.
While atmospheric concentrations of greenhouse gases may be reaching dramatic new levels, regional air quality in the U.S. and Europe has, in fact, generally improved as the health impacts of smog and car exhaust have become better understood.
Though not the primary beneficiaries, the world’s most ancient buildings and monuments are thanking us.
Marble is highly desirable as a material for buildings and sculpted stone not only for its aesthetic qualities, but also for its relative softness compared to other stones. Its malleability, a product of its biologic beginnings, allows for the carving and architectural manipulation that have led to the many famous marble works known today.
Every beautiful marble façade, however, was once a beautiful coral reef. As corals accumulate over time in marine environments and eventually die off, they are preserved in the sedimentary record as limestones. When buried deep below the surface and subjected to high pressure or temperature conditions, the limestones metamorphose into marbles.
As marbles come from deep underground, its most vicious aggressor fittingly falls from above. Sulfur dioxide, when mixed into the low atmosphere, reacts with water and oxygen in the air to form sulfuric acid. Like hydrochloric acid and human flesh, sulfuric acid and marble do not play well together. When calcium carbonate (CaCO3), the primary constituent of limestone/marble, interacts with sulfuric acid (H2SO4), the negatively-charged SO4 switches place with the also negatively-charged CO3. This chemical do-si-do results in CaSO4, CO2 and H2O — none of which add up to equal marble.
Chronic pollution in India has caused the surface of the Taj Mahal to yellow, and recent conservation plans have come up short in protecting its originally pearly surface. As industrial development brought more cars and power plants to India’s urban areas — a phenomenon still occurring today — government officials spent millions of dollars to protect one of the most recognizable monuments in the world, largely to no avail. New Delhi and other urban areas across Asia are facing the mounting challenges of increased pollution, and their many public monuments are already feeling the effects of acid rain.
Fortunately for admirers of ancient architecture, atmospheric concentrations of sulfur dioxide in North American and Europe have decreased since the sweeping anti-pollution legislation of the 1970s. Though current levels still pose a threat to the integrity of ancient marble buildings like the Parthenon, continued capping of these and other gasses that lead to acid rain (nitrogen oxides, notably) will continue to lower the threat.
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