The kinetics and mechanisms of the gas-phase reactions of NO3 radical with two branched unsaturated aldehydes, 2-methyl-2-butenal (also called 2-methyl-crotonaldehyde) and 3-methyl-2-butenal (or ...3-methyl-crotonaldehyde), have been investigated by experimental and theoretical approaches. Kinetic data were also provided, for comparison, for 2-butenal (or crotonaldehyde). Experiments were performed in a simulation chamber at 295 ± 3 K and atmospheric pressure. Rate constants were determined using both absolute and relative rate methods. Experimental results were found to be in good agreement leading to the following rate constants (in cm3 molecule–1 s–1): k(2-butenal + NO3) = (4.6 ± 1.3) × 10–15; k(2-methyl-2-butenal + NO3) = (14.0 ± 2.8) × 10–15; and k(3-methyl-2-butenal + NO3) = (19.1 ± 4.1) × 10–15. Theoretical calculations were also performed using the DFT-BH&HLYP/6-311++G(d,p) method and lead to rate constants in agreement with experiments and allow us to explore mechanisms for abstraction and addition pathways. Impact on atmospheric chemistry is discussed.
Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. They can
rapidly react with the nitrate radical (NO3) during the nighttime to form a
number ...of functionalized products. Among them, organic nitrates (ONs) have
been shown to behave as reservoirs of reactive nitrogen and consequently
influence the ozone budget and secondary organic aerosols (SOAs), which are
known to have a direct and indirect effect on the radiative balance and
thus on climate. Nevertheless, BVOC + NO3 reactions remain poorly understood. Thus,
the primary purpose of this study is to furnish new kinetic and mechanistic
data for one monoterpene (C10H16), terpinolene, and one
sesquiterpene (C15H24), β-caryophyllene, using simulation
chamber experiments. These two compounds have been chosen in order to
complete the few experimental data existing in the literature. Rate
constants have been measured using both relative and absolute methods. They
have been measured to be (6.0 ± 3.8) ×10-11 and (1.8 ± 1.4) ×10-11 cm3 molec.−1 s−1 for
terpinolene and β-caryophyllene respectively. Mechanistic studies
have also been conducted in order to identify and quantify the main reaction
products. Total organic nitrates and SOA yields have been determined. Both
terpenes appear to be major ON precursors in both gas and particle phases
with formation yields of 69 % for terpinolene and 79 % for β-caryophyllene respectively. They are also major SOA precursors, with
maximum SOA yields of around 60 % for terpinolene and 90 % for β-caryophyllene. In order to support these observations, chemical analyses
of the gas-phase products were performed at the molecular scale using
a proton transfer reaction–time-of-flight–mass spectrometer (PTR-ToF-MS) and FTIR. Detected products allowed proposing chemical mechanisms
and providing explanations through peroxy and alkoxy reaction pathways.
The interactions between SO2 and natural salt aerosol particles represent complex and crucial dynamics within atmospheric processes and the broader climate system. This study investigated the SO2 ...uptake, hygroscopicity, morphology and mixing states of natural salt particles, which are generated from brines sampled from the Chaka salt lake located in the Qinghai-Tibet plateau. A comparison with atomized pure NaCl particles is included as reference. The results show that NaCl particles exhibit the lowest SO2 uptake, while Chaka salt particles demonstrate higher uptake due to their complex composition. The hygroscopicity of salt particles is influenced by several factors, including chemical complexity, SO2 exposure and light conditions. In comparison to pure NaCl, Chaka salt displays higher hygroscopicity, which is further enhanced in the presence of SO2. However, when exposed to light, mass growth is suppressed, suggesting the formation of species with lower hygroscopicity, such as Na2SO4. Analysis of particle morphology and mixing states reveals notable distinctions between NaCl crystals and Chaka salt particles, where the Chaka salt particles exhibit rounded shapes with a structure composed of cubic NaCl cores surrounded by sulfate materials as a coating. In addition, the chemical morphology analysis also reveals that the particles show morphological and spectral changes before and after the exposure to SO2, light and high RH. Therefore, this research highlights the intricate interactions between SO2 and natural salt aerosol particles in diverse environmental settings, underscoring their multifaceted impacts on atmospheric processes.
•Natural salt particles show higher SO2 uptake than pure NaCl particles.•The hygroscopicity is influenced by chemical complexity, SO2 exposure, and light conditions.•Light exposure suppresses hygroscopic growth, potentially leading to the formation of less hygroscopic species.•Natural salt particles exhibit rounded shapes with cubic NaCl cores encased in sulfate coatings.•Particles exhibit morphological and spectral changes after exposure to SO2, light, and high RH.
