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In this work, laboratory chamber experiments of gas-phase methyl iodide photolysis in the presence of ozone at three relative humidity conditions were performed to study the formation and physico-chemical properties of iodine oxide particles. The obtained results revealed significant morphological changes of iodine oxide particles that were observed to depend on relative humidity. The formed iodine oxide particles under dry conditions were supposed to be agglomerates of fine hygroscopic crystals. On the other hand, a humid atmosphere was observed to favor the formation of isomeric, tetragonal and orthorhombic hygroscopic crystals potentially composed of HIO3 likely formed from progressive hydration of iodine oxide clusters. This process leads to a release of molecular iodine, I2, which may indicate a potential role of I2O4 in the particles' evolution processes. The obtained results on the iodine oxides' behavior are important to the nuclear power plant safety industry since many of the organic iodides that may be released during a major nuclear power-plant accident contain radioactive isotopes of iodine that are known to have lethal or toxic impacts on human health.

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Short chain volatile iodinated organic compounds (VIOCs) are of great importance in many fields that include atmospheric chemistry, agriculture, and environmental chemistry related to nuclear power plant safety. Proton-transfer-reaction mass spectrometry (PTR-MS) allows for fast, sensitive, and online quantification of VIOCs if the chemical ionization (CI) reaction rate coefficients are known. In this work, the theoretical CI rate coefficients for the reactions of hydronium ions (H3 O+ ) and oxygen ions (O 2 + ) with selected atmospherically important short chain VIOCs are determined. The neutral CH3 I, CH2 I2 , C2 H5 I, iso-C3 H7 I, n-C3 H7 I, n-C4 H9 I, 2-C4 H9 I, n-C5 H11 I, 2-C5 H11 I, and 3-C5 H11 I have been chosen because these compounds are of atmospheric and environmental importance in the field of safety of nuclear plant reactors. Theoretical ion-molecule collision rate coefficients were determined using the Su and Chesnavich theory based on parametrized trajectory calculations. The proton affinity, ionization energy, dipole moment, and polarizability values of the neutral molecules were determined from density functional theory and coupled-cluster calculations. The newly calculated rate constants facilitate the use of the CI mass spectrometry in the atmospheric quantification of selected VIOCs.

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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.

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Gaseous nitrogen dioxide (NO2) represents an oxidant that is present in relatively high concentrations in various indoor settings. Remarkably increased NO2 levels up to 1.5 ppm are associated with homes using gas stoves. The heterogeneous reactions of NO2 with adsorbed water on surfaces lead to the generation of nitrous acid (HONO). Here, we present a HONO source induced by heterogeneous reactions of NO2 with selected indoor paint surfaces in the presence of light (300 nm<λ<400 nm). We demonstrate that the formation of HONO is much more pronounced at elevated relative humidity. In the presence of light (5.5 W m(-2)), an increase of HONO production rate of up to 8.6·10(9) molecules cm(-2) s(-1) was observed at [NO2]=60 ppb and 50% relative humidity (RH). At higher light intensity of 10.6 (W m(-2)), the HONO production rate increased to 2.1·10(10) molecules cm(-2) s(-1). A high NO2 to HONO conversion yield of up to 84% was observed. This result strongly suggests that a light-driven process of indoor HONO production is operational. This work highlights the potential of paint surfaces to generate HONO within indoor environments by light-induced NO2 heterogeneous reactions.

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The heterogeneous ozonolysis of naphthalene adsorbed on XAD-4 resin was studied using an annular denuder technique. The experiments involved depositing a known quantity of naphthalene on the XAD-4 resin and then measuring the quantity of the solid naphthalene that reacted away under a constant flow of gaseous ozone (0.064 to 4.9 ppm) for a defined amount of time. All experiments were performed at room temperature (26 to 30 °C) and atmospheric pressure. The kinetic rate coefficient for the ozonolysis reaction of naphthalene adsorbed on XAD-4 resin is reported to be (10.1 ± 0.4) × 10(-19) cm(3) molecule(-1) s(-1) (error is 2σ, precision only). This value is five times greater than the currently recommended literature value for the homogeneous gas phase reaction of naphthalene with ozone. The obtained rate coefficient is used to evaluate reaction artifacts from field concentration measurements of naphthalene, acenaphthene, and phenanthrene. The observed uncertainties associated with field concentration measurements of naphthalene, acenaphthene, and phenanthrene are reported to be much higher than the uncertainties associated with the artifact reactions. Consequently, ozone reaction artifact appears to be negligible compared to the observed field measurement uncertainty results.

