Safeguarding outdoor cultural heritage materials in an ever-changing troposphere: Challenges and new guidelines for artificial ageing test

Outdoor Cultural Heritage (CH) suffers severe damage due to the interaction amongst physical and chemical atmospheric factors. To study the mechanisms of degradation and to test the effectiveness of experimental protective treatments, accelerated ageing tests and artificial rains are widely used. In a scenario where climate and tropospheric composition are changing, the compositional variation of atmospheric deposition might strongly contribute to a gap between the results obtained in laboratory and real-world outdoor exposure. To reduce this gap, updated synthetic solutions, representative of changed deposition, seem necessary for material testing so to set up better conservative strategies. This study provides new formulations of ageing solutions representative of changed deposition in southern Europe, obtained through the analysis of trends and sources of ions in atmospheric bulk depositions (1997–2019 period) collected in a highly polluted area (Po Valley, Italy).