Roger A. Lefèvre

Embryonic sulphated black crusts on carbonate rocks in atmospheric simulation chamber and in the field: role of carbonaceous fly-ash

Experimental conditions characteristic of the urban pollution in many European cities over the last decades were reproduced in a simulation chamber in which samples of limestone were exposed for a period of 12 months, both naked or sprinkled with carbonaceous fly-ash. In agreement with the findings reported in the literature the fly-ash emitted by heavy fuel combustion are highly reactive, undergoing chemical and morphological transformations which give rise to crystals growth, especially gypsum. The development of gypsum crystals was observed overall in close proximity of fly-ash anchoring them to the limestone surface. Samples of the same limestone exposed in the field in a polluted environment for the same period of time led to similar results. The preliminary mechanisms leading to the genesis of sulphated black crusts in polluted environments were thus highlighted. Because of their roughness the embryonic black crusts increase the development of the crust by trapping new particles. This trapping is also facilitated by the wetness of the stone surface leading to the development of hydrated mineral (gypsum) in the water meniscus between fly-ash and stone surface.

Experimental study of limestone and sandstone sulphation in polluted realistic conditions : The Lausanne Atmospheric Simulation Chamber (LASC)

Abstract The Lausanne Atmospheric Simulation Chamber (LASC) has been constructed with the aim of studying the SO2 effects on different materials. It allows the carrying out of numerous measurements on large stone samples simultaneously and on line. The behaviour of two carbonatic stone types (limestone and sandstone), either naked or covered with fly ash or soot particles, exposed at the following conditions, SO2 = 125 ppb (340 μg m−3), NO2 = 50 ppb (98 μg m−3), relative humidity = 79%, temperature = 13°C, has been studied. This experiment has been carried out over a 1 yr period. It has been observed that SO2 deposition velocity decreases with time and in different ways for each of the two stone types, naked or covered with fly ash or soot particles. During the first four months, the deposition velocity is higher on naked stones; later on, it is higher on the stone samples covered with fly ash. Throughout the experiment the SO2 deposition velocity on stone samples covered with soot particles is lower than on naked samples and those covered by fly ash. Finally, the values of SO2 deposition velocity are confirmed by the chemical analysis of sulphur in the samples. Sulphur is present from the stone surface down to about 0.8 mm depth.

Recording of pre-industrial atmospheric environment by ancient crusts on stone monuments

The interaction between today’s polluted urban atmosphere and materials leads to the formation of sulphated black crusts containing industrial fly-ash. While many historical documents report the existence of polluted air in towns prior to the modern industrial era, such descriptions have not so far been substantiated by any scientific analysis of samples of older interactions. A new approach is proposed, based on the study of crusts found in Arles and Bologna, which formed in the periods 1180–1636, and 1530–1887, respectively. They are grey, mostly calcitic, and contain wood debris and micrometric siliceous or alumino-silicated spherules. The same tracers were also encountered in the smoke from experimental wood fires. This approach confirms the presence of air polluted by wood combustion in the towns of Southern France and Northern Italy during the Medieval up to pre-industrial age. Such information, near to the source, completes the evidence provided in written documents, as well as the data obtainable, farther from the sources, using core samples of glaciers, lakes and marine sediments.

Experimental rapid alteration of basaltic glass: Implications for the origins of atmospheric particulates

Glassy microspherules collected from the plume of Etna volcano show a surprising compositional variability with SiO 2 from 48 to 90 wt%, despite a very homogeneous basaltic source magma (SiO 2 = 48%). This same variability is also observed in individual microspherules from their inner to outer parts. The most plausible hypothesis concerning these compositional variabilities is the interaction of the microspherules with the volcanic gases inside the crater prior to their atmospheric dispersal. In order to study this compositional variability we experimentally exposed basaltic glass to volcanic gases at Etna. The resulting glass composition documents a fundamental alteration mechanism, involving an apparent leaching process that can rapidly form nearly pure silica. Because microspherules erupted directly into the air from lava fountains remain unaltered, the duration of microspherules within a gas plume can explain the chemical variability of glass alteration. A major implication for the origin of glassy atmospheric particulates is that chemical compositions cannot be used as a reliable indicator of their source (e.g., meteoric, volcanic, anthropogenic).

Air pollution records on selenite in the urban environment

Abstract Black crusts (BC) on selenite, i.e. gypsum stone used in buildings and monuments in the city of Bologna (northern Italy) have been studied. The crusts have been compared with genetically identical ones encountered on gypsum outcrops in the area surrounding the same city, in a relatively clean rural environment. Because of gypsums high solubility, also in the past, BC began to form and embed particles of atmospheric aerosol as soon as the stone was used in construction, even though the SO 2 levels in the air were probably much lower than today. Unlike other types of stone (sandstone, limestone, marbles), selenite is currently undergoing a deceleration of dissolution processes, following the acidification of the environment caused by industrialisation. For this reason the BC on selenite are older (up to 580±45xa0yr), thicker (up to 4xa0cm) and far more stable than those encountered on other types of building stones used in the same area. The BC are stratified: at the base, in contact with the stone, the crust contains numerous prismatic black particles originating from wood combustion; immediately above the base layer these particles progressively increase; finally, in the outer part of the crust one encounters the characteristic black, spongy spherical fly-ash originating from the combustion of mineral oils. From the chemical point of view, a comparison between urban and rural crusts shows that elements such as C, Si, K, Fe, V, Cr, Ni, Zn, Ga, As and Pb are due to present-day and/or past pollutant sources within the city itself. Moreover, the chemical data from the stratigraphy of the BC show that, while C and K were more abundant in the past than now, elements such as Fe, V, Cr, (Mn, Ni), Cu, (Zn), (Ga), As, Pb characterise recent and current urban atmospheres.

