Corrosive effects from the deposition of gaseous pollutants on surfaces of cultural and artistic value inside museums

Effect of a SO2 Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints

The behavior of historic tempera paints exposed to pollutant gases is an important issue when developing conservation strategies. In this work, binary tempera paint mock-ups that were made with either smalt or lapis lazuli pigments mixed with either rabbit glue or egg yolk binders were exposed to an SO2 accelerated aging test in order to find out more about the forms and mechanisms of alteration resulting from pigment-binder interaction. To this end, spectrophotometry, hyperspectral image analysis, and profilometry were used to study macro-scale, physical changes taking place on the surface of the paints, affecting color, gloss, reflectance, and roughness. Likewise, chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (ATR-FTIR), polarized light microscopy (PLM), and scanning electron microscopy with micro-analysis (SEM-EDS), which was also used to visualize micro-texture changes in the paints. The smalt-based tempera showed a higher degree of deterioration than the lapis lazuli-based tempera, in particular a notable whitening related to the precipitation of sulfate-rich salts and to binder and pigment chemical alterations. Moreover, whereas aged egg yolk-based paints showed visible color change due to damage to the oily binder and the pigments, the most evident change in rabbit glue-based paints was binder loss. The alteration suffered by the pigments varied in line with their composition; thus, smalt (blue cobalt-containing glass) grains were more sensitive to SO2 exposure than lapis lazuli-(Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]-crystals. In the smalt grains, the SO2 test caused K+ leaching from the glass matrix, which was detected by means of K/Co ratios, but the lazurite crystals (main component of lapis lazuli) were unaffected (regardless of the binder used in the tempera). The most likely source of the crystallized sulfate rich salts were the impurities that were detected in association with the natural lapis lazuli pigment, i.e., calcite and diopside. Indeed, the precipitation of efflorescences is the main cause of the optical changes found in the smalt- and lapis lazuli-based tempera, in addition to the physical-chemical damage to the binders. The information reported here would be useful for preventive conservation, as well as for art restorers, who are planning work on paintings in which paints of this kind were used.

Assessing indoor gas phase oxidation capacity through real-time measurements of HONO and NOx in Guangzhou, China

The hydroxyl radical (OH) is one of the most important oxidants controlling the oxidation capacity of the indoor atmosphere. One of the main OH sources indoors is the photolysis of nitrous acid (HONO). In this study, real-time measurements of HONO, nitrogen oxides (NOx) and ozone (O3) in an indoor environment in Guangzhou, China, were performed under two different conditions: (1) in the absence of any human activity and (2) in the presence of cooking. The maximum NOx and HONO levels drastically increased from 15 and 4 ppb in the absence of human activity to 135 and 40 ppb during the cooking event, respectively. The photon flux was determined for the sunlit room, which has a closed south-east oriented window. The photon flux was used to estimate the photolysis rate constants of NO2, J(NO2), and HONO, J(HONO), which span the range between 8 × 10-5 and 1.5 × 10-5 s-1 in the morning from 9:30 to 11:45, and 8.5 × 10-4 and 1.5 × 10-4 s-1 at noon, respectively. The OH concentrations calculated by photostationary state (PSS) approach, observed around noon, are very similar, i.e., 2.4 × 106 and 3.1 × 106 cm-3 in the absence of human activity and during cooking, respectively. These results suggest that under "high NOx" conditions (NOx higher than a few ppb) and with direct sunlight in the room, the NOx and HONO chemistry would be similar, independent of the geographic location of the indoor environment, which facilitates future modeling studies focused on indoor gas phase oxidation capacity.

Time-Resolved Measurements of Indoor Chemical Emissions, Deposition, and Reactions in a University Art Museum

A 6-week study was conducted at the University of Colorado Art Museum, during which volatile organic compounds (VOCs), carbon dioxide (CO₂), ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂), other trace gases, and submicron aerosol were measured continuously. These measurements were then analyzed using a box model to quantify the rates of major processes that transformed the composition of the air. VOC emission factors were quantified for museum occupants and their activities. The deposition of VOCs to surfaces was quantified across a range of VOC saturation vapor concentrations ( C*) and Henry's Law constants ( H) and determined to be a major sink for VOCs with C* < 10⁸ μg m^-3 and H > 10² M atm^-1. The reaction rates of VOCs with O₃, OH radicals, and nitrate (NO₃) radicals were quantified, with unsaturated and saturated VOCs having oxidation lifetimes of >5 and >15 h, making deposition to surfaces and ventilation the dominant VOC sinks in the museum. O₃ loss rates were quantified inside a museum gallery, where reactions with surfaces, NO, occupants, and NO₂ accounted for 62%, 31%, 5%, and 2% of the O₃ sink. The measured concentrations of acetic acid, formic acid, NO₂, O₃, particulate matter, sulfur dioxide, and total VOCs were below the guidelines for museums.

Impacts of potential HONO sources on the concentrations of oxidants and secondary organic aerosols in the Beijing-Tianjin-Hebei region of China

