Search

Terbuthylazine (TBA) is regarded as a reference compound for the heterogeneous photooxidation of semi-volatile organic compounds (SVOCs) initiated by OH radicals, and the reaction rate constant has been used to evaluate the atmospheric lifetime of other pesticides/SVOCs. However, experiments on different carrier aerosols using different apparatus derived distinct results, therefore discussions were raised upon whether TBA should be regarded as persistent organic compounds (POPs) or not. In this study, we applied the self-synthesized silica particles (Stober particles) as carrier aerosols, which could simulate the reactions on mineral particles in the atmosphere. We investigated the heterogeneous reaction of OH radicals with TBA, by exposing a sub-monolayer coating of TBA on the Stober particles, to simulate the degradation of TBA on spherical particles in ambient air. The rate constants for the reaction of OH with TBA adsorbed on Stober particles were determined to be 2.4 ± 0.3 (in units of 10–12 cm3 molecule−1 s−1) at 25 °C. Heterogeneous reaction were also performed at 6.5 °C and − 10 °C, the rate constants were 2.3 ± 0.2 and 1.4 ± 0.1 (in units of 10–12 cm3 molecule−1 s−1), respectively. The atmospheric half-lives of TBA on Stober particles were estimated to be 53, 56, and 92 h at 25 °C, 6.5 °C, and -10 °C, respectively (based on the simulation parameter obtained from the Eley–Rideal (ER) mechanism). We also fit the experimental data to the Langmuir–Hinshelwood (LH) mechanism and the half-lives become shorter (33, 45, and 61 h at 25 °C, 6.5 °C, and -10 °C, respectively). There is no evidence from observation data that show that TBA could be transported to the remote region. TBA cannot be defined as a persistent organic pollutants (POPs). Reactions in the atmosphere might be a combined mechanism of both ER and LH theories.

As a newcomer in atmospheric chemistry, I had the opportunity to get to know Paul Crutzen during a NATO workshop organized by Karl-Heinz Becker in March 1977 in the Dolomites, where Paul was eager ...

Polycyclic aromatic hydrocarbons (PAHs) are common atmospheric pollutants and known to cause adverse health effects. Nitrated PAHs (NPAHs) are formed in combustion activities and by nitration of PAHs in the atmosphere and may be equally or more toxic, but their spatial and temporal distribution in the atmosphere is not well characterized. Using the global EMAC model with atmospheric chemistry and surface compartments coupled, we investigate the formation, abundance, and fate of two secondarily formed NPAHs, 2-nitrofluoranthene (2-NFLT) and 2-nitropyrene (2-NPYR). The default reactivity scenario, the model with the simplest interpretation of parameters from the literature, tends to overestimate both absolute concentrations and NPAH/PAH ratios at observational sites. Sensitivity scenarios indicate that NO2-dependent NPAH formation leads to better agreement between measured and predicted NPAH concentrations and that photodegradation is the most important loss process of 2-NFLT and 2-NPYR. The highest concentrations of 2-NFLT and 2-NPYR are found in regions with strong PAH emissions, but because of continued secondary formation from the PAH precursors, these two NPAHs are predicted to be spread across the globe.

The reversible reaction of OH radicals with 1,2,4,5-tetramethylbenzene (1245-TeMB, durene) leads to adducts at the substituted (ipso) and unsubstituted (ortho) positions of the ring. By the use of flash photolysis for production and resonance fluorescence for detection of OH, the gas-phase reactions of O-2 with these adducts were investigated over the temperature range of 300-340 K in He at 200 mbar. The decay of OH, generated by pulsed vacuum-UV photolysis of H2O, was monitored under slow-flow conditions in the presence of 1245-TeMB and O-2 at concentrations of up to 19 X 10(12) CM-3 and 2 X 10(16) cm(-3), respectively. Triexponential OH decays resulted from the unimolecular decomposition of the two adducts, representing OH reservoirs with different stabilities. In the presence of O-2, additional adduct loss pathways exist, leading to faster OH consumption. Triexponential functions fitted to these decays were analyzed to obtain rate constants for the reactions of O-2 with both adducts. Rate constants in the range of (4-13) x 10(-15) and (0.3-3) x 10(-15) cm(3)s(-1) were obtained for the ortho and the ipso adducts, respectively, depending on temperature and assumptions regarding details of the underlying mechanism of adduct isomer formation and isomerization. At O-2 concentrations exceeding about 1 x 10(16) cm(-3), deviations from a linear dependence of the adduct loss rates on the O-2 concentration indicate an even more complex mechanism. The validity of the rate constants is therefore confined to O-2 concentrations below 1 X 10(16) cm(-3). The adduct + O-2 rate constants for 1245-TeMB are greater than the corresponding previously obtained rate constants for benzene, toluene, and p- and m-xylene but smaller than those for hexamethylbenzene. The results are discussed in terms of the current knowledge about the mechanism of OH-induced degradation of aromatic compounds in the presence of O-2.

Terbuthylazine (TBA) is a widely used herbicide, and its heterogeneous reaction with OH radicals is important for assessing its potential to undergo atmospheric long-range transport and to affect the environment and public health. The apparent reaction rate coefficients obtained in different experimental investigations, however, vary by orders of magnitude depending on the applied experimental techniques and conditions. In this study, we used a kinetic multilayer model of aerosol chemistry with reversible surface adsorption and bulk diffusion (KM-SUB) in combination with a Monte Carlo genetic algorithm to simulate the measured decay rates of TBA. Two experimental data sets available from different studies can be described with a consistent set of kinetic parameters resolving the interplay of chemical reaction, mass transport, and shielding effects. Our study suggests that mass transport and shielding effects can substantially extend the atmospheric lifetime of reactive pesticides from a few days to weeks, with strong implications for long-range transport and potential health effects of these substances.