Evidence of pre-industrial air pollution from the Heads of the Kings of Juda statues from Notre Dame Cathedral in Paris.

Pollution originating from wood combustion characterised the urban atmospheres of the past and led to the formation of thin grey crusts on the surface of the stone of monuments. The grey crusts discovered on the Heads of the Kings of Juda statues, which adorned the facade of Notre Dame in Paris from the 13th century until 1792, constitute a material record of the effects of this ancient air pollution. The height at which the statues stood suggests that the effect was not the result of a point phenomenon, but was caused by a generalised pollution of the Paris atmosphere at the time.

Early mechanisms of development of sulphated black crusts on carbonate stone

Publisher Summary Carbonaceous fly-ash, particularly those emitted by heavy fuel oil combustion, has a strong physicochemical reactivity. They contain many sulfured chemical species, in particular sulfates along with metals such as vanadium, iron, and nickel. This chapter describes the role of carbonaceous fly-ash in the nucleation of gypsum crystals and in the development of incipient sulfated black crust on carbonate surface. This study is conducted by comparing simulation chamber data with those obtained in the field. Embryonic black crust forming over 12 months through interaction between carbonaceous fly-ash and samples of Jaumont limestone in the controlled atmosphere of a simulation chamber are compared with those forming in the field on the same carbonate stone, over the same time period in a real polluted atmosphere. The Jaumont limestone samples were placed inside the LASC, either naked or sprinkled with fly-ash. Similarly, Jaumont field samples were collected and examined with ASEM. The chapter discusses the results from both samples and compares them to draw conclusions. On the basis of simulation chamber and field data obtained over 12 months, the study of the morphology, mineralogy, and chemical composition of the deposits and associated neocrystallizations indicates that they represent the first stage of black crust development. The fly-ash appears to play a crucial role in the formation of black crusts because they facilitate the precipitation of gypsum, which constitutes the predominant mineral in the black crusts.

Past air pollution recordings on stone monuments: The Heads of the Kings of Juda Statues from Notre-Dame Cathedral (Paris)

Publisher Summary Pollution linked to the combustion of wood is characteristic of the atmosphere of the cities in the past. It led to the development of thin grey crusts on the surface of the stones of monuments. The grey crusts were discovered on the Heads of Kings of Juda Statues, present on the western facade of Notre-Dame in Paris from the 13 th Century to 1792. These thin grey crusts are the material witnesses of the effects of the ancient air pollution, prevalent during the French revolution and the period immediately before it. This chapter focuses on the research conducted on the character and evolution of urban air pollution in the past; and the comparison of results with those derived from studies on the modern industrial black crusts. Several analytical techniques were used to highlight the main physicochemical and mineralogical characteristics of the grey crusts: colorimetric technique, X-ray diffraction, and photon microscopy. Many of the characteristics of the ancient grey crusts of the Heads of Kings of Juda directly contrast with those of the modern day black crusts: color, texture, thickness, and chemicomineralogical nature of the crusts and of the prismatic or spherical particles embedded in the matrix. Diffractometric analysis of the modem black crusts highlights the presence of the same minerals as those found in the ancient crusts of the Heads, but in different proportions greater amounts of gypsum than calcite, followed by quartz and weddellite. A further major difference between the ancient grey crusts and the modern black crusts lies in the kind of particles contained in the gypsum-calcite cement. While the grey crusts only contain the residues of incomplete wood combustion, the modern crusts embed microspheres, which turn out to be fly-ash released into the atmosphere by the combustion of coal or heavy fuel.

ATMOSPHERIC ALUMINO-SILICATE MICROSPHERULES INSIDE THE BLACK CRUST OF ALTERED LIMESTONE AT FONTEVRAUD ABBEY (FRANCE)

Summary The limestones (“tuffeau”) of the ”Cloitre du Grand Moutiers” and the “Salle Capitulaire” in the Fontevraud Abbey (Loire Valley, France) contain two types of mineral microspherules : - in the non-altered substrate stone : microspherules (10 μm in diameter), only siliceous in composition and probably biogenic in origin. - in the altered black crust : alumino-silicate or metallic microspherules (1-5 μm in diameter) associated with gypsum crystals. A study by means of Analytical Scanning Electron Microscopy has been performed on the microspherules both in non-altered and altered stone. The chemical composition of the microspherules associated with gypsum is the same as that of industrial fly-ash emitted by coal-burning power plants. Their presence in the altered crusts of carbonatic rocks is in agreement with a previous study. Their role in the formation of the sulphate crust is probably of major importance. The origin of fly-ash has been studied by back trajectories of air masses during the sampling period.