Environmental monitoring is being carried out to determine the impact of fluctuations in temperature and relative humidity on the wall paintings in order to design appropriate climate improvement strategies to stabilize the environment.

Objectives
Objectives of the environmental monitoring are 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 on the wall paintings investigated are: impact of moisture in the wall; condensation; impact of direct and non-direct solar radiation; daily and seasonal humidity and temperature variations; and wind erosion.

Method
Preliminary environmental monitoring was carried out from 2008–2011 consisting of five independent temperature and humidity dataloggers (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 GCI at 15-minute intervals. An extranet site posts current and past environmental conditions.

An autonomous weather station measured exterior conditions from 2011 to 2016.

Exterior parameters and sensor locations
Monitored parameters for the site climate include temperature, humidity, rainfall, solar radiation, and 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 8-ft 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 soil moisture sensor was placed on the undisturbed ground soil and covered by a 10-15 cm pile of soil 20-30 cm southwest from the end of the tablinum's west wall.

Parameters and sensor locations in the tablinum
Parameters for the environment of the wall paintings include sixteen surface temperature measurements at various vertical and horizontal locations on wall 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 walls measurements using sensors installed in November 2011. Both the station and the datalogger 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 different 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.

Development and implementation of passive environmental improvement methods for 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.

Page updated: November 2017