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A flash photolysis-resonance fluorescence (FP-RF) technique was employed to study the kinetics and mechanism of the reaction of OH radicals with p-cymene at temperatures between 297 and 413 K in helium buffer gas. FP-RF experiments involved time-resolved detection of OH radicals by RF following vacuum-UV flash photolysis of H2O-p-cymene-He and H2O-He mixtures. Biexponential functions were fitted to decays of OH radicals according to reversible addition of OH radicals to p-cymene to form a single adduct. A rate constant of (15.7 ± 1.1) × 10(-12) is obtained (in units of cm(3) s(-1)) at room temperature (298 K) for the sum of the addition and abstraction channels (k1a + k1b) according to this simplified model. The Arrhenius plot reveals the step function typical of other aromatics and can be described using the expressions: 2 × 10(-13) exp(+1300 K/T) at temperatures between 297 K and 324 K and 10(-11) exp(-250 K/T) at temperatures between 345 K and 413 K. After consideration of the abstraction channel an equilibrium constant of k1a/k-1a = 6 × 10(-26) exp(+9700 K/T) cm(3) is obtained at temperatures between 297 and 325 K and 2 × 10(-36) exp(+17,000 K/T) cm(3) at temperatures between 325 and 380 K.

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Flash photolysis (FP) coupled with resonance fluorescence (RF) was used to measure the absolute rate coefficients for the reactions of OH(X(2)Π) radicals with C(2)H(5)I (k(1)), n-C(3)H(7)I (k(2)), and iso-C(3)H(7)I (k(3)) at temperatures between 297 and 372 K in 188 Torr of He; this represents the first temperature-dependent kinetics studies for the title reactions. The experiments involved time-resolved RF detection of the OH (A(2)Σ(+) → X(2)Π transition at λ = 308 nm) radicals following FP of H(2)O/C(2)H(5)I/He, H(2)O/n-C(3)H(7)I/He, and H(2)O/iso-C(3)H(7)I/He mixtures. The OH(X(2)Π) radicals were produced by FP of H(2)O in vacuum-UV at wavelengths λ > 120 nm. Decays of OH radicals in the presence of C(2)H(5)I, n-C(3)H(7)I, and iso-C(3)H(7)I were observed to be exponential, and the decay rates were found to be linearly dependent on the C(2)H(5)I, n-C(3)H(7)I, and iso-C(3)H(7)I concentrations. The results are described by the following Arrhenius expressions (units of cm(3) molecule(-1) s(-1)): k(1)(297-372 K) = (5.55 ± 3.20) × 10(-12) exp[-(830 ± 90) K/T], k(2)(300-370 K) = (1.65 ± 0.90) × 10(-11) exp[-(780 ± 90) K/T] and k(3)(299-369 K) = (7.58 ± 3.70) × 10(-12) exp[-(530 ± 80) K/T]. Reported errors in E/R and in the pre-exponential factors are 2σ random errors, returned by the weighted (by 1/σ(2)) least-squares fits to the kinetic data. The implications of the reported kinetic results for understanding both atmospheric and nuclear safety interests of C(2)H(5)I, n-C(3)H(7)I, and iso-C(3)H(7)I are discussed.

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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.