The influence of the precursor chemical structure on secondary organic aerosol (SOA) formation was investigated through the study of the ozonolysis of two anthropogenic aromatic alkenes: ...2-methylstyrene and indene. Experiments were carried out in three different simulation chambers: ICARE 7300L FEP Teflon chamber (ICARE, Orléans, France), EUPHORE FEP Teflon chamber (CEAM, Valencia, Spain), and CESAM evacuable stainless steel chamber (LISA, Créteil, France). For both precursors, SOA yield and growth were studied on a large range of initial concentrations (from ∼60 ppbv to 1.9 ppmv) and the chemical composition of both gaseous and particulate phases was investigated at a molecular level. Gas phase was described using FTIR spectroscopy and online gas chromatography coupled to mass spectrometry, and particulate chemical composition was analyzed (i) online by thermo-desorption coupled to chemical ionization mass spectrometry and (ii) offline by supercritical fluid extraction coupled to gas chromatography and mass spectrometry. The results obtained from a large set of experiments performed in three different chambers and using several complementary analytical techniques were in very good agreement. SOA yield was up to 10 times higher for indene ozonolysis than for 2-methylstyrene ozonolysis at the same reaction advancement. For 2-methylstyrene ozonolysis, formaldehyde and o-tolualdehyde were the two main gaseous phase products while o-toluic acid was the most abundant among six products detected within the particulate phase. For indene ozonolysis, traces of formic and phthalic acids as well as 11 species were detected in the gaseous phase and 11 other products were quantified in the particulate phase, where phthaldialdehyde was the main product. On the basis of the identified products, reaction mechanisms were proposed that highlight specific pathways due to the precursor chemical structure. These mechanisms were finally compared and discussed regarding SOA formation. In the case of 2-methylstyrene ozonolysis, ozone adds mainly on the external and monosubstituted double bond, yielding only one C8- and monofunctionalized Criegee intermediate and hence more volatile products as well as lower SOA mass than indene ozonolysis in similar experimental conditions. In the case of indene, ozone adds mainly on the five-carbon-ring and disubstituted CC double bond, leading to the formation of two C9- and bifunctionalized Criegee intermediates, which then evolve via different pathways including the hydroperoxide channel and form highly condensable first-generation products.
Residential biomass burning for heating purposes is an important source of air pollutants during winter. Here we test the hypothesis that significant secondary organic aerosol production can take ...place even during winter nights through oxidation of the emitted organic vapors by the nitrate (NO3) radical produced during the reaction of ozone and nitrogen oxides. We use a mobile dual smog chamber system which allows the study of chemical aging of ambient air against a control reference. Ambient urban air sampled during a wintertime campaign during nighttime periods with high concentrations of biomass burning emissions was used as the starting point for the aging experiments. Biomass burning organic aerosol (OA) was, on average, 70 % of the total OA at the beginning of our experiments. Ozone was added in the perturbed chamber to simulate mixing with background air (and subsequent NO3 radical production and aging), while the second chamber was used as a reference. Following the injection of ozone, rapid OA formation was observed in all experiments, leading to increases in the OA concentration by 20 %–70 %. The oxygen-to-carbon ratio of the OA increased on average by 50 %, and the mass spectra of the produced OA was quite similar to the oxidized OA mass spectra reported during winter in urban areas. Furthermore, good correlation was found for the OA mass spectra between the ambient-derived emissions in this study and the nocturnal aged laboratory-derived biomass burning emissions from previous work. Concentrations of NO3 radicals as high as 25 ppt (parts per trillion) were measured in the perturbed chamber, with an accompanying production of 0.1–3.2 µg m−3 of organic nitrate in the aerosol phase. Organic nitrate represented approximately 10 % of the mass of the secondary OA formed. These results strongly indicate that the OA in biomass burning plumes can chemically evolve rapidly even during wintertime periods with low photochemical activity.
Biogenic volatile organic compounds (BVOCs) are intensely
emitted by forests and crops into the atmosphere. During the night, they
react very rapidly with the nitrate radical (NO3), leading to the
...formation of a variety of functionalized products including organic nitrates
and to large amounts of secondary organic aerosols (SOAs). Organic nitrates
(ONs) have been shown not only to play a key role in the transport of reactive
nitrogen and consequently in the ozone budget but also to be important
components of the total organic-aerosol mass, while SOAs are known to play a direct
and indirect role in the climate. However, the reactivity of BVOCs with
NO3 remains poorly studied. The aim of this work is to provide new
kinetic and mechanistic data for two monoterpenes (C10H16),
α- and γ-terpinene, through experiments in simulation
chambers. These two compounds, which have very similar chemical structures,
have been chosen in order not only to overcome the lack of experimental data but also to
highlight the influence of the chemical structure on the reactivity. Rate constants have been measured using both relative and absolute methods.
They were found to be (1.2±0.5)×10-10 and (2.9±1.1)×10-11 cm3 molecule−1 s−1 for α- and γ-terpinene respectively. Mechanistic studies have
also been conducted in order to identify and quantify the main reaction
products. Total organic nitrate and SOA yields have been determined. While
organic nitrate formation yields appear to be similar, SOA yields exhibit
large differences with γ-terpinene being a much more efficient
precursor of aerosols. In order to provide explanations for this difference, chemical analysis of the gas-phase products was performed at the molecular scale. Detected products allowed for proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.