Polycyclic aromatic hydrocarbons (PAHs) and some of their nitrated derivatives, NPAHs, are seemingly ubiquitous in the atmospheric environment. Atmospheric lifetimes may nevertheless vary within a wide range, and be as short as a few hours. The sources and sinks of NPAH in the atmosphere are not well understood. With a Lagrangian field experiment and modeling, we studied the conversion of the semivolatile PAHs fluoranthene and pyrene into the 2-nitro derivatives 2-nitrofluoranthene and 2-nitropyrene in a cloud-free marine atmosphere on the time scale of hours to 1 day between a coastal and an island site. Chemistry and transport during several episodes was simulated by a Lagrangian box model i.e., a box model coupled to a Lagrangian particle dispersion model, FLEXPART-WRF. It is found that the chemical kinetic data do capture photochemical degradation of the 4-ring PAHs under ambient conditions on the time scale of hours to 1 day, while the production of the corresponding NPAH, which sustained 2-nitrofluoranthene/fluoranthene and 2-nitropyrene/pyrene yields of (3.7 ± 0.2) and (1.5 ± 0.1)%, respectively, is by far underestimated. Predicted levels of NPAH come close to observed ones, when kinetic data describing the reactivity of the OH-adduct were explored by means of theoretically based estimates. Predictions are also underestimated by 1-2 orders of magnitude, when NPAH/PAH yields reported from laboratory experiments conducted under high NOx conditions are adopted for the simulations. It is concluded that NPAH sources effective under low NOx conditions, are largely underestimated., Grant Agency of the Czech Republic (P503 16-115375); Izmir Institute of Technology Research Fund (2013IYTE-14); Max Planck Society; European Union (262254); Ministry of Education, Youth & Sports - Czech Republic (LM2015051/CZ.02.1.01/0.0/0.0/16_013/0001761)

The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe2O3) aerosol particles (mainly hematite, specific surface ~150 m2 g−1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe2O3 at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L−1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8 × 1021 atoms cm−2 h−1, respectively. In a further series of experiments, the pure Fe2O3 aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8 × 1020 Cl atoms cm−2 h−1 (at ~4 ppb HCl) to 5 × 1022 Cl atoms cm−2 h−1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe2O3 experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl.

Chloromethane (CH3Cl) is the most important natural input of reactive chlorine to the stratosphere, contributing about 16 % to stratospheric ozone depletion. Due to the phase-out of anthropogenic emissions of chlorofluorocarbons, CH3Cl will largely control future levels of stratospheric chlorine. The tropical rainforest is commonly assumed to be the strongest single CH3Cl source, contributing over half of the global annual emissions of about 4000 to 5000 Gg (1 Gg = 109 g). This source shows a characteristic carbon isotope fingerprint, making isotopic investigations a promising tool for improving its atmospheric budget. Applying carbon isotopes to better constrain the atmospheric budget of CH3Cl requires sound information on the kinetic isotope effects for the main sink processes: the reaction with OH and Cl in the troposphere. We conducted photochemical CH3Cl degradation experiments in a 3500 dm3 smog chamber to determine the carbon isotope effect (ε=k13C/k12C-1) for the reaction of CH3Cl with OH and Cl. For the reaction of CH3Cl with OH, we determined an ε value of (-11.2±0.8) ‰ (n=3) and for the reaction with Cl we found an ε value of (-10.2±0.5) ‰ (n=1), which is 5 to 6 times smaller than previously reported. Our smaller isotope effects are strongly supported by the lack of any significant seasonal covariation in previously reported tropospheric δ13C(CH3Cl) values with the OH-driven seasonal cycle in tropospheric mixing ratios. Applying these new values for the carbon isotope effect to the global CH3Cl budget using a simple two hemispheric box model, we derive a tropical rainforest CH3Cl source of (670±200) Gg a−1, which is considerably smaller than previous estimates. A revision of previous bottom-up estimates, using above-ground biomass instead of rainforest area, strongly supports this lower estimate. Finally, our results suggest a large unknown CH3Cl source of (1530±200) Gg a−1.

Chloromethane (CH3Cl) is an important provider of chlorine to the stratosphere but yet lacks detailed knowledge of its budget. Stable isotope analysis is potentially a powerful tool to constrain CH3Cl flux estimates. The largest degree of isotope fractionation is expected to occur for deuterium in CH3Cl in the hydrogen abstraction reactions with its main sink reactant tropospheric OH and its minor sink reactant Cl atoms. We determined the isotope fractionation by stable hydrogen isotope analysis of the fraction of CH3Cl remaining after reaction with hydroxyl and chlorine radicals in a 3.5 m3 Teflon smog-chamber at 293 ± 1 K. We measured the increasing stable hydrogen isotope values of the unreacted CH3Cl using compound specific thermal conversion isotope ratio mass spectrometry. The isotope fractionations of CH3Cl for the reactions with hydroxyl and chlorine radicals were found to be −242 ± 7 mUr (or ‰) and −280 ± 11 mUr, respectively. For comparison, we performed similar experiments using methane (CH4) as the target compound with OH and obtained a fractionation constant of −205 ± 6 mUr which is in good agreement with values previously reported. The observed large kinetic isotope effects are helpful when employing isotopic analyses of CH3Cl in the atmosphere to improve our knowledge of its atmospheric budget.

The chemistry of the troposphere and specifically the global tropospheric ozone budget is affected by reactive halogen species such as bromine monoxide (BrO) or chlorine monoxide (ClO). Especially BrO plays an important role in the processes of ozone destruction, disturbance of NOx and HOx chemistry, oxidation of dimethyl sulfide (DMS), and the deposition of elementary mercury. In the troposphere BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer. For a better understanding of these processes, field measurements as well as reaction chamber studies are performed. In both cases instruments with high spatial resolution and high sensitivity are necessary. A Cavity-Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument with an open path measurement cell was designed and applied. For the first time, a CE-DOAS instrument is presented using an UV LED in the 325–365 nm wavelength range. In laboratory studies, BrO as well as HONO, HCHO, O3, and O4 could be reliably determined at detection limits of 20 ppt for BrO, 9.1 ppb for HCHO, 970 ppt for HONO, and 91 ppb for O3, for five minutes integration time. The best detection limits were achieved for BrO (11 ppt), HCHO (5.1 ppb), HONO (490 ppt), and O3 (59 ppb) for integration times of 81 minutes or less. Comparison with established White system (WS) DOAS and O3 monitor measurements demonstrate the reliability of the instrument.

