Romeo Iulian Olariu

Rate coefficients for the gas‐phase reaction of OH radicals with selected dihydroxybenzenes and benzoquinones

Rate coefficients have been determined for the gas-phase reaction of the hydroxyl (OH) radical with the aromatic dihydroxy compounds 1,2-dihydroxybenzene, 1,2-dihydroxy-3-methylbenzene and 1,2-dihydroxy-4-methylbenzene as well as the two benzoquinone derivatives 1,4-benzoquinone and methyl-1,4-benzoquinone. The measurements were performed in a large-volume photoreactor at (300 ± 5) K in 760 Torr of synthetic air using the relative kinetic technique. The rate coefficients obtained using isoprene, 1,3-butadiene, and E-2-butene as reference hydrocarbons are kOH(1,2-dihydroxybenzene) = (1.04 ± 0.21) × 10−10 cm3 s−1, kOH(1,2-dihydroxy-3-methylbenzene) = (2.05 ± 0.43) × 10−10 cm3 s−1, kOH(1,2-dihydroxy-4-methylbenzene) = (1.56 ± 0.33) × 10−10 cm3 s−1, kOH(1,4-benzoquinone) = (4.6 ± 0.9) × 10−12 cm3 s−1, kOH(methyl-1,4-benzoquinone) = (2.35 ± 0.47) × 10−11 cm3 s−1. This study represents the first determination of OH radical reaction-rate coefficients for these compounds.

Investigations on the gas-phase photolysis and OH radical kinetics of methyl-2-nitrophenols

Methyl-2-nitrophenols can be emitted directly to the atmosphere or can be formed in situ via the oxidation of aromatic hydrocarbons. Nitrophenols possess phytotoxic properties and recent studies indicate their photooxidation is effective in producing secondary organic aerosols. Therefore, investigations on the major photooxidation pathways of these compounds with respect to assessing their environmental impacts and effects on human health are highly relevant. Presented here are determinations of the rate coefficients for the reactions of OH radicals with four methyl-2-nitrophenol isomers using a relative kinetic technique. The experiments were performed in a 1080 l photoreactor at (760 +/- 10) Torr total pressure of synthetic air at (296 +/- 3) K. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) have been obtained: 3-methyl-2-nitrophenol, (3.69 +/- 0.70) x 10(-12); 4-methyl-2-nitrophenol, (3.59 +/- 1.17) x 10(-12); 5-methyl-2-nitrophenol, (6.72 +/- 2.14) x 10(-12); 6-methyl-2-nitrophenol, (2.70 +/- 0.57) x 10(-12). Photolysis of the methyl-2-nitrophenols with the superactinic fluorescent lamps (320 < lambda < 480 nm, lambda(max) = 360 nm) used in the experiments was observed. Photolysis frequencies measured for the methyl-2-nitrophenols in the photoreactor have been determined and scaled to atmospheric conditions. The results suggest that photolysis rather than the reaction with OH radicals will be the dominant gas phase atmospheric loss process for methyl-2-nitrophenols.

GC × GC-MS HYPHENATED TECHNIQUES FOR THE ANALYSIS OF VOLATILE ORGANIC COMPOUNDS IN AIR

Comprehensive two-dimensional gas chromatography (GC × GC) and its direct applications to measurement of volatile and semivolatile organic compounds in air are reviewed and discussed. The paper includes a brief discussion of the instrumental set-up and theory for the comprehensive GC × GC hyphenated with different detection techniques. Several reviewed types of modulators demonstrate that the applications of comprehensive GC × GC are still under development, underlying the flexibility of the system as well. The fundamental differences between one-dimensional and two-dimensional gas chromatography, regarding their potential to provide both qualitative and quantitative information, are also presented. The present article focuses on reported applications dealing with the analysis of volatile and semivolatile organic compounds from air (gas and particles related), but some data related to other sample types analyzed with comprehensive GC × GC are also briefly presented. The paper supports the idea that there is a good reason for interest in comprehensive GC × GC, which seems to be a suitable technique for applications in the separation of complex mixtures of volatile and semivolatile compounds.

Development of a New Flow Reactor for Kinetic Studies. Application to the Ozonolysis of a Series of Alkenes

A new flow reactor has been developed to study ozonolysis reactions at ambient pressure and room temperature (297 ± 2 K). The reaction kinetics of O(3) with 4-methyl-1-pentene (4M1P), 2-methyl-2-pentene (2M2P), 2,4,4-trimethyl-1-pentene (tM1P), 2,4,4-trimethyl-2-pentene (tM2P) and α-pinene have been investigated under pseudo-first-order conditions. Absolute measurements of the rate coefficients have been carried out by recording O(3) consumption in excess of organic compound. Alkene concentrations have been determined by sampling adsorbent cartridges that were thermodesorbed and analyzed by gas-chromatography coupled to flame ionization detection. Complementary experimental data have been obtained using a 250 L Teflon smog chamber. The following ozonolysis rate coefficients can be proposed (in cm(3) molecule(-1) s(-1)): k(4M1P) = (8.23 ± 0.50) × 10(-18), k(2M2P) = (4.54 ± 0.96) × 10(-16), k(tM1P) = (1.48 ± 0.11) × 10(-17), k(tM2P) = (1.25 ± 0.10) × 10(-16), and k(α-pinene) = (1.29 ± 0.16) × 10(-16), in very good agreement with literature values. The products of tM2P ozonolysis have been investigated, and branching ratios of (21.4 ± 2.8)% and (73.9 ± 7.3)% have been determined for acetone and 2,2-dimethyl-propanal, respectively. Additionally, a new nonoxidized intermediate, 2-methyl-1-propene, has been identified and quantified. A topological SAR analysis was also performed to strengthen the consistency of the kinetic data obtained with this new flow reactor.