We first coupled indoor emissions and biomass burning emissions into the WRF-Chem model besides the other four potential HONO sources (i.e., traffic emissions, soil emissions, and heterogeneous reactions on aerosol and ground surfaces). Eight simulations were performed in the Beijing-Tianjin-Hebei region (BTH) of China in August of 2006. The results indicated that traffic emissions and heterogeneous reactions on ground and aerosol surfaces were the key sources of HONO at night, accounting for ~41%, ~27% and ~20% of the nighttime simulated HONO concentrations, respectively. The two heterogeneous reactions were the main contributors during the day, accounting for ~66% (ground surfaces) and ~19% (aerosol surfaces) of the daytime simulated HONO concentrations. The indoor emission source could be the second largest contributor during nighttime and led to a maximum hourly enhancement of 0.59 and 0.76 ppb at the central urban sites of Beijing and Tianjin, respectively. The six potential HONO sources enhanced the monthly meridional-mean concentrations of O₃, OH and HO₂ by 5-44%, 5~>150% and 5~>200%, respectively, leading to an enhancement of 1-3 μg m^-3 in the monthly averaged concentrations of secondary organic aerosol (SOA), and that of 10-35 μg m^-3 in the largest hourly concentrations of SOA within 1000 m above the ground in the BTH. The major precursors of the enhanced SOA were Xylenes, Toluene and BIGALK (lumped alkanes C > 3). The inclusion of the six potential HONO sources in the WRF-Chem model considerably improved the HONO simulations at both urban and suburban sites compared with the corresponding observations. The above results suggested that the six potential HONO sources significantly enhanced the atmospheric oxidation capacity and thus accelerated SOA chemical aging in the BTH of China, leading to large enhancements in the hourly SOA concentrations and aggravating haze events in this region.

Air pollution effect of SO2 and/or aliphatic hydrocarbons on marble statues in Archaeological Museums

This study allowed the identification of the main physicochemical characteristics of deterioration of the materials used in the construction of Greek ancient statues in order to plan a correct methodology of restoration. The method of Reversed-Flow Inverse Gas Chromatography is appropriate to investigate the influence of air pollutants on authentic pieces from the Greek Archaeological Museum of Kavala, near Salonica. Six local physicochemical quantities which refer to the influence of one or two pollutants (synergistic effect) were determined for each system. These quantities answer the question "when, why and how materials of cultural heritage are attacked".

Time-resolved chromatographic analysis and mechanisms in adsorption and catalysis

The main object of this review is the study of fundamentals of adsorption and heterogeneous catalysis, a benefit for the understanding of adsorptive and catalytic properties. This work aims to define and record, with the utmost accuracy, the phenomena and the possible reactions. A new methodology for the study of the adsorption is presented, which is a version of the well-known inverse gas chromatography. This reversed-flow inverse gas chromatography (RF-IGC) is technically very simple, and it is combined with a mathematical analysis that gives the possibility for the estimation of various physicochemical parameters related to adsorbent or catalyst characterization, under conditions compatible with the operation of real adsorbents and catalysts. On this base, this methodology has been successfully applied to the study of the impact of air pollutants, volatile organic and/or inorganic, on many solids such as marbles, ceramics, oxide-pigments of works of art, building materials, authentic statues of the Greek Archaeological Museums. Moreover, this methodology proved to be a powerful tool for studying the topography of active sites of heterogeneous surfaces in the nano-scale domain. Thus, some very important local quantities for the surface chemistry have been determined experimentally for many solids including thin films. These physicochemical local quantities (among which adsorption energy and entropy, surface diffusion coefficient, probability density function) have been determined from the experimental pairs of height of extra chromatographic peaks and time by a nonlinear least-squares method, through personal computer programs written in GW BASIC and lately in FORTRAN. Through the time-resolved analysis the surface characterization of the examined materials took place. In addition, the kinetic constants responsible for adsorption/desorption and surface chemical reactions have also been calculated. Thus, important answers have been provided to the following essential questions: (1) Can RF-IGC define the gnostic regions of adsorption/desorption, surface diffusion, surface reaction? Yes, irrefutably and undeniably. (2) Can RF-IGC deal with issues of catalysis, the existence of more than one reaction? Certainly yes. Indeed, it is impressive to observe the reactions "on line". (3) Can RF-IGC identify peaks of products and reactants simultaneously? Certainly yes. (4) Can RF-IGC be applied to thin films in a nano-scale domain? The answer is "definitely yes". (5) Can it kinetically follow the above? Yes, again.

Physicochemical measurements by the reversed-flow version of inverse gas chromatography

Since the first publication on the method, reversed-flow gas chromatography has been used to "separate" physicochemical quantities by measuring the value of one in the presence of another. The experimental arrangement consists of a small modification of a commercial gas chromatograph, so that it includes a four- or six-port gas sampling valve, and a simple cell placed inside the chromatographic oven. This cell suppresses the effects of the carrier gas flow on the physicochemical phenomena taking place in the stationary phase. These phenomena pertain to chemical kinetics, diffusion in gases, liquids and surfaces, mass transfer across gas-liquid and gas-solid boundaries, local adsorption on heterogeneous solid surfaces, etc.

Physicochemical Characterization of Inorganic Pigments in the Presence of Gaseous Pollutants. The Role of Ozone

The Reversed–Flow Gas Chromatography technique was used to study the interaction of volatile hydrocarbons on three inorganic pigments, namely, CdS, ZnS and Cr

Experimental tularemia in Macaca mulatta: relationship of aerosol particle size to the infectivity of airborne Pasteurella tularensis

Ninety-six Macaca mulatta were exposed to aerosol particles containing Pasteurella tularensis. Four different aerosols were employed that contained particle size distributions with median diameters of 2.1, 7.5, 12.5, or 24.0 mum. Size distributions were calculated only for those particles observed by phase microscope to contain organisms. Animals exposed to particles whose median diameters were either 2.1 or 7.5 mum were all infected and showed extensive infection of the lower respiratory tract, evidenced by large patches of consolidation with many necrotic foci on the surface. Death occurred in these animals 4 to 8 days after exposure. Monkeys exposed to 12.5- or 24.0-mum median diameter particles presented involvement of the cervical and mandibular lymph nodes, evidenced by swelling and abscess formation. Thirty-eight of the 45 animals in this group were infected. Those animals succumbing to the disease died from 8 to 21 days after exposure. The respiratory LD(50) values increased from 14 to 4,447 cells as the median diameter was raised from 2.1 to 24.0 mum.