A flash photolysis-resonance fluorescence technique was used to investigate the kinetics of the OH(X-2 Pi) radical and O(P-3) atom-initiated reactions with CHI3 and the kinetics of the O(P-3) atom-initiated reaction with C2H5I. The reactions of the O(P-3) atom with CHI3 and C2H5I were studied over the temperature range of 296 to 373 K in 14 Torr of helium, and the reaction of the OH (X-2 Pi) radical with CHI3 was studied at T = 298 K in 186 Torr of helium. The experiments involved time-resolved resonance fluorescence detection of OH (A(2)Sigma(+) -> X-2 Pi transition at lambda = 308 nm) and of O(P-3) (lambda = 130.2, 130.5, and 130.6 nm) following flash photolysis of the H2O/He, H2O/CHI3/He, O-3/He, and O-3/C2H5I/He mixtures. A xenon vacuum UV (VUV) flash lamp (lambda > 120 nm) served as a photolysis light source. The OH radicals were produced by the VUV flash photolysis of water, and the O(P-3) atoms were produced by the VUV flash photolysis of ozone. Decays of OH radicals and O(P-3) atoms in the presence of CHI3 and C2H5I were observed to be exponential, and the decay rates were found to be linearly dependent on the CHI3 and C2H5I concentrations. Measured rate coefficients for the reaction of O(P-3) atoms with CHI3 and C2H5I are described by the following Arrhenius expressions (units are cm(3) s(-1)): k(O+C2H5I)(T) = (17.2 +/- 7.4) x 10(-12) exp[-(190 +/- 140)K/T] and k(O+CHI3)(T) = (1.80 +/- 2.70) x 10(-12) exp[-(440 +/- 500)K/T]; the 298 K rate coefficient for the reaction of the OH radical with CHI3 is k(OH+CHI3)(298 K) = (1.65 +/- 0.06) x 10(-11) cm(3) s(-1). The listed uncertainty values of the Arrhenius parameters are 2 sigma-standard errors of the calculated slopes by linear regression. (C) 2014 Wiley Periodicals, Inc.

International audience; 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 < lambda < 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.

A new method for the analysis of trace gases from fluid inclusions of minerals has been developed. The purge and trap GC-MS system is based on the system described by Nolting et al. (1988) and was optimized for the analyses of halogenated volatile organic compounds (VOCs) having boiling points as low as -128. °C (carbon tetrafluoride).The sample preconcentration cold trap consists of a U-shaped glass lined steel tube (GLT™), that is immersed into a small liquid nitrogen Dewar vessel for cooling. A rapid desorption step heats up the preconcentration tube in

Reactive halogen species (RHS), such as Cl, Br, or BrO, can have significant influence on chemical processes in the troposphere, including the destruction of ozone, change in the chemical balance of OH and HO2, and increased deposition of toxic compounds (like mercury), with potential consequences for the global climate. Previous studies have shown that salt lakes can provide a significant source for gaseous RHS. Environmental conditions, such as salt composition, relative humidity (RH), pH, and temperature (T), might have a strong influence on reactive bromine levels. In our laboratory experiments, NaCl salt containing 0.33% NaBr by weight was exposed to simulated sunlight in a Teflon smog chamber under various conditions of RH and ozone concentrations. BrO levels were observed by a differential optical absorption spectrometer in combination with a multireflection cell (White cell). The concentrations of OH and Cl radicals were quantified by the radical clock method. We present the first direct observation of BrO from the “bromine explosion” (autocatalytic release of reactive bromine from salt surfaces—key to ozone destruction) in the laboratory above a simulated salt pan. The maximum BrO mixing ratio of 6419 ± 71 ppt at 60% RH was observed to be one order of magnitude higher than at 37% RH and 2% RH. The release of RHS from the salt pan is possibly controlled by the thickness of the quasi-liquid layer, covering the reactive surface of the halide crystals, as the layer thickness strongly depends on RH. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 312–326, 2012

During the DOMINO (Diel Oxidant Mechanism In relation to Nitrogen Oxides) campaign in southwest Spain we measured simultaneously all quantities necessary to calculate a photostationary state for HONO in the gas phase. These quantities comprise the concentrations of OH, NO, and HONO and the photolysis frequency of NO2, j(NO2) as a proxy for j(HONO). This allowed us to calculate values of the unknown HONO daytime source. This unknown HONO source, normalized by NO2 mixing ratios and expressed as a conversion frequency (% h−1), showed a clear dependence on j(NO2) with values up to 43% h−1 at noon. We compared our unknown HONO source with values calculated from the measured field data for two recently proposed processes, the light-induced NO2 conversion on soot surfaces and the reaction of electronically excited NO2* with water vapour, with the result that these two reactions normally contributed less than 10% (

We have combined chemical and micrometeorological measurements to investigate the formation and distribution of HONO throughout a forest canopy. HONO was measured simultaneously at two heights, close to the forest floor and just above canopy. The turbulent exchange between the forest and the atmosphere above was studied using vertical profiles of eddy covariance measurements of wind velocity, sonic temperature, water vapour and CO2. HONO mixing ratios at both heights showed typical diel cycles with low daytime values (~80 ppt) and high nighttime values (up to 500 ppt), but were influenced by various sources and sinks leading to mixing ratio differences (above canopy minus below) of up to +240 ppt at nighttime. In the late afternoon and early night mixing ratios increased at higher rates near the forest floor, indicating a possible ground source. Due to the simultaneous decoupling of the forest from the air layer above the canopy, mixing ratio differences reached about −170 ppt. From the late night until the early morning mixing ratios above the forest were typically higher than close to the forest floor. For some cases, this could be attributed to advection above the forest, which only partly penetrated the canopy. Measured photolysis frequencies above and below the forest canopy differed by a factor of 10–25 resulting in HONO lifetimes of about 10 min above and 100–250 min below the canopy at noontime. However, these differences of the main daytime HONO sink were not evident in the mixing ratio differences, which were close to zero during the morning hours. Effective turbulent exchange due to a complete coupling of the forest to the air layer above the canopy in the morning has offset the differences caused by the daytime photolytic sink and added to the interplay between different HONO production and loss processes.

Secondary organic aerosol (SOA) was produced from the aromatic precursors catechol and guaiacol by reaction with ozone in the presence and absence of simulated sunlight and humidity and investigated for its properties as a proxy for HUmic-LIke Substances (HULIS). Beside a small particle size, a relatively low molecular weight and typical optical features in the UV/VIS spectral range, HULIS contain a typical aromatic and/or olefinic chemical structure and highly oxidized functional groups within a high chemical diversity. Various methods were used to characterize the secondary organic aerosols obtained: Fourier transform infrared spectroscopy (FTIR) demonstrated the formation of several carbonyl containing functional groups as well as structural and functional differences between aerosols formed at different environmental conditions. UV/VIS spectroscopy of filter samples showed that the particulate matter absorbs far into the visible range up to more than 500 nm. Ultrahigh resolved mass spectroscopy (ICR-FT/MS) determined O/C-ratios between 0.3 and 1 and observed m/z ratios between 200 and 450 to be most abundant. Temperature-programmed-pyrolysis mass spectroscopy (TPP-MS) identified carboxylic acids and lactones/esters as major functional groups. Particle sizing using a condensation-nucleus-counter and differential-mobility-particle-sizer (CNC/DMPS) monitored the formation of small particles during the SOA formation process. Particle imaging, using field-emission-gun scanning electron microscopy (FEG-SEM), showed spherical particles, forming clusters and chains. We conclude that catechol and guaiacol are appropriate precursors for studies of the processing of aromatic SOA with atmospheric HULIS properties on the laboratory scale.

