Ernesto Martínez

A Pulsed Laser Photolysis-Resonance Fluorescence Kinetic Study of the Atmospheric Cl Atom-Initiated Oxidation of Propene and a Series of 3-Halopropenes at Room Temperature

Absolute rate coefficient measurements have been carried out for the reactions of Cl atoms with propene and a series of 3-halopropenes, at room temperature (298 ± 2) K using a newly constructed laser photolysis-resonance fluorescence (PLP-RF) system. The rate coefficients obtained (in units of cm3 molecule−1 s−1) are: propene (1.40± 0.24) ×10−10, 3-fluoropropene (4.92 ± 0.42) ×10−11, 3-chloropropene (7.47 ± 1.50) × 10−11, 3-bromopropene (1.23± 0.14) ×10−10 and 3-iodopropene (1.29± 0.15) ×10−10. In order to test this new system, the reactions of Cl atoms with acetone and isoprene have also been studied and compared with data previously reported. The rate coefficients determined at room temperature for these last two reactions are (2.93 ± 0.20) ×10−12 cm3 molecule−1 s− 1 and (3.64± 0.20)×10−10 cm3 molecule−1 s−1, respectively. The measured values were independent of pressure over the range 20–200 Torr. The influence of the different halogen atoms substituents on the reactivity of these alkenes with Cl atoms as well as the atmospheric implications of these measurements are studied and discussed for the first time in this work and compared with the reactivity with NO3 and OH radicals.

Gas-phase chemistry of atmospheric Cl atoms : a PLP-RF kinetic study with a series of ketones

The pulsed laser photolysis-resonance fluorescence technique (PLP-RF) has been used to determine the absolute rate coefficients for the gas-phase reactions of Cl atoms with a series of ketones at room temperature (298 K). The rate coefficients obtained (in units of cm 3 molecule -1 s -1 ) are: 2-butanone (3.30±0.20) × 10- 11 , 2,3-butadione (4.92±0.44) × 10 -13 , 2-pentanone (4.57±0.28) × 10 -11 , 3-pentanone (4.50±0.32) × 10 -11 , 2-hexanone (6.54±0.58) x 10 -11 , 3-hexanone (6.69±0.62) x 10 -11 and cyclohcxanone (6.75±0.52) x 10 -11 . The measured values were independent of pressure over the range 20-200 Torr. These rate coefficients were compared with previous studies carried out by different techniques, when data were available. Results and atmospheric implications are discussed and compared with the reactivity with OH radicals.

Molecular structure of p-methylaniline and its van der Waals complexes with CF3H, CH4 and CF4 studied by laser induced fluorescence spectroscopy and ab initio calculations

Abstract The UV fluorescence excitation and dispersed fluorescence spectra of jet-cooled p -methylaniline have been obtained for the S 1 ←S 0 transition. The main spectral bands have been assigned by comparison with those of other relevant substituted benzenes and with the help of computed vibrational frequencies. The structure of p -methylaniline in both the S 0 and S 1 states has been studied at ab initio quantum chemical calculations at MP2 and CIS levels of theory using the 6-31+G ∗ basis sets. Both low- and high-resolution laser induced fluorescence spectra of p -methylaniline van der Waals complexes with CF 3 H, CH 4 and CF 4 have been characterised following jet-expansion investigations. The equilibrium geometries in the ground state of the complexes have been calculated at MP2/6-31+G ∗ level of calculation and their rotational contour have been simulated for all the complexes studied.

Absolute Rate Coefficients for the Gas-Phase Reactions of NO3 Radical with a Series of Monoterpenes at T = 298 to 433 K

The aim of this work is to study the reactivity of some naturally emitted terpenes, 2-carene, sabinene, myrcene, α-phellandrene, d-limonene, terpinolene and γ-terpinene, towards NO3 radical to evaluate the importance of these reactions in the atmosphere and their atmospheric impact. The experiments with these monoterpenes have been carried out under second-order kinetic conditions over the range of temperature 298–433 K, using a discharge flow system and monitoring the NO3 radical by Laser Induced Fluorescence (LIF). This work is the first temperature dependence study for the reactions of the nitrate radical with the above-mentioned monoterpenes. The measured rate constants at 298 K for the reaction of NO3 with such terpenes are as follows: 2-carene, 16.6 ± 1.8, sabinene 10.7 ± 1.6, myrcene 12.8 ± 1.1, α-phellandrene 42 ± 10, d-limonene 9.4 ± 0.9, terpinolene 52 ± 9 and γ-terpinene 24 ± 7, in units of 10-12 cm3 molecule-1 s-1. The proposed Arrhenius expressions, for the reactions of NO3 with 2-carene, sabinene, myrcene and α-phellandrene are, respectively k1 = (1.4 ± 0.7) × 10-12 exp[(741 ± 190/T)] (cm3 molecule-1 s-1), k2=(2.3 ± 1.3) × 10-10 exp[−(940 ± 200/T)] (cm3 molecule-1 s-1), k3 = (2.2 ± 0.2) × 10-12 exp[(523 ± 35/T)] (cm3 molecule1 s-1) and k4 = (1.9 ± 1.3) × 10-9 exp[−(1158 ± 270/T)] (cm3 molecule-1 s-1). A decrease in the rate constants when raising the temperature has also been found for the reaction of d-limonene with NO3 while an increase in the rate constant with temperature has been observed for the reactions of terpinolene and γ-terpinene with NO3. Tropospheric half-lives for these terpenes have been calculated at night and during the day for typical NO3 and OH concentrations showing that both radicals provide an effective tropospheric sink for these compounds and that the night-time reaction with NO3 radical can be an important, if not dominant, loss process for these naturally emitted organics and for NO3 radicals.