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Flash photolysis (FP) coupled to resonance fluorescence (RF) was used to measure the absolute rate coefficients (k(1)) for the reaction of OH(X(2)Π) radicals with diiodomethane (CH(2)I(2)) over the temperature range 295-374 K. The experiments involved time-resolved RF detection of the OH (A(2)Σ(+)→X(2)Π transition at λ = 308 nm) following FP of the H(2)O/CH(2)I(2)/He mixtures. The OH(X(2)Π) radicals were produced by FP of H(2)O in the vacuum-UV at wavelengths λ > 120 nm. Decays of OH radicals in the presence of CH(2)I(2) are observed to be exponential, and the decay rates are found to be linearly dependent on the CH(2)I(2) concentration. The results are described by the Arrhenius expression k(1)(T) = (4.2 ± 0.5) × 10(-11) exp[-(670 ± 20)K/T] cm(3) molecule(-1) s(-1). The implications of the reported kinetic results for understanding the atmospheric chemistry of CH(2)I(2) are discussed.

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A laser flash photolysis-resonance fluorescence (LFP-RF) technique is employed to investigate the kinetics and mechanism of the reactions of O((1)D(2)) with HCN [reaction (1)] and CH(3)CN [reaction (2)] as a function of temperature over the range 193-430 K. The experiments involve time-resolved RF detection of O((3)P(J)) or H((2)S(1/2)) following LFP of O(3)/X/He mixtures (X=HCN or CH(3)CN), some of which also contain N(2), H(2), and/or NO(2). Measured rate coefficients for total removal of O((1)D(2)) by HCN and CH(3)CN are well-described by the following Arrhenius expressions (units are 10(-10) cm(3) molecule(-1) s(-1)): k(1)(T)=1.08exp(+105/T) and k(2)(T)=2.54exp(-24/T). Temperature-dependent product yields of O((3)P(J)), k(1a)/k(1) and k(2a)/k(2) are well-described by the following Arrhenius-type expressions: k(1a)/k(1)=0.150exp(+200/T) and k(2a)/k(2)=0.0269 exp(+137/T). The H((2)S(1/2)) yield from reaction (2) is found to be 0.16±0.03 independent of temperature (200-423 K). Large 298 K yields of H((2)S(1/2)), 0.68±0.12 produced per O((1)D(2)) destroyed by HCN, are observed for reaction (1). However, observed kinetics suggest that only about half of detected H((2)S(1/2)) is generated as a primary product of the O((1)D(2))+HCN reaction, with the remainder generated via a fast secondary reaction. The implications of the reported kinetic and mechanistic results for understanding the atmospheric chemistry of HCN and CH(3)CN are discussed.

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This work summarizes the results of a study of atmospheric wet and dry deposition fluxes of Deisopropyl-atrazine (DEA), Desethyl-atrazine (DET), Atrazine, Terbuthylazine, Alachlor, Metolachlor, Diflufenican, Fenoxaprop-p-ethyl, Iprodione, Isoproturon and Cymoxanil pesticides conducted in Strasbourg, France, from August 2000 through August 2001. The primary objective of this work was to calculate the total atmospheric pesticide deposition fluxes induced by atmospheric particles. To do this, a modified one-dimensional cloud water deposition model was used. All precipitation and deposition samples were collected at an urban forested park environment setting away from any direct point pesticide sources. The obtained deposition fluxes induced by atmospheric particles over a forested area showed that the dry deposition flux strongly contributes to the total deposition flux. The dry particle deposition fluxes are shown to contribute from 4% (DET) to 60% (cymoxanil) to the total deposition flux (wet+dry).

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The uptake coefficients of NO2 on aqueous solutions containing guaiacol, syringol and catechol were determined over the pH range from 1 to 13 using the wetted wall flowtube technique. The measured uptake coefficients were used to determine the rate coefficients for the reaction of the physically dissolved NO2 with the neutral and deprotonated forms of phenolic compounds listed above. These organic compounds are ubiquitous not only in biomass burning plumes but also in soils, where they form part of the building blocks of humic acids. The NO2 uptake kinetics on solutions containing guaiacol, syringol or catechol were observed to be strongly pH dependent with uptake coefficients increasing from below 10(-7), under acidic conditions, to more than 10(-5) at pH values above 10. This behaviour illustrates the difference of reactivity between the neutral phenolic species and the phenoxide ions. The corresponding second order rate coefficients were typically observed to increase from 10(5) M(-1) s(-1) for the neutral compounds to a minimum of 10(8) M(-1) s(-1) for the phenoxide ions.

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