UV absorption cross-sections of six vinyl ethers (ethyl vinyl ether, 1,4-butanediol divinyl ether, isobutyl vinyl ether, cyclohexyl vinyl ether, 4-hydroxybutylvinyl ether and diethyleneglycol divinyl ether) have been determined in the gas phase between 190 and 230 nm at 303 ± 2 K and pressures up to the corresponding saturation vapor pressures. The main band maxima of the vinyl ethers are below 200 nm with values under 8 × 10−17 cm2 molecule−1. The absorption vanishes above 225 nm with values of σ smaller than 1 × 10−21 cm2 molecule−1. Weak, overlaying vibrational progressions with spacings of 1400 cm−1 are observed for the alkyl vinyl ethers and are less pronounced for vinyl ethers with an extra O atom. Shifts of the positions and intensities are discussed on the basis of the differences in the chemical structure of this series.

A quantitative analysis of the technical octabromo diphenylether mixture DE-79™ is performed by 1 H NMR, avoiding any separation technique. The mass fractions are 36% BDE183, 19% BDE197, 13.1% BDE207, 9.1% BDE196, 7.3% BDE153, 6.2% BDE203, 2.2% BDE180, 1.6% BDE171, 1.2% BDE154 and 0.7% BDE206, considering an additional mass fraction of 1.3% BDE209 determined by HPLC analysis with a diode array detector (DAD). HPLC chromatograms of the BDEs in commercial decaBDE, octaBDE DE-79™ and pentaBDE DE-71™ and UV spectra of the components of DE-79™ are presented. The photolysis of the octaBDE mixture DE-79™, dissolved in tetrahydrofuran, by simulated sunlight is monitored by HPLC-DAD and observed to proceed mainly via debromination. Polybrominated dibenzofurans are identified from their UV spectra as significant intermediates.

Atmospharische Aerosolpartikel sind keine chemisch inerten Teilchen, deren Bildungsmechanismen, Verweildauer oder Funktion in der Atmosphare lediglich von mechanischen oder physikalischen Prozessen abhangen. Sowohl bei der Bildung von Aerosolpartikeln als auch im Verlauf ihres Verbleibs in der Atmosphare spielen chemische Reaktionen eine wesentliche Rolle. Chemische Reaktionen laufen an der Oberflache und im Inneren von Aerosolpartikeln ab und konnen sowohl die atmospharische Gasphasenchemie beeinflussen, z.B. indem sie sowohl als Reaktionsmedium fur ansonsten langsam verlaufende Gasphasenreaktionen dienen, als auch die Eigenschaften der Partikel, beispielsweise ihre Funktion als Kondensationskerne bei der Wolkenbildung. Atmospheric aerosols are not chemical inert airborne particles whose formation mechanisms, residence time or function in the atmosphere just dependent from mechanical or physical processes. In the course of the aerosol formation process as well as during their stay and transport in the atmosphere chemical reactions play an essential role. Chemical reactions take place at the surface and within aerosol particles and can not only influence gas phase chemistry, e.g. by serving as a reaction media for otherwise slow gas phase reactions, they can also alter the physico-chemical properties of the particles, e.g. their function as cloud condensation nuclei. This review summaries the current knowledge about the chemistry of aerosol, focusing on secondary aerosol formation processes and heterogeneous chemistry of sea salt, dust and soot particles.

Consecutive reactions of adducts, resulting from OH radicals and aromatics, with the tropospheric scavenger molecules O2, NO and NO2 have been studied for benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline by observing decays of OH at temperatures where the thermal back-decomposition to OH is faster than 3 s−1, typically between 300 and 340 K. The experimental technique was resonance fluorescence with flash photolysis of water as source of OH. Biexponential decays were observed in the presence of either O2 or NO, and triexponential decays were obtained in the presence of NO2. The kinetic analysis was performed by fitting the relevant rate constants of the reaction mechanism to whole sets of decays obtained at various concentrations of aromatic and scavenger. In the case of hexamethylbenzene, the biexponential decays suggest the existence of the ipso-adduct, and the slightly higher necessary temperatures show that it is even more stable. In addition, smog chamber experiments at O2 concentrations from atmospheric composition down to well below 100 ppm have been carried out for benzene, toluene and p-xylene. The drop of the effective rate constant of removal by OH occurs at reasonable O2 levels, given the FP/RF results. Comparison of the adduct reactivities shows for all aromatics of this study that the reaction with O2 predominates over that with NO2 under all tropospheric conditions, and that a reaction with NO may only occur after the reaction with O2.

Environmental context Secondary organic aerosols together with sea-salt aerosols are a major contribution to global aerosols and influence the release of reactive halogens, which affect air quality and human health. In this study, the loss of reactive halogen species from simulated salt aerosols due to three different types of secondary organic aerosols was quantified in chamber experiments and investigated with the help of a numerical model. The loss rate can be included into chemistry models of the atmosphere and help to quantify the halogen budget in nature. Abstract The interaction between secondary organic aerosols (SOAs) and reactive bromine species (e.g. BrO, Br2, HOBr) coexisting in the environment is not well understood and not included in current chemistry models. The present study quantifies the quenching of bromine release from an artificial salt aerosol caused by SOAs from ozonolysis of three precursors (α-pinene, catechol or guaiacol) in a Teflon smog chamber and incorporates it into a chemical box model. The model simulations perform very well for a blank experiment without SOA precursor, capturing BrO formation, as detected by differential optical absorption spectrometry. A first-order BrO loss rate of 0.001s–1 on the surface of SOA represents the overall effective Brx (total inorganic bromine) loss included in the model. Generally, the model agrees with the maximum BrO mixing ratio in time and magnitude, with some disagreements in the exact shape. Formation of reactive OClO was observed in the presence of organics but could not be reproduced by the model. According to current knowledge, most inorganic chlorine would be in the form of HCl in the presence of organics, as predicted by the model. In order to reproduce the net effects of the presence of SOA, the effective uptake coefficients of reactive bromine on the SOA surface are estimated to be 0.01, 0.01 and 0.004 for α-pinene, catechol and guaiacol respectively. The uptake coefficient can now be incorporated into box models and even global models, where sinks for bromine species are thought to be inadequately represented.

International audience; Hydroxyl radicals (OH) are known to control the oxidative capacity of the atmosphere but then 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 104 to 108 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 x 106 cm(-3) that Were attributed to the photolysis of HONa 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 X 10(6) to 1.6 x 107 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.

