Sasho Gligorovski

Environmental Implications of Hydroxyl Radicals (•OH)

The hydroxyl radical ((•)OH) is one of the most powerful oxidizing agents, able to react unselectively and instantaneously with the surrounding chemicals, including organic pollutants and inhibitors. The (•)OH radicals are omnipresent in the environment (natural waters, atmosphere, interstellar space, etc.), including biological systems where (•)OH has an important role in immunity metabolism. We provide an extensive view on the role of hydroxyl radical in different environmental compartments and in laboratory systems, with the aim of drawing more attention to this emerging issue. Further research on processes related to the hydroxyl radical chemistry in the environmental compartments is highly demanded. A comprehensive understanding of the sources and sinks of (•)OH radicals including their implications in the natural waters and in the atmosphere is of crucial importance, including the way irradiated chromophoric dissolved organic matter in surface waters yields (•)OH through the H2O2-independent pathway, and the assessment of the relative importance of gas-phase vs aqueous-phase reactions of (•)OH with many atmospheric components. Moreover, considering the fact that people spend so much more time in dwellings than outside, the impact of the reactivity of indoor hydroxyl radicals on health and well-being is another emerging research topic of great concern.

Temperature-dependent rate constants for hydroxyl radical reactions with organic compounds in aqueous solutions

The OH radical is the most important oxidant in both the tropospheric gas and aqueous phase. Its main sink processes in clouds appear to be reactions with organics but due to the lack of appropriate kinetic data current cloud chemistry models consider only reactions with C1 and C2 compounds. Therefore, in this study temperature dependent rate constants for the reactions of the OH radical with organic compounds (≥C2) were determined. These investigations were performed by competition kinetics (reference substance: SCN−). Initially the experimental system was checked reinvestigating kinetic data for OH reactions with formate (R-1) and tert-butanol (R-2) available from literature. For the reactions (R-1) and (R-2) the following results were obtained: k1(298 K)=(2.4±0.4)×109 M−1 s−1; A1=(7.9±0.7)×1010 M−1 s−1; EA,1=(9±5) kJ mol−1 and k2(298 K)=(5.0±0.6)×108 M−1 s−1; A2=(3.3±0.1)×1010 M−1 s−1; EA,2=(10±3) kJ mol−1 for formate and tert-butanol, respectively. Temperature dependent rate constants for the reactions of OH with ethanol (k3(298 K)=(2.1±0.1)×109 M−1 s−1; A3=(1.0±0.1)×1011 M−1 s−1; EA,3=(10±5) kJ mol−1), 1-propanol (k4(298 K)=(3.2±0.2)×109 M−1 s−1; A4=(5.6±0.6)×1010 M−1 s−1; EA,4=(8±6) kJ mol−1), acetone (k5(298 K)=(2.1±0.6)×108 M−1 s−1; A5=(3.4±0.4)×1011 M−1 s−1; EA,5=(18±11) kJ mol−1) and methylglyoxal (k6(298 K)=(1.1±0.1)×109 M−1 s−1; A6=(2.9±0.3)×1011 M−1 s−1; EA,6=(13±6) kJ mol−1), Propionic acid: k7(298 K)=(3.2±0.5)×108 M−1 s−1; A7=(7.6±0.9)×1011 M−1 s−1; EA,7=(19±8) kJ mol−1; propionate: k8(298 K)=(7.2±0.4)×108 M−1 s−1; A8=(3.2±0.2)×1011 M−1 s−1; EA,8=(15±4) kJ mol−1; glyoxylic acid: k9(298 K)=(3.6±0.2)×108 M−1 s−1, A9=(8.1±0.4)×109 M−1 s−1, EA,9=(8±3) kJ mol−1, glyoxylate: k10(298 K)=(2.6±0.9)×109 M−1 s−1, A10=(6.0±0.4)×1015 M−1 s−1; EA,10=(36±8) kJ mol−1; pyruvic acid k11(298 K)=(1.2±0.4)×108 M−1 s−1; A11=(1.0±0.1)×1012 M−1 s−1; EA,11=(23±4) kJ mol−1; pyruvate: k12(298 K)=(7±2)×108 M−1 s−1; A12=(1.3±0.1)×1012 M−1 s−1; EA,12=(19±4) kJ mol−1; oxalate (monoanion): k13(298 K)=(1.9±0.6)×108 M−1 s−1; A13=(2.5±0.1)×1012 M−1 s−1; EA,13=(23±4) kJ mol−1; oxalate (dianion): k14(298 K)=(1.6±0.6)×108 M−1 s−1, A14=(4.6±0.5)×1014 M−1 s−1; EA,14=(36±10) kJ mol−1; malonate (monoanion): k15(298 K)=(6±1)×107 M−1 s−1, A15=(3.2±0.4)×109 M−1 s−1; EA,15=(11±5) kJ mol−1; succinic acid k18(298 K)=(1.1±0.1)×108 M−1 s−1, A18=(8±1)×109 M−1 s−1; EA,18=(11±6) kJ mol−1 and succinate (dianion): k19(298 K)=(5.0±0.5)×108 M−1 s−1, A19=(5.0±0.4)×1010 M−1 s−1; EA,19=(11±5) kJ mol−1 were determined.

