Variability of Biocide Emissions from Building Facades Based on Meteorological Data

Biocides are used extensively in urban settings for façade coatings, roof waterproofing, and termite control. During rainy weather, they are released into building runoff, causing negative impacts on aquatic and terrestrial ecosystems. Prior studies mainly focused on laboratory experiments or small-scale contexts. Urban-scale modeling, however, has rarely been explored. This is due to the complexity of biocide behavior, the spatiotemporal variability of emission factors, and the limited knowledge about biocide use and existing stocks within the urban critical zone. Our objective is to assess the stock potential and emission potential of biocides from building envelopes in the Parisian conurbation. We also aim to develop and implement a model at the urban scale to evaluate the fluxes of biocides emitted in runoff water from building facades. One of the main factors that significantly influences the emissions is the wind-driven rain (WDR), which directly affects the volume of water runoff on building facades. Since emissions strongly depend on WDR, precise modeling needs adequate meteorological data, especially for extensive metropolitan regions. Our research focuses on the Île-de-France region, a heterogeneous and extensive urban area. This study examines the variability in meteorological data—namely precipitation, wind speed, and wind direction from nine stations located across the area (Acheres, Le Bourget, Longchamp, Magnanville, Orly, Paris Mont-Souris, Roissy, Trappes, and Villacoublay). By analyzing the data from these stations, we seek to quantify the variability in meteorological conditions across the area; evaluate the influence of these variations on cumulative biocide emissions; and assess the potential enhancement of accuracy and reliability in emission estimations by the combination of data from various stations.

To estimate biocide runoff from facades, we will develop scenarios on COMLEAM, a software program created by HSR (Hochschule für Technik Rapperswil) that simulates the leaching of hazardous compounds from building materials subjected to environmental conditions. The scenario used considers a building with eight façades oriented in primary compass directions made of render matte containing encapsulated terbutryn. Leaching behavior is approximated using mathematical functions from experimental data. As our investigation will not include an experimental component, we will depend on those suggested by COMLEAM, particularly the logarithmic function, which has been shown to be the most effective for characterizing biocide emissions. The emission function applied for terbutryn follows a logarithmic relationship derived from field studies in Zurich.

The findings demonstrate WDR's strong effect on biocide emissions, with important variation between measurements of each station. Two extremes were identified: Roissy had the highest cumulative WDR (200 L/m² from South-West) and emissions (~11,000 mg), whereas Acheres had significantly lower WDR (70 L/m² from South-West) and emissions (~7,000 mg). The others had comparable findings, with a total WDR of 140 L/m² and emissions of 10,000 mg over 10 years. These results also highlight the importance of the measurement station's location, as open-space stations (e.g., Roissy) exhibited higher WDR due to reduced shielding. From this study, we deduce that using large-scale meteorological data introduces biases, making meteorological parameter refinement essential for improving accuracy.