The reaction of OH radicals with a series of methylated benzenes was studied in a temperature range 300-350 K using a flash-photolysis resonance fluorescence technique. Reversible OH additions led to complex OH decays dependent on the number of distinguishable adducts. Except for hexamethylbenzene, triexponential OH decay curves were obtained, consistent with formation of at least two adduct species. For three compounds that can strictly form two adduct isomers for symmetry reasons (1,4-dimethyl-, 1,3,5-trimethyl-, and 1,2,4,5-tetramethylbenzene) with OH bound ortho or ipso with respect to the methyl groups, OH decay curves were analysed in terms of a reaction mechanism in which the two adducts can be formed directly by OH addition or indirectly by isomerization. In all cases one adduct (add1) is dominating the decomposition back to OH. The other (add2) is more elusive and only detectable at elevated temperatures, similar to the single OH adduct of hexamethylbenzene. Two limiting cases of the general reaction mechanism could be examined quantitatively: reversible formation of add2 exclusively in the OH reaction or by isomerization of add1. Total OH rate constants, adduct loss rate constants and products of forward and reverse rate constants of reversible reactions were determined. From these quantities, adduct yields, equilibrium constants, as well as reaction enthalpies and entropies were derived for the three aromatics. Adduct yields strongly depend on the selected reaction model but generally formation of add1 predominates. For both models equilibrium constants of OH reactions lie between those of OH + benzene from the literature and those obtained for OH + hexamethylbenzene. The corresponding reaction enthalpies of add1 and add2 formations are in a range -87 ± 20 kJ mol(-1), less exothermic than for hexamethylbenzene (-101 kJ mol(-1)). Reaction enthalpies of possible add1 → add2 isomerizations are comparatively small. Because results for 1,3,5-trimethylbenzene are partly inconsistent with a direct formation of add2, we promote the existence of isomerization reactions. Moreover, based on available theoretical work in the literature, add1 and add2 are tentatively identified as ortho and ipso adducts, respectively. Total OH rate constants were obtained for all title compounds. They can be described by Arrhenius equations: kOH = A × exp(-B/T). The parameters ln(A/(cm(3) s(-1))) = -25.6 ± 0.3, -25.3 ± 0.6, -27.3 ± 0.3, -24.6 ± 0.3, -26.2 ± 0.4, -26.2 ± 0.4 and -24.5 ± 0.2, and B/K = -160 ± 90, -550 ± 180, -1120 ± 90, -330 ± 100, -820 ± 100, -980 ± 130, and -570 ± 40 were determined for 1,4-dimethyl-, 1,3,5-trimethyl-, 1,2,4,5-, 1,2,3,5- and 1,2,3,4-tetramethyl-, pentamethyl-, and hexamethylbenzene.

Nanoparticles of simulated sea spray were investigated in the presence of ozone in a Teflon chamber, where photochemical experiments on droplets (above 76% relative humidity) with Br enrichments up to a factor of 6 released OH radicals, (2-6) x 10 6 cm -3 , atomic Cl (2-10) × 10 4 cm -3 and atomic Br up to 3 x 10 8 cm -3 . 3. Sub-micrometer sized agglomerates of nano-sized fused silica and alumina particles in a glass chamber served for degradation experiments of the semivolatile compound octadecyl vinyl ether (ODVE). Adsorbates of ODVE at submonolayer thickness on such substrates were observed to hydrolyse rapidly to form 1-octadecanol (within a few hours). Treating the particles with NaOH before coating diminished hydrolysis, and exposing an aerosol of Alumina C (Degussa), coated with ODVE, to gaseous OH radicals in a glass chamber delivered rate constants for the consumption of ODVE and its hydrolysis product, 1-octadecanol, which need further interpretation in terms of volatilisation and surface properties. This study reports first aerosol smog chamber experiments on such nanoparticles in a new facility that can be cooled to -28 °C.

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.

International audience; Nitrous acid (HONO) can be generated in various indoor environments directly during combustion processes or indirectly via heterogeneous NO2 reactions with water adsorbed layers on diverse surfaces. Indoors not only the concentrations of NO2 are higher but the surface to volume (Sly) ratios are larger and therefore the potential of HONO production is significantly elevated compared to outdoors. It has been claimed that the UV solar light is largely attenuated indoors. Here, we show that solar light (lambda > 340 nm) penetrates indoors and can influence the heterogeneous reactions of gas-phase NO2 with various household surfaces. The NO2 to HONO conversion mediated by light on surfaces covered with domestic chemicals has been determined at atmospherically relevant conditions i.e. 50 ppb NO2 and 50% RH. The formation rates of HONO were enhanced in presence of light for all the studied surfaces and are determined in the following order: 1.3.10(9) molecules cm(-2) s(-1) for borosilicate glass, 1.7.10(9) molecules cm(-2) s(-1) for bathroom cleaner, 1.0.10(10) molecules cm(-2) s(-1) on alkaline detergent (floor cleaner), 1.3.10(19) molecules cm(-2) s(-1) for white wall paint and 2.7.10(19) molecules cm(-2) s(-1) for lacquer. These results highlight the potential of household chemicals, used for cleaning purposes to generate HONO indoors through light-enhanced NO2 heterogeneous reactions. The results obtained have been applied to predict the timely evolution of HONO in a real indoor environment using a dynamic mass balance model. A steady state mixing ratio of HONO has been estimated at 1.6 ppb assuming a contribution from glass, paint and lacquer and considering the photolysis of HONO as the most important loss process. (C) 2014 Elsevier Ltd. All rights reserved.

The photochemistry of halides in sea spray aerosol, on salt pans, and on other salty surfaces leads to a formation of reactive halogen species. We investigated the photochemical formation of atomic chlorine (Cl) and bromine (Br) in the gas phase in the presence of laboratory-modeled salt pans consisting of sodium chloride doped with iron(III) chloride hexahydrate (0.5 and 2 wt %). The samples were spread on a Teflon sheet and exposed to simulated sunlight in a Teflon smog chamber in purified, humidified air in the presence of a test mixture of hydrocarbons at the ppb level to determine Cl, Br, and OH formation by the radical clock method. Driven by the photolytic reduction of Fe(III) to Fe(II), the production rates of the Fe(III)-doped NaCl salt samples (up to10(7) atoms cm(-3) s(-1)) exceeded the release of Cl above a pure NaCl sample by more than an order of magnitude in an initially O3-free environment at low NOX. In bromide-doped samples (0.5 wt % NaBr), a part of the Cl release was replaced by Br when Fe(III) was present. Additions of sodium sulfate, sodium oxalate, oxalic acid, and catechol to NaCl/FeCl3 samples were found to restrain the activation of chloride.