Interactions of ozone with organic surface films in the presence of simulated sunlight: impact on wettability of aerosols

Heterogeneous reactions between organic films, taken as proxies for atmospheric aerosols, with ozone in presence of simulated sunlight and the photosensitizer 4-carboxybenzophenone (4-CB) were observed to alter surface properties as monitored by contact angle during the reaction. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR) was used in addition for product identification. Two types of model surfaces were systematically studied: 4-CB/4-phenoxyphenol and 4-CB/catechol. Solid organic films made of 4-CB/catechol were observed to become hydrophilic by simultaneous exposure to ozone and simulated sunlight, whereas organic films made of 4-CB/4-phenoxyphenol become hydrophobic under the same conditions. These changes in contact angle indicate that photo-induced aging processes involving ozone (such as oligomerisation) not necessarily favour increased hygroscopicity of organic aerosols in the atmosphere. The ratio between hydrophobic and hydrophilic functional groups should reflect the chemical property of organic films with respect to wettability phenomena. Contact angles and surface tensions of the exposed organic film made of 4-CB/4-phenoxyphenol were found to correspond to the hydrophobic/hydrophilic ratios obtained from the FTIR-ATR spectra.

The oxidative capacity of indoor atmospheres.

Sasho Gligorovski*,† and Charles J. Weschler*,‡,§ †Aix Marseille University, CNRS, Laboratoire de Chimie de l’Environnement (FRE 3416), (Case 29), 3 place Victor Hugo, F 13331 Marseille Cedex 3, France ‡Environmental and Occupational Health Sciences Institute, Rutgers University, 170 Frelinghuysen Road, Piscataway, New Jersey 08854, United States International Centre for Indoor Environment and Energy, Dept. of Civil Engineering, Technical University of Denmark, Nils Koppels Alle ́ 402, 2800, Lyngby, Denmark

Atmospheric Photosensitized Heterogeneous and Multiphase Reactions: From Outdoors to Indoors

This proposal involves direct photolysis processes occurring in the troposphere incorporating photochemical excitation and intermolecular energy transfer. The study of such processes could provide a better understanding of ·OH radical formation pathways in the atmosphere and in consequence, of a more accurate prediction of the oxidative capacity of the atmosphere. Compounds that readily absorb in the tropospheric actinic window (ionic organic complexes, PAHs, aromatic carbonyl compounds) acting as potential photosensitizers of atmospheric relevant processes are explored. The impact of hotosensitation on relevant systems which could act as powerful atmospheric reactors,that is, interface ocean-atmosphere, urban and forest surfaces and indoor air environments is also discussed.

The persistence of pesticides in atmospheric particulate phase: An emerging air quality issue.

The persistent organic pollutants (POPs) due to their physicochemical properties can be widely spread all over the globe; as such they represent a serious threat to both humans and wildlife. According to Stockholm convention out of 24 officially recognized POPs, 16 are pesticides. The atmospheric life times of pesticides, up to now were estimated based on their gas-phase reactivity. It has been only speculated that sorption to aerosol particles may increase significantly the half‐lives of pesticides in the atmosphere. The results presented here challenge the current view of the half-lives of pesticides in the lower boundary layer of the atmosphere and their impact on air quality and human health. We demonstrate that semivolatile pesticides which are mostly adsorbed on atmospheric aerosol particles are very persistent with respect to the highly reactive hydroxyl radicals (OH) that is the self-cleaning agent of the atmosphere. The half-lives in particulate phase of difenoconazole, tetraconazole, fipronil, oxadiazon, deltamethrin, cyprodinil, permethrin, and pendimethalin are in order of several days and even higher than one month, implying that these pesticides can be transported over long distances, reaching the remote regions all over the world; hence these pesticides shall be further evaluated prior to be confirmed as POPs.

Combustion Processes as a Source of High Levels of Indoor Hydroxyl Radicals through the Photolysis of Nitrous Acid

