Invisible agents are attacking precious works of art in Italian museums, dissolving paintings and eroding statues, according to a report published on Tuesday by a leading environmental group.
The study by Legambiente, which tested air quality inside 15 museums across Italy, warned that dust, ozone and poisonous gases are causing irreversible damage to the country's cultural heritage.
"Every day, works of art held in Italian galleries are exposed to the threat of degradation as a result of the smog clogging the air in city centres," said Legambiente chief Francesco Ferrante.
"Museums, designed to protect historic artworks from the ravages of time, are not always able to resist the pressure of atmospheric pollution, which penetrates the walls and alters the quality of the interior atmosphere".
The study, sponsored by the culture ministry, found that the Paduan Museum of River Navigation was the worst affected of the 15 institutes.
Levels of ozone inside the museum were 20 times above legal limits, partly as a result of high pollutant emissions from a nearby highway, combined with solar radiation. The effects of ozone on certain pigments in art is similar to that of hydrogen peroxide, bleaching the colours from the paint.
The Museum of Oriental Art in Rome also had high ozone levels, at 18.55 times above the limit.
Although showing lower levels of ozone, the situation inside Naples' famous National Archaeological Museum was equally serious, with nitrogen dioxide levels 15 times above safe levels.
Worryingly high levels of nitrogen dioxide were also recorded at the Italian Risorgimento Institute in Rome (10.6 times above the limit) and at the Contemporary Art Pavilion in Milan (9.3 times).
In general, sulphur dioxide pollution was well within safe levels. However, the study stressed this was perhaps because it was mainly emitted by central heating, meaning levels are likely to rise over the winter.
The effects of the noxious gases and fine dust are impacting artworks in a variety of ways, depositing layers of dirt, covering bas reliefs in grime, eroding and fading paintings, causing wood to swell and blackening marble, said the report.
"The results of these tests mean we are launching an appeal to the directors of Italy's museums, asking them to work alongside environmental associations to ensure cleaner air in our cities," concluded Ferrante.
"This is crucial first and foremost for the health of the people living there but it is also vital in order to protect Italy's priceless and irreplaceable artistic heritage".
Air pollution has been considered a possible cause of damage to museum collections for over 100 years.
Concern over the impact of London smog led to the first comprehensive series of tests on artwork in 1888, examining whether exposure to the combustion exhaust from a burning gas jet would cause paint pigments to fade.
