Environmental Monitoring and Climate Improvement Strategies

Objectives of the environmental monitoring were to assess environmental conditions in the tablinum of the House of the Bicentenary and its wall paintings and to identify environmental threats to their preservation, as well as to develop and test several strategies for environmental improvements for efficacy and applicability.

Specific issues investigated on the wall paintings were the impact of moisture in the wall; condensation; the impact of direct and nondirect solar radiation; daily and seasonal humidity and temperature variations; and wind erosion.

Preliminary environmental monitoring was carried out from 2008 to 2011, consisting of five independent temperature and humidity data loggers (Hobo Prov2) placed throughout the house to record temperature and humidity variations and investigate sources of high humidity affecting the wall paintings in the tablinum.

In 2011 a solar-powered autonomous environmental monitoring station, which measures the site climate and environmental conditions of the walls and the wall paintings in the tablinum, was installed to conduct more focused measurements. Data from the online monitoring are autonomously downloaded by the Conservation Institute at fifteen-minute intervals. An extranet site posts current and past environmental conditions.

Monitored parameters for the site climate include temperature, humidity, rainfall, solar radiation, wind speed, and wind direction. All the climate sensors, except for the wind speed and direction, were mounted outside the tablinum in the peristyle garden. The wind sensor (R.M. Young Inc, Wind Monitor) was installed on an eight-foot tripod erected on the tablinum roof. Since the circulation area between the tablinum and the peristyle garden has an archaeological foundation for a mosaic floor, the ground soil could not be disturbed to place a soil moisture sensor. Therefore, a sensor was placed on the undisturbed ground soil and covered by a 10- to 15-cm pile of soil 20–30 cm southwest from the end of the tablinum's west wall.

Parameters for the environment of the wall paintings include sixteen surface temperature measurements at various vertical and horizontal locations on surfaces of the wall paintings, sixteen temperature and humidity measurements at the core of the tablinum walls, four surface-temperature measurements of medallions, and six locations for time-of-wetness of wall measurements using sensors installed in November 2011. Both the station and the data-logger systems operated from installation until 2016, when the first phase of environmental monitoring was completed.

Three ultrasonic wind sensors were positioned in and around the tablinum. At different times, they were arranged in various configurations in the tablinum and in adjacent rooms to measure the symmetry/asymmetry of the air flow pattern in the tablinum; to measure effects on the air flow pattern of the opening to the garden as well as the atrium; and to measure relative air flow changes through the tablinum, triclinium, and the corridor once a screen door was installed in the tablinum.

Based on the information gleaned from the environmental monitoring, the project team, in collaboration with the Soprintendenza Pompei and Herculaneum Conservation Project, designed and installed a screen door at the garden side of the tablinum to reduce and mitigate high fluctuations of relative humidity and air temperature, and for protection from wind, rain, and light exposure on the wall paintings. Currently, different screen materials are being tested on site.