Hydroxyl radicals (OH) are known to control the oxidative capacity of the atmosphere but their influence on reactivity within indoor environments is believed to be of little importance. Atmospheric direct sources of OH include the photolysis of ozone and nitrous acid (HONO) and the ozonolysis of alkenes. It has been argued that the ultraviolet light fraction of the solar spectrum is largely attenuated within indoor environments, thus, limiting the extent of photolytic OH sources. Conversely, the ozonolysis of alkenes has been suggested as the main pathway of OH formation within indoor settings. According to this hypothesis the indoor OH radical concentrations span in the range of only 10(4) to 10(5) cm(-3). However, recent direct OH radical measurements within a school classroom yielded OH radical peak values at moderate light intensity measured at evenings of 1.8 × 10(6) cm(-3) that were attributed to the photolysis of HONO. In this work, we report results from chamber experiments irradiated with varying light intensities in order to mimic realistic indoor lighting conditions. The exhaust of a burning candle was introduced in the chamber as a typical indoor source causing a sharp peak of HONO, but also of nitrogen oxides (NOx). The photolysis of HONO yields peak OH concentration values, that for the range of indoors lightning conditions were estimated in the range 5.7 ×· 10(6) to 1.6 × 10(7) cm(-3). Excellent agreement exists between OH levels determined by a chemical clock and those calculated by a simple PSS model. These findings suggest that significant OH reactivity takes place at our dwellings and the consequences of this reactivity-that is, formation of secondary oxidants-ought to be studied hereafter.

Photolysis and Heterogeneous Reaction of Coniferyl Aldehyde Adsorbed on Silica Particles with Ozone

The pseudo-first-order loss of coniferyl aldehyde, adsorbed on silicon dioxide particles, upon heterogeneous ozonolysis was monitored at various ozone mixing ratios in the absence and presence of simulated sunlight. For the first time we investigated the effect of light on the heterogeneous ozonolysis of coniferyl aldehyde adsorbed on silica particles. We found that UV-VIS light (λ>300 nm) does not impact the degradation of coniferyl aldehyde by ozone but induces an additional, slow photolysis of the aldehyde with a photolytic rate constant of ~10(-5) s(-1). In both cases, that is, in presence and/or absence of light, the heterogeneous ozonation kinetics are well described by an immediate gas-surface reaction formalism with light-independent rate constants of k(2nd)=(7.2±0.9)×10(-19) cm(3) molec(-1) s(-1) and (7.6±1.7)×10(-19) cm(3) molec(-1) s(-1) in the absence and presence of light, respectively. Five oxidation products: glycolic acid, oxalic acid, vanillin, vanillic acid and 3,4-dihydroxybenzoic acid were identified and confirmed by their corresponding standards. Vanillin and vanillic acid absorb light in the region λ>300 nm and thus can further participate in the direct and indirect photolysis processes of atmospheric relevance. A reaction mechanism is proposed in order to elucidate the ozonolysis reaction and to explain the reaction products.

Characterisation and calibration of active sampling Solid Phase Microextraction applied to sensitive determination of gaseous carbonyls.

A characterisation of a system designed for active sampling of gaseous compounds with Solid Phase Microextraction (SPME) fibres is described. This form of sampling is useful to automate sampling while considerably reducing the sampling times. However, the efficiency of this form of sampling is also prone to be affected by certain undesirable effects such as fibre saturation, competition or displacement effects between analytes, to which particular attention should be paid especially at high flow rates. Yet, the effect of different parameters on the quantitivity of the results has not been evaluated. For this reason, in this study a careful characterisation of the influence of the parameters involved in active sampling SPME has been performed. A versatile experimental set-up has been designed to test the influence of air velocities and fluid regime on the quantitivity and reproducibility of the results. The mathematical model applied to the calculation of physical parameters at the sampling points takes into consideration the inherent characteristics of gases, distinctive from liquids and makes use of easily determined experimental variables as initial/boundary conditions to get the model started. The studies were carried out in the high-volume outdoor environmental chambers, EUPHORE. The sample subjected to study was a mixture of three aldehydes: pentanal, hexanal and heptanal and the determination methodology was O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine hydrochloride (PFBHA) on-fibre derivatisation. The present work proves that the determination procedure is quantitative and sensitive, independent from experimental conditions: temperature, relative humidity or ozone levels. With our methodology, the influence on adsorption of three inter-related variables, i.e., air velocity, flow rate and Reynolds numbers can be separated, since a change can be exerted in one of them while keeping the others constant.

Validation of Direct Analysis Real Time source/Time-of-Flight Mass Spectrometry for organophosphate quantitation on wafer surface.

Microelectronic wafers are exposed to airborne molecular contamination (AMC) during the fabrication process of microelectronic components. The organophosphate compounds belonging to the dopant group are one of the most harmful groups. Once adsorbed on the wafer surface these compounds hardly desorb and could diffuse in the bulk of the wafer and invert the wafer from p-type to n-type. The presence of these compounds on wafer surface could have electrical effect on the microelectronic components. For these reasons, it is of importance to control the amount of these compounds on the surface of the wafer. As a result, a fast quantitative and qualitative analytical method, nondestructive for the wafers, is needed to be able to adjust the process and avoid the loss of an important quantity of processed wafers due to the contamination by organophosphate compounds. Here we developed and validated an analytical method for the determination of organic compounds adsorbed on the surface of microelectronic wafers using the Direct Analysis in Real Time-Time of Flight-Mass Spectrometry (DART-ToF-MS) system. Specifically, the developed methodology concerns the organophosphate group.