Atmospheric Deposition and Conversion of Ammonium to Nitric Acid on a Historic Building: A Pilot Study

Abstract

Dry and wet deposition on a church tower at Schagen, The Netherlands was estimated by means of sampling with exposure panels. These panels contain several test stones and the runoff water was collected for each stone separately. The runoff samples were analyzed for: Cl⁻, NO₃ ⁻, NH₄ ⁺, SO₄ ²⁻, Na⁺, K⁺, Ca²⁺ and Mg²⁺. They were located at a height of 20m on the West and East side of the tower during a pilot study of seven months. The concentrations of gaseous HCl, HNO₃, NH₃, SO₂ and Cl⁻-, NO₃ ⁻-, NH₄ ⁺ – and SO₄ ²⁻-containing aerosols in air were measured during this field experiment. Precipitation was sampled by means of bulk and wet-only samplers. It is concluded that: (1) Passive sampling by means of exposure panels and analysis of the runoff is a simple method to estimate the total deposition on a monument; (2) acid-deposition-related air pollutants are deposited on the church tower for more than 80% by dry deposition; (3) as a result of the increased turbulence around the church tower, acid dry deposition is increased by at least a factor 10 compared to lower vegetation. The role of ammonium deposition was studied by means of a ¹⁵N-enriched ammonium solution added to the surface of stone samples. An increase is observed in the ratio ¹⁵N/¹⁴N in nitrate extracted from the stones. This indicates nitrification of ammonium to nitric acid, which results in increased weathering of a monument by the deposition of ammonium.

Key Words:

• Dry and wet deposition
• acid deposition
• monuments
• nitrification