Atmospheric Lifetimes and Global Warming Potentials of CF3CH2CH2OH and CF3(CH2)2CH2OH

A comprehensive study of several atmospheric degradation routes for two hydrofluoroalcohols, CF(3)(CH(2))(x=1,2)CH(2)OH, is presented. The gas-phase kinetics of their reactions with hydroxyl radicals (OH) and chlorine (Cl) atoms are investigated by absolute and relative techniques, respectively. The room-temperature rate coefficients (±σ, in cm(3) molecule(-1) s(-1)) k(OH) and k(Cl), are respectively (9.7±1.1)×10(-13) and (1.60±0.45)×10(-11) for CF(3)CH(2)CH(2)OH, and (2.62±0.32)×10(-12) and (8.71±0.24)×10(-11) for CF(3)(CH(2))(2)CH(2)OH. Average lifetimes of CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH due to the OH and Cl reactions are estimated to be 12 and 4 days, and greater than 20 and 4 years, respectively. Also, the IR and UV absorption cross sections of CF(3)(CH(2))(x=1,2)CH(2)OH are determined in the spectral ranges of 500-4000 cm(-1) and 200-310 nm. Photolysis of CF(3)(CH(2))(x=1,2)CH(2)OH in the actinic region (λ≥290 nm) is negligible compared to their homogeneous removal. Additionally, computational IR spectra are consistent with the experimental ones, thus giving high confidence in the obtained results. The lifetimes of CF(3)(CH(2))(x=1,2)CH(2)OH and IR spectra reported herein allow the calculation of the direct global warming potential of these hydrofluoroalcohols. The contribution of CF(3)(CH(2))(x)CH(2)OH to radiative forcing of climate change will be negligible.

A kinetic study of the reaction of Cl with a series of linear and ramified ketones as a function of temperature

The reactions of Cl atoms with 2,3-butadione (k1), 2-butanone (k2), 2-pentanone (k3), 2-hexanone (k4), 3-methyl-2-butanone (k5), 4-methyl-2-pentanone (k6) and 5-methyl-2-hexanone (k7), were investigated for the first time as a function of temperature (266–380 K), over the pressure range 20–200 Torr, using pulsed laser photolysis-resonance fluorescence (PLP-RF). The Arrhenius expressions for the seven reactions are proposed. The temperature dependence of the studied reactions is discussed; the reaction of Cl atoms with 2,3-butadione exhibits a positive temperature dependence whereas the corresponding reactions with 2-pentanone, 2-hexanone, 4-methyl-2-pentanone and 5-methyl-2-hexanone exhibit a negative temperature dependence and those with 2-butanone and 3-methyl-2-butanone shows only a slightly positive and a negative temperature dependence, respectively. Finally, the results and atmospheric implications are discussed and compared with the reactivity towards the OH radical.

An Experimental Study on the Temperature Dependence for the Gas-Phase Reactions of NO3 Radical with a Series of Aliphatic Aldehydes

The absolute rate constants for the gas-phasereactions of the NO3 radical with a series ofaldehydes such as acetaldehyde, propanal, butanal,pentanal, hexanal and, heptanal were measured overthe temperature range 298–433 K, using a dischargeflow system and monitoring the NO3 radical byLaser Induced Fluorescence (LIF).The measured rate constants at 298 K for thereaction of NO3, in units of 10−14 cm3molecule−1 s−1, were as follows:acetaldehyde 0.32 ± 0.04, propanal 0.60 ± 0.06, butanal 1.46± 0.16, pentanal 1.75 ±0.06, hexanal 1.83 ± 0.36, and heptanal 2.37 ±0.42. The proposed Arrhenius expressions arek1 = (6.2 ± 7.5) × 10−11 exp[−(2826 ± 866)/T] (cm3 molecule−1s−1),k2 = (1.7 ± 1.0) × 10−11 exp[−(2250 ± 192)/T] (cm3 molecule−1s1), k3 =(7.6 ± 9.8) × 1011 exp[−(2466 ± 505)/T] (cm3 molecule−1s−1),k4 = (2.8 ± 1.4) × 10−11 exp[−(2189 ± 156)/T] (cm3 molecule−1s−1), k5 = (7.0 ± 1.8) ×10−11 exp [−(2382 ± 998)/T](cm3 molecule−1 s−1), andk6 = (7.8 ± 1.0) × 10−11 exp[−(2406 ± 481)/T](cm3 molecule−1 s−1).Tropospheric lifetimes for these aldehydes werecalculated at night and during the day for typicalNO3 and OH average concentrations and showed thatboth radicals provide an effective tropospheric sinkfor these compounds and that the night-time reactionwith the NO3 radical can be an important, if notdominant, loss process for these emitted organics andfor NO3 radicals.