A flash photolysis-resonance fluorescence (FP-RF) system was used to study the p-cymene (PC) + OH reaction at temperatures between 299 and 349 K in helium. Triexponential functions were fitted to groups of observed OH decay curves according to a model considering a reversible addition to form two adducts as thermolabile reservoirs of OH. Compared to Part 1 of this paper, consideration of a second adduct strongly improved the fits to our measurements, and the rate constants for the major pathways were optimized between 299 and 349 K. The Arrhenius expression for the rate constant of the sum of OH addition and H-atom abstraction pathways was found to be kOH = 1.9 × 10(-12) exp[(610 ± 210) K/T] cm(3) s(-1). Rate constants of unimolecular decomposition reactions of the adducts were similar to other aromatic compounds with the following Arrhenius expressions: 1 × 10(12) exp[(-7600 ± 800) K/T] s(-1) for adduct 1 and 4 × 10(11) exp[(-8000 ± 300) K/T] s(-1) for adduct 2. Adduct yields increased and decreased with temperature for adduct 1 and 2, respectively, but were similar (∼0.4) around room temperature. Equilibrium constants yielded values for reaction enthalpies and entropies of adduct formations. While for one adduct reasonable agreement was obtained with theoretical predictions, there were significant deviations for the other adduct. This indicates the presence of more than two adduct isomers that were not accounted for in the reaction model. Quantum chemical calculations (DFT M06-2X/6-31G(d,p)) and RRKM kinetics were employed with the aim of clarifying the mechanism of the OH addition to PC. These calculations show that formation of adducts with OH in ortho positions to the isopropyl and methyl substituents is predominant (55% and 24%) to those with OH in ipso positions (21% and 3%). A large fraction (90%) of the ipso-C3H7 adduct is predicted to react by dealkylation forming p-cresol (in the absence of oxygen) and isopropyl radicals. These theoretical results agree well with the interpretation of the experimental results showing that the two ortho adducts (which appeared as OH reservoirs in the experiment) have been observed.

Rockström et al. (2009a, 2009b) have warned that humanity must reduce anthropogenic impacts defined by nine planetary boundaries if “unacceptable global change” is to be avoided. Chemical pollution was identified as one of those boundaries for which continued impacts could erode the resilience of ecosystems and humanity. The central concept of the planetary boundary (or boundaries) for chemical pollution (PBCP or PBCPs) is that the Earth has a finite assimilative capacity for chemical pollution, which includes persistent, as well as readily degradable chemicals released at local to regional scales, which in aggregate threaten ecosystem and human viability. The PBCP allows humanity to explicitly address the increasingly global aspects of chemical pollution throughout a chemical's life cycle and the need for a global response of internationally coordinated control measures. We submit that sufficient evidence shows stresses on ecosystem and human health at local to global scales, suggesting that conditions are transgressing the safe operating space delimited by a PBCP. As such, current local to global pollution control measures are insufficient. However, while the PBCP is an important conceptual step forward, at this point single or multiple PBCPs are challenging to operationalize due to the extremely large number of commercial chemicals or mixtures of chemicals that cause myriad adverse effects to innumerable species and ecosystems, and the complex linkages between emissions, environmental concentrations, exposures and adverse effects. As well, the normative nature of a PBCP presents challenges of negotiating pollution limits amongst societal groups with differing viewpoints. Thus, a combination of approaches is recommended as follows: develop indicators of chemical pollution, for both control and response variables, that will aid in quantifying a PBCP(s) and gauging progress towards reducing chemical pollution; develop new technologies and technical and social approaches to mitigate global chemical pollution that emphasize a preventative approach; coordinate pollution control and sustainability efforts; and facilitate implementation of multiple (and potentially decentralized) control efforts involving scientists, civil society, government, non-governmental organizations and international bodies. Keywords: Planetary boundary, Chemical pollution, Chemical emissions, Stockholm Convention, Tipping point, Global threshold, Pollution controls, Ecosystem health protection, Human health protection, Chemical management

The reactivity of both isomers (Z and E) of pyrifenox (2′,4′-dichloro-2-(3-pyridyl)acetophenone (E,Z)O-methyloxime), adsorbed on quartz-aerosol as an inert carrier, against OH radicals from the gas-phase was investigated in a smog chamber (2400 l) at T=299 K and 50% rel. humidity. OH-radicals were produced in the dark using hydrazine/ozone and peroxynitric acid/NO and by photolysis using methyl nitrite, hydrogen peroxide, ozone and nitrogen dioxide as OH-precursors. OH-radical concentrations (< 105 < [OH]/cm−3 < 8 · 106) were determined from the simultaneous consumption of up to 6 reference compounds with well-known OH-rate constants. Using methyl nitrite, nitrogen dioxide and peroxynitric acid as OH-precursors the OH-rate constant at T=299 K for pyrifenox was found to be identical for both isomers: (kOH ± σ) = (1.8 ± 0.4)·10−11cm3·s−1 leading to half-lives of pyrifenox in the atmosphere of t12 = (0.45 – 0.9) days at typical mean, tropospheric OH-radical concentrations in the range of [OH] = (5 – 10) · 105 cm−3. Side reactions of HO2 or other radicals perturbed the degradation behaviour of pyrifenox in the presence of hydrazine/ozone and hydrogen peroxide and ozone under irradiation and were separated from OH. The rate constants for the reaction with gaseous hydrogen peroxide and ozone were determined, found to be low and negligible with respect to the degradation of pyrifenox in the environment: (kO3 ± σ) = (2 ± 1) · 10−19 cm3 s−1 and (kH2O2 ± σ) = (8 ± 8) · 10−20 cm3 s−1. Besides the reaction with OH-radicals a photo- isomerization Z ⇌ E was found. Within the error of experiments no irreversible loss of pyrifenox due to photolysis was found. A ketone (after reaction of OH at the CH2-group in pyrifenox) was tentatively assigned as the only product found.