The Mechanism of Pyrolysis of Benzyl Azide: Spectroscopic Evidence for Benzenemethanimine Formation

We study the gas-phase pyrolysis of benzyl azide (BA, C6H5CH2N3) using ultraviolet photoelectron spectroscopy (UVPES) and matrix-isolation infrared (IR) spectroscopy, together with electronic structure calculations and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. It is found that BA decomposes via N2 elimination at ca. 615 K, primarily yielding benzenemethaninime. Other end products include HCN and C6H6. N-Methyleneaniline is not detected, although its formation at higher temperature is foreseen by RRKM calculations.

Kinetic Study of the Gas-Phase Reactions of Chlorine Atoms with 2-Chlorophenol, 2-Nitrophenol, and Four Methyl-2-nitrophenol Isomers

Anthropogenic activities are the main source of nitrophenols and chlorophenols in the atmosphere. Nitro and chlorophenols have a high potential to form ozone and secondary organic aerosol, thus investigations on the major photo oxidation pathways of these compounds are important to assess their contribution to urban air pollution and human health. Presented here are rate coefficients determined at atmospheric pressure and (298 ± 2) K using a relative kinetic method for the reactions of chlorine atoms with 2-chlorophenol (2ClP), 2-nitrophenol (2NP) and four methyl-2-nitrophenol (2-nitrocresol, nM2NP (n = 3,4,5,6)) isomers. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) have been obtained: (5.9 ± 1.5) × 10(-12) for 2ClP, (6.8 ± 2.3) × 10(-12) for 2NP, and (14.0 ± 4.9) × 10(-11), (4.3 ± 1.5) × 10(-11), (1.94 ± 0.67) × 10(-11) and (2.68 ± 0.75) × 10(-11) for the four methyl-2-nitrophenol isomers 3M2NP, 4M2NP, 5M2NP, and 6M2NP, respectively. This study represents the first kinetic investigation for the reaction of chlorine atoms with all the nitrophenols. In addition, to assist in the interpretation of the results, rate coefficients for the reactions of Cl atoms with the cresol ortho, meta, and para isomers have been determined for the first time. The rate coefficient for the reaction with 2ClP is in good agreement with previous data and the relative reactivity of 2NP, 4M2NP, 5M2NP, and 6M2NP can be rationalized based on known substituent effects. The rate coefficient for 3M2NP is anomalously large; the observation of significant NO2 production in only this reaction suggests that an ipso substitution mechanism is the cause of the enhanced reactivity.

Chemical characteristics of size resolved atmospheric aerosols in Iasi, north-eastern Romania. Nitrogen-containing inorganic compounds controlling aerosols chemistry in the area

This study assesses the atmospheric aerosol load and behaviour (size and seasonal dependent) of the major inorganic and organic aerosol ionic components (i.e., acetate, (C2H3O2), formate, (HCO2), fluoride, (F–), chloride, (Cl–), 15 nitrite, (NO2), nitrate, (NO3), phosphate, (PO4), sulfate, (SO4), oxalate, (C2O4), sodium, (Na+), potassium, (K+), ammonium, (NH4), magnesium, (Mg2+) and calcium (Ca2+), in Iasi urban area, north-eastern Romania. Continuous measurements were carried out over 2016 by means of a cascade Dekati Low-Pressure Impactor (DLPI) performing aerosol size classification in 13 specific fractions evenly distributed over the 0.0276 up to 9.94 μm size range. Fine particulate Cl–, NO3, NH4 and K+ exhibited clear minima during the warm seasons and clear maxima over the cold seasons, mainly 20 controlled by corroboration between factors such as enhancement in the emission sources, changes in the mixed layer depth and specific meteorological conditions. Fine particulate SO4 did not show much variation with respect to seasons. Particulate NH4 and NO3 ions were identified as critical parameters controlling aerosols chemistry in the area. The measured concentrations of particulate NH4 and NO3 in fine mode (PM2.5) aerosols were found to be in reasonable good agreement with modelled values for winter but not for summer, an observation reflecting actually the susceptibility of 25 NH4NO3 aerosols to be lost due to volatility over the warm seasons. Clear evidences have been obtained for the fact that in Iasi, north-eastern Romania, NH4 in PM2.5 is primarily associated with SO4 and NO3 but not with Cl–. However, indirect ISORROPIA-II estimations showed that the atmosphere in the investigated area might be ammonia-rich during both the cold and warm seasons, such as enough NH3 to be present to neutralize H2SO4, HNO3 and HCl acidic components and to generate fine particulate ammonium salts, in the form of (NH4)2SO4, NH4NO3 and NH4Cl. ISORROPIA-II runs allowed us estimating 30 that over the warm seasons ~ 35 % of the total analyzed samples presented pH values in the very strong acidity fraction (0–3 Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1030 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 17 November 2017 c