Temperature dependence of the reactions of the nitrate radical with dichloroalkenes followed by LIF detection

Absolute rate coefficients for the reaction of NO3 with 1,1-dichloropropene, 2,3-dichloropropene and (E)-1,3-dichloropropene have been measured using the discharge-flow technique coupled to an LIF detection system for a range of temperatures from 296 to 430 K. The measured room-temperature rate constants are (1.52 ± 0.76)× 10–14, (1.39 ± 0.30)× 10–14 and (0.95 ± 0.14)× 10–14 cm3 molecule–1 s–1, respectively. The Arrhenius expressions k=(2.85 ± 1.21)× 10–11 exp[–(2274 ± 313)/T], k=(0.16 ± 0.02)× 10–11 exp[–(1420 ± 82)/T], k=(5.86 ± 1.60)× 10–11 exp[(–2575 ± 192)/T] cm3 molecule–1 s–1, are proposed for the three reactions.The reactivity of alkenes containing vinylic halogen atoms is discussed and compared with that of simple alkenes. A dependence of room-temperature rate constants and energy of activation on haloalkene ionization potential, corrected for the strength of the mesomeric interaction between the chlorine atom and the carbon–carbon π bond, is found.Tropospheric half lives of these compounds have been estimated at night and during the day for typical NO3 and OH tropospheric concentrations, in order to assess the lifetime of these compounds in the atmosphere.

Levels and sources of volatile organic compounds including carbonyls in indoor air of homes of Puertollano, the most industrialized city in central Iberian Peninsula. Estimation of health risk.

Twenty nine organic air pollutants including carbonyl compounds, alkanes, aromatic hydrocarbons and terpenes were measured in the indoor environment of different houses together with the corresponding outdoor measurements in Puertollano, the most industrialized city in central Iberian Peninsula. VOCs were sampled during 8 weeks using Radiello(®) passive samplers, and a questionnaire on potential VOCs sources was filled out by the occupants. The results show that formaldehyde and hexanal was the most abundant VOCs measured in indoor air, with a median concentration of 55.5 and 46.4μgm(-3), respectively followed by butanal (29.1μgm(-3)), acetone (28.4μgm(-3)) and acetaldehyde (21.4μgm(-3)). After carbonyls, n-dodecane (13.1μgm(-3)) and terpenes (α-pinene, 13.4μgm(-3) and limonene, 13.4μgm(-3)) were the compounds with higher median concentrations. The indoor/outdoor (I/O) ratios demonstrated that sources in the indoor environment are prevailing for most of the investigated VOCs especially for limonene, α-pinene, hexanal, formaldehyde, pentanal, acetaldehyde, o-xylene, n-dodecane and acetone with I/O ratio >6. Multiple linear regressions were applied to investigate the indoor VOC determinants and Spearman correlation coefficients were used to establish common sources between VOCs. Finally, the lifetime cancer risk associated to formaldehyde, acetaldehyde and benzene exposure was estimated and they varied from 7.8×10(-5) to 4.1×10(-4) for formaldehyde, from 8.6×10(-6) to 3.5×10(-5) for acetaldehyde and from 2.0×10(-6) to 1.5×10(-5) for benzene. For formaldehyde, the attributed risk in most sampled homes was two orders of magnitude higher than the one (10(-6)) proposed as acceptable by risk management bodies.

Kinetic study of the reactions of NO3 with 3-chloropropene, 3-bromopropene and 3-iodopropene using LIF detection

The kinetics of the reactions of the nitrate radical, NO3, with 3-chloropropene and 3-bromopropene have been studied in the temperature range 296–428 K, using the discharge-flow technique coupled to detection of NO3 by laser-induced fluorescence. The results obtained for the room-temperature rate constants are (0.49 ± 0.02)× 10–14 and (0.38 ± 0.02)× 10–14 cm3 molecule–1 s–1, respectively, and the proposed Arrhenius expressions are k=(1.92 ± 0.79)× 10–11 exp[(– 2480 ± 143/T)] and k=(1.27 ± 0.37)× 10–12 exp[(– 1737 ± 104)/T] cm3 molecule–1 s–1, respectively (errors quoted as σ).The study of the reaction between the NO3 radical and 3-iodopropene has also been attempted using the same conditions. The decomposition of 3-iodopropene with increasing temperature and the occurrence of some radical–radical reactions makes it difficult to establish the Arrhenius parameters. A room-temperature rate constant of k⩽ 3.91 ± 0.02 × 10–14 cm3 molecule–1 s–1 has been estimated.An estimate of the corresponding rate coefficients for the reactions of these halopropenes with the OH radical has been made. Tropospheric half-lives are calculated at night and during the day for typical NO3 and OH concentrations, and show that both radicals provide an effective tropospheric sink for these compounds.