The temperature and concentration dependence of secondary organic aerosol (SOA) yields has been investigated for the first time for the photooxidation of n-dodecane (C12H26) in the presence of NOx in ...the CESAM chamber (French acronym for "Chamber for Atmospheric Multiphase Experimental Simulation"). Experiments were performed with and without seed aerosol between 283 and 304.5 K. In order to quantify the SOA yields, a new parametrization is proposed to account for organic vapor loss to the chamber walls. Deposition processes were found to impact the aerosol yields by a factor from 1.3 to 1.8 between the lowest and the highest value. As with other photooxidation systems, experiments performed without seed and at low concentration of oxidant showed a lower SOA yield than other seeded experiments. Temperature did not significantly influence SOA formation in this study. This unforeseen behavior indicates that the SOA is dominated by sufficiently low volatility products for which a change in their partitioning due to temperature would not significantly affect the condensed quantities.
Multifunctional organic nitrates, including carbonyl nitrates, are important
species formed in NOx-rich atmospheres by the degradation of volatile organic compounds (VOCs). These
compounds have been ...shown to play a key role in the transport of reactive
nitrogen and, consequently, in the ozone budget; they are also known to be important
components of the total organic aerosol. However, very little is known about
their reactivity in both the gas and condensed phases. Following a previous
study that we published on the gas-phase reactivity of α-nitrooxy
ketones, the photolysis and reaction with OH radicals of
4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone (which are a β-nitrooxy ketone and γ-nitrooxy ketone, respectively) were investigated for the
first time in simulation chambers. The photolysis frequencies were directly
measured in the CESAM chamber, which is equipped with a very realistic
irradiation system. The jnitrate/jNO2 ratios were found to be (5.9±0.9)×10-3 for 4-nitrooxy-2-butanone and (3.2±0.9)×10-3 for 5-nitrooxy-2-pentanone under our experimental
conditions. From these results, it was estimated that ambient photolysis
frequencies calculated for typical tropospheric irradiation conditions
corresponding to the 1 July at noon at 40∘ N (overhead ozone column of 300 and albedo of 0.1) are (6.1±0.9)×10-5 s−1 and (3.3±0.9)×10-5 s−1 for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively.
These results demonstrate that photolysis is a very efficient sink for these
compounds with atmospheric lifetimes of few hours. They also suggest that,
similarly to α-nitrooxy ketones, β-nitrooxy ketones have
enhanced UV absorption cross sections and quantum yields equal to or close to
unity and that γ-nitrooxy ketones have a lower enhancement of cross
sections, which can easily be explained by the larger distance between the
two chromophore groups. Thanks to a product study, the branching ratio between
the two possible photodissociation pathways is also proposed. Rate
constants for the reaction with OH radicals were found to be (2.9±1.0)×10-12 and (3.3±0.9)×10-12 cm3 molecule−1 s−1,
respectively. These experimental data are in good agreement with rate
constants estimated by the structure–activity relationship (SAR) of Kwok and Atkinson (1995) when using the
parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl
nitrates. Comparison with photolysis rates suggests that the OH-initiated
oxidation of carbonyl nitrates is a less efficient sink than
photodissociation but is not negligible in polluted areas.
The density functional theory with the BH&HLYP functional has been used in this work to clarify discrepancies found in the literature about the effect of the increasing carbon chain on the reactivity ...of trans-2-alkenals from acrolein (C3) to trans-2-octenal (C8) with nitrate radical. In this work, it was found that (i) the alkyl chain length of the unsaturated aldehydes has little or no influence on the NO3 reaction rate coefficients (ii) the abstraction of the aldehydic hydrogen from the alkenal is always dominant (83% for trans-2-butanal to trans-2-octenal). The addition channel, which mainly concerns the β addition, has a small influence (17% of the total reaction for the whole series). These results are in good agreement with the experimental studies performed by Zhao et al. in 2011 and by Kerdouci et al. in 2012. All these findings will be useful to complete or improve structure–activity relationships developed to predict the reactivity of NO3 radicals with organic compounds.
In this work is presented an extension and an update of a recently published structure–activity relationship (SAR) for the prediction of rate constants for gas-phase reactions of VOCs with NO3 ...radicals (See previous version in Kerdouci et al., 2011). Such predictive tools are very useful to describe the reactivity of organic compounds in atmospheric models. This SAR is constructed on the group-additivity method and is based on a wide kinetic database for 185 organic compounds. In addition to alkanes, alkenes and saturated and unsaturated oxygenated species already included in the first version of this SAR, this extended version comprises now aldehydes and unsaturated aldehydes. Indeed, since then, new kinetic studies have been performed for alkenals which allow the parameterization of this class of compounds. In addition, since new rate constants have been measured for unsaturated ethers, the parameterization of this family of compounds has been completed. Finally, this new version of the SAR shows very good predictive capabilities with more than 90% of the experimental rate coefficients being reproduced within a factor of two.
•Update and extension to aldehydes of an existing structure–activity relationship.•A group-additivity method has been used.•Good predictive capabilities.•90% of the experimental rate coefficients is reproduced within a factor of 2.
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