P. Martín

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.

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.

A kinetic study of gas-phase reaction of thiophene with NO3 by using absolute and relative methods

Abstract The gas-phase rate coefficient for the reaction of thiophene with nitrate radical, NO3, has been determined, using relative (gas chromatography as analytical tool) and absolute methods at 298 K. The absolute experiments were carried out using a fast-flow-discharge technique, with detection of the NO3 radical by Laser Induced Fluorescence (LIF). The proposed rate coefficient at 298 K is, k=(3.16±0.27)×10 −14 cm 3 molecule −1 s −1 . The temperature dependence was studied by the absolute technique in the range 260–433 K, observing that in the interval of 260–277 K the rate coefficient decreases as the temperature increases and from 298 K onwards the rate coefficient increases with temperature.

Gas-phase rate coefficients and activation energies for the reaction of NO3 radicals with selected branched aliphatic aldehydes

Using a fast-flow-discharge technique, absolute rate coefficients for the gas-phase reactions of the NO3 radical with a series of branched aldehydes (2-methylpropanal, 2,2-dimethylpropanal, 2-methylbutanal and 3-methylbutanal) have been determined. The experiments were carried out monitoring the NO3 radical by laser induced fluorescence (LIF). The temperature dependence of the reaction was studied in the range between 298 and 433 K. The proposed Arrhenius expressions, are respectively: k 1 = (1.0 ± 0.5) × 10−10exp[−(2598 ± 384)/T]/cm3 molecule−1 s−1, k 2 = (2.7 ± 1.2) × 10−11exp[−(2063 ± 356)/T]/cm3 molecule−1 s−1, k 3 = (5.5 ± 3.1) × 10−11exp[−(2296 ± 555)/T]/cm3 molecule−1 s−1, k 4 = (3.7 ± 1.4) × 10−11exp[−(2184 ± 230)/T]/cm3 molecule−1 s−1. Tropospheric lifetimes for these aldehydes have been calculated at night and during the daytime for typical NO3 and OH average concentrations.

A TEMPERATURE DEPENDENCE STUDY OF THE GAS-PHASE REACTION OF THE NITRATE RADICAL WITH 3-FLUOROPROPENE FOLLOWED BY LASER INDUCED FLUORESCENCE DETECTION

Absolute rate coefficient for the gas-phase reaction of NO3 with 3-fluoropropene has been measured using the discharge-flow technique coupled to a LIF detection system for a range of temperatures from 296 K to 430 K. The measured room temperature rate constant is (0.39 ± 0.02) × 10−14 molecule−1 cm3 s−1. The Arrhenius expression k = (7.17 ± 3.34) × 10−12 exp[−(2248 ± 169)/T] is proposed for the reaction. The reactivity of alkenes containing halogen atoms is discussed and compared to that of simple alkenes, on the basis of the correlations between the reactivity against NO3 and the ionization potential of the alkenes. Tropospheric half life of 3-fluoropropene has been estimated at night and during daytime for typical NO3 and OH trophospheric concentrations.

Night-Time Atmospheric Reactivity of Some Oxygenated Organic Compounds

The nitrate radical (NO3) is the most important atmospheric oxidant during the night-time for organic volatile compounds. In the review reported here, the available kinetic and product data for nitrate radical reactions with a series of oxygenated volatile organic compounds (OVOCs) are reviewed. The results cover the reactivity of NO3 towards unsaturated aldehydes, aliphatic alcohols and acrylate esters. The kinetic results obtained by different research groups on using various experimental techniques are compared and discussed. Trends in reactivity are analyzed, and studies on the primary reaction products, when available, are presented. The reaction mechanisms elucidated from the kinetic and product data are presented and discussed.

Monitoring Studies of Urban Air Quality in Central-Southern Spain Using Different Techniques

In urban areas, emissions of air pollutants by anthropogenic processes such as traffic, industry, power plants and domestic heating systems are the main sources of pollution (Fenger, 1999). The massive growth in road traffic and in the use of fossil fuels during the last decades has changed the composition of urban air, increasing the frequency of pollution episodes and the number of cities experiencing them. The main pollutants monitored in the atmosphere in these areas are ozone (O3), nitrogen oxides (NOx), sulphur dioxide (SO2), carbon monoxide (CO), aromatic compounds and particulate matter. While CO, NO and aromatic compounds are mainly emitted by traffic, O3 and NO2 are originated by photochemical reactions.