The reaction of OH radicals with benzene and consecutive reactions of benzene–OH adducts with O2 were studied in the gas phase in N2–O2 mixtures at atmospheric pressure and room temperature. OH was produced by pulsed 248 nm photolysis of H2O2. Time-resolved detection of both OH and benzene–OH adducts was performed by continuous-wave (cw) UV-laser long-path absorption at around 308 nm. The reaction: OH+benzene→products [reaction (1)] was not affected by the presence of O2. Rate constants k1=(1.10±0.07)×10-12 cm3 s-1 and (1.06±0.07)×10-12 cm3 s-1 were obtained in N2 and O2, respectively. In N2 addition of NO2 did not change k1, from which an upper limit of 5% is derived for formation of H atoms in reaction (1). An absorption cross-section of σ(308 nm)=(5.8±1.5)×10-18 cm2 and a self-reaction rate constant of (3.4±1.7)×10-11 cm3 s-1 were determined for the benzene–OH adduct. Upper limits of 5×10-15 cm3 s-1, 1×10-14 cm3 s-1 and 5×10-14 cm3 s-1 were obtained for reactions of the adduct with benzene, H2O2 and NO, respectively. The adduct kinetics in the presence of O2 is consistent with the reversible formation of a peroxy radical: adduct+O2↔adduct–O2 [reaction (2a/-2a)]. An equilibrium constant of K2a=(2.7±0.4)×10-19 cm3 was determined and a rate constant of k2a=(2±1)×10-15 cm3 s-1 was roughly estimated. The effective adduct loss from the equilibrium can be explained by (i) an additional irreversible reaction of the adduct with O2 with a rate constant of (2.1±0.2)×10-16 cm3 s-1, or (ii) a unimolecular reaction of the peroxy radical, with a rate constant of (7.6±0.8)×102 s-1. For a reaction of the peroxy radical with O2 an upper limit of 1×10-17 cm3 s-1 is estimated. Addition of NO reveals formation of HO2 in the presence of O2 by recovering OH via HO2+NO. Applying numerical methods, reaction models were tested to describe the observed complex kinetics of OH. The data are consistent with rapid HO2 formation following a peroxy radical+NO reaction with a rate constant of (1.1±0.4)×10-11 cm3 s-1. Extrapolation of HO2 formation rates to [NO]=0 points at a second source of HO2 not preceded by any RO2+NO reaction.

The activation of Br- and Cl- to atomic Br and Cl in sea-spray aerosol was investigated in smog-chamber experiments. In the presence of O3, hydrocarbons and NaCl aerosol alone no activation was observed. By adding Br- to the aerosol, the chain reaction: Br + O3 ⇒ BrO, BrO + HO2 ⇒ HOBr, HOBr ⇒ HOBr(aq), HOBr(aq) + H+ + Br- ⇒ Br2 (6), HOBr(aq) + H+ + Cl- ⇒ BrCl (7) was verified. The step from reaction (6) to (7) is accompanied by a decrease of the Br-/Cl- ratio from 1/600 to less than 1/2000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with Br-. The pH value decreases to less than 2 during the first minutes of the experiment and later on to almost 1 (in the absence of NOx or SO2). This is caused by the formation of oxalic acid from alkanes and toluene. In stopped flow experiments, the reduction of Br2 by oxalic acid was observed to occur through a two-step mechanism: HC2O4- + Br2 ↔ Br- + BrC2O4H (k22, k-22), BrC2O4H ⇒ Br- + H+ + 2 CO2 (23) with the following rate constants and ratios of rate constants, k ± 2σ: k22k-23 / k-22 = (2.9 ± 0.3) · 10-4 s-1, k-22 / k-23 = 7000 ± 300013000 M-1, k22 = 2 ±-14 M-1 s-1, and k-23 > 0.1 s-1, k-22 > 600 M-1 s-1. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.

For the first time, high-resolution infrared gas-phase absorption spectra of the BrNO2 molecule were recorded using a Fourier-transform spectrometer. In this paper, the nu4 bands of the 79BrNO2 and 81BrNO2 isotopomers around 1670 cm-1 are investigated. Although the spectra are highly congested, rotational and centrifugal distortion constants for the ground and v4 = 1 states of 79BrNO2 and 81BrNO2 were determined. The results show that BrNO2 is a planar molecule of C2nu symmetry and confirm predictions from a recent ab initio study. Copyright 1998 Academic Press.

This paper presents the investigation of the photochemical reaction of chlorotoluron (3-(3-chloro-4-methyl-phenyl)-1,1-dimethylurea) in CH 3 CN, hexane, and aqueous and buffered solutions (pH = 4, 7, and 9) and of isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) in aqueous and buffered solutions using a polychromatic light source at a temperature of 22°C. For chlorotoluron, isosbestic points were found (with the exception of hexane as solvent) and ultraviolet spectroscopy was used to obtain kinetic data. The main photoproduct for the photolysis of chlorotoluron in aqueous solutions was identified as 3-(3-hydroxy-4-methyl-phenyl)-1,1 dimethylurea. Quantum yields found in aqueous and buffered solutions were comparable (about 0.07) and 2 times lower and 10 times higher in CH 3 CN and hexane, respectively. No isosbestic points were found for isoproturon, and quantum yields of about 0.004 were calculated in all solutions. Chlorotoluron and isoproturon present very low molar extinction coefficients above 290 nm, and they can be assumed to be photostable with respect to direct irradiation by sunlight.

The heterogeneous reactions leading to formation and loss of BrNO2 on salt solutions as a model substrate for atmospheric sea salt aerosol are investigated. Further to the reaction of ClNO2 with bromide solutions, the reaction of Br2 with nitrite solution was found to be a convenient method for the synthesis of BrNO2. We measured the temperature-dependent lifetime of BrNO2 in a quartz cell and obtained the activation energy EA = 89 ± 9 kJ/mol for the unimolecular decay at atmospheric pressure. The reactive uptake of BrNO2 and ClNO2 on water and aqueous solutions was determined using a wetted-wall flow tube technique. We observed the reactions Br2 + NO2- ↔ BrNO2 + Br-, Cl2 + NO2- → ClNO2 + Cl-, and the net reaction ClNO2 + Br- ↔ BrNO2 + Cl-. BrNO2 and ClNO2 both react with NO2- to release NO2 into the gas phase. Observed concentration profiles in the gas phase and in solution can be described qualitatively by a numerical model of the diffusion and reaction processes in the experimental setup.

The uptake kinetics of nitrosyl chloride (NOCl) by aqueous solutions has been measured as a function of temperature, using two different techniques, i.e., the wetted-wall at atmospheric and reduced...

The reaction of terbuthylazine (TBA) with OH radicals was investigated in an aerosol smog chamber (2400 L). TBA was adsorbed well below a monolayer on silicon dioxide as inert carrier. OH radicals were produced from hydrogen peroxide, ozone, and nitrogen dioxide. The OH concentrations span a region of 105 ≤ cOH/cm-3 ≤ 107 and were monitored by the consumption of butane, 2,2-dimethylbutane, pentafluorobenzene, 2,2,4,4-tetramethylbutane, and toluene as reference compounds. The OH rate constant of TBA obtained from nine smog chamber runs at T = 300 K on the aerosol is kOH(TBA) = (1.1 ± 0.2) × 10-11 cm3 s-1. Beside the OH reaction, a loss path not initiated by OH radicals was found (k = (1.9 ± 0.5) × 10-5 s-1), which can be explained only in part by loss processes observed in the dark. Using the OH rate constant determined on the aerosol as an estimate for the corresponding OH reaction in the environment, a half-life of about 1 day (with OH concentrations of 5−10 × 105 cm-3) is obtained. Using the UV spectrum...

Rate constants of the gas-phase reactions HO2 + NO → products (1), HO2 + NO → OH + NO2 (1a), and OH + NO → products (2) were determined at room temperature and total pressures of 10, 50, and 100 kPa of N2. OH radicals were produced by pulsed 248 nm photolysis of H2O2 and monitored by time-resolved CW UV-laser long-path absorption. Biexponential OH decay curves, observed in the presence of H2O2 and NO, were analyzed to obtain rate constants for the above reactions. Those of reactions 1 and 1a were found to be independent of pressure with averaged values of (9.7 ± 1.5) × 10-12 and (9.6 ± 1.5) × 10-12 cm3 s-1, respectively. This indicates an OH yield very close to unity (≥0.95) for the title reaction under the experimental conditions of this work. Error limits are estimated considering statistical and possible systematic errors. The pressure dependence found for reaction 2 is in good agreement with literature data. Rate constants of (1.3 ± 0.4) × 10-12, (4.7 ± 0.8) × 10-12, and (7.4 ± 1.3) × 10-12 cm3 s-1 ha...

The chemistry of N2O5 on liquid NaCl aerosols or bulk NaCl solutions was studied at 291 K by aerosol smog chamber and wetted-wall flow tube experiments. The uptake of N2O5 on deliquescent aerosol was obtained to be (3.2±0.2)×10−2 (1σ error) from the aerosol experiments. In the wetted-wall flow tube we observed that nitryl chloride (ClNO2) is the main product of the reaction at NaCl concentrations larger than approximately 0.5 M and almost the only product at concentrations larger than 1 M. The ClNO2 yield does not depend linearly on the NaCl concentration, especially at small sodium chloride concentrations (i.e., smaller than 1 M). It appeared that a simple mechanism where N2O5 undergoes two reaction channels (hydrolysis and reaction with Cl−) is unable to explain the observed concentration dependence of the product yield. We propose that N2O5 dissociates to NO2+ and NO3− (rate constant kl>104 s−1) mainly. The directly hydrolysis of N2O5 (k3[H2O]) is less than 20% of the total reaction. NO2+ reacts with water to form 2H+ and NO3− (k5) or with Cl− to form ClNO2 (k4). Neglecting the influence of ionic strength we evaluate k4/k5 to be 836±32 (1σ error). Using the wetted-wall flow tube technique, we studied the uptake of nitryl chloride by aqueous solutions containing NaCl. We observed that the uptake coefficient γ decreased from (4.84±0.13)×10−6 on pure water to (0.27±0.02)×10−6 on a 4.6 M NaCl solution. The sharp decrease of γ with increasing salt concentrations is evidence of reversible hydrolysis. ClNO2 dissociates to Cl− + NO2+(k6). In the absence of Cl− we evaluate H ⋅ k61/2 to be 0.44±0.01 mol L−1 atm−1 s−1/2. Finally, we discuss that atomic Cl from photolysis of ClNO2 may play a role in the marine boundary layer at high northern latitudes.

Time series of polychlorinated dioxins and furans (PCDD/F) and polychlorinated biphenyls (PCB) in ambient air of a large conurbation in North-Western Germany are presented and analyzed. The trend of PCDD/F concentrations, starting from as early as 1988, shows a pronounced decrease by at least one order of magnitude, demonstrating that the emission reductions were effective. The PCDD/F depositions also have decreased by a factor of 5 since 1992. However, both trends have leveled out since 2005. Time series of PCB concentrations and depositions starting in 1994 show only slight decreases for the concentrations and almost no decrease for the depositions. From the decay rates following first order kinetics, half-lives in the order of 5-15 years for the PCDD/F and 15-31 years for the sum of the six indicator PCB could be calculated, which are much longer than the half-lives estimated from their reactivity towards the OH radical. Apparently, small fresh emissions (PCDD/F), considerable secondary emissions and evaporation from contaminated soils slow down their decay in the atmosphere of big conurbations. Analyzing the decay rates of individual PCB congeners shows that the lower chlorinated and more volatile ones are removed faster than the higher chlorinated congeners, probably via gas phase reactions with the OH radical. It can be concluded from the present study that the input of PCDD/F and PCB into the food chain via the air path will continue for another one or two decades in big conurbations.

International audience; 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) x 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 (k(1a) + k(1b)) according to this simplified model. The Arrhenius plot reveals the step function typical of other aromatics and can be described using the expressions: 2 x 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 k(1a)/k(-1a) = 6 x 10(-26) exp(+9700 K/T) cm(3) is obtained at temperatures between 297 and 325 K and 2 x 10(-36) exp(+17 000 K/T) cm(3) at temperatures between 325 and 380 K.

The VUV absorption spectrum of phosgene, COCl 2 , was measured in the wavelength region between 161 and 220 nm using standard single-beam apparatus. Furthermore, quantum yield measurements were performed at 193 nm employing ArF laser photolysis and FTIR product analysis. Both the absorption cross section and quantum yield data are in reasonable agreement with data in the literature, while the occurrence of a pressure effect on the quantum yield still lacks a detailed explanation.

Photochemical reactions of atrazine, propazine, simazine, terbuthylazine, ametryn and atraton were investigated in aqueous and buffered (pH=7–9) solutions (containing a few percent of acetonitrile) using a polychromatic Xe light source at T=22[ddot]C. For terbuthylazine the photochemistry is investigated in detail, including solvent-, temperature-and pH-dependence and products found. The role of polychromatic light sources used in investigations of the photochemistry of triazines is discussed. For the first time, quantum yield measurements were performed in the UV-band between 240–300 nm of the chlorotriazines and ametryn. Isosbestic points were found in the UV-spectra at different irradiation times, and UV-spectroscopy was used to obtain kinetic information. Quantum yields in aqueous solutions at T=22[ddot]C for the chlorotriazines (Φ=0.048–0.062) and for ametryn (Φ=0.043) are comparable. The temperature dependence of the photoreaction of terbuthylazine leads to an activation energy of about 13 ...

A method for the synthesis of gaseous BrNO2 at concentrations of the order of 10-9 mol/cm3 at atmospheric pressure is described, based on the heterogeneous reaction of ClNO2 with aqueous bromide solutions. We measured the gas-phase infrared absorption cross sections in the range 700−1800 cm-1. The matrix isolation spectrum was recorded for identification by comparison with literature data.