The oxidation of sabinene by the hydroxyl radical (OH)
and ozone (O3) was investigated under atmospherically relevant
conditions in the atmospheric simulation chamber SAPHIR (Simulation of
...Atmospheric Photochemistry In a Large Reaction Chamber) at Forschungszentrum
Jülich, Germany. The rate coefficients of the reactions of sabinene with
OH and with O3 were determined. The temperature dependence between 284 to 340 K of the rate coefficient of the reaction of sabinene with OH,
kSAB+OH, was measured for the first time using an OH reactivity
instrument, resulting in an Arrhenius expression of (1.67 ± 0.16) × 10−11 × exp((575 ± 30)/T) cm3 s−1. The values agree with those determined in chamber experiments in
this work and reported in the literature for ∼ 298 K within
the uncertainties of measurements. The ozonolysis reaction rate coefficient
of sabinene (kSAB+O3) determined in chamber experiments at a temperature
of (278 ± 2) K is (3.4 ± 0.8) × 10−17 cm3 s−1, which is 58 % lower than the value reported in the literature
for room temperature. The measurement of products from the oxidation of
sabinene by OH resulted in an acetone yield of (21 ± 15) %, a
formaldehyde yield of (46 ± 25) %, and a sabinaketone yield of
(18 ± 16) %. All yields determined in the chamber experiments agree
well with values from previous laboratory studies within their
uncertainties. In addition, the formaldehyde yield determined in this study
is consistent with that predicted by the sabinene OH-oxidation mechanism
which was devised from quantum chemical calculations by Wang and Wang (2018), whereas the acetone yield is about 15 % higher than that
predicted by the mechanism. In the ozonolysis experiments, the analysis of
product measurements results in an acetone yield of (5 ± 2) %, a
formaldehyde yield of (48 ± 15) %, a sabinaketone yield of
(31 ± 15) %, and an OH radical yield of (26 ± 29) %. The OH
radical yield is lower than expected from the theoretical mechanism in Wang
and Wang (2017), but the value still agrees within the uncertainty. An
analysis of the chemical budget of OH radicals was performed for the chamber
experiments. The analysis reveals that the destruction rate of the OH radical
matches the production rate of OH, suggesting that there is no significant
missing OH source for example from isomerization reactions of peroxy
radicals for the experimental conditions in this work.
The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions ...for NOx mixing ratios below 2 ppbv.
Within this study, the rate constants of the reaction of Δ3-carene with OH and O3 and of the reaction of caronaldehyde with OH were determined to be (8.0±0.5)×10-11 cm3 s−1 at 304 K, (4.4±0.2)×10-17 cm3 s−1 at 300 K and (4.6±1.6)×10-11 cm3 s−1 at 300 K, in agreement with previously published values.
The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be 0.30±0.05 and 0.06±0.02, respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02. The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Δ3-carene.
Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx=OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the chamber experiments.
In an OH-free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.
The oxidation of Î.sup.3 -carene and one of its main oxidation products, caronaldehyde, by the OH radical and O.sub.3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric ...conditions for NO.sub.x mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Î.sup.3 -carene with OH and O.sub.3 and of the reaction of caronaldehyde with OH were determined to be (8.0±0.5)x10-11 cm.sup.3 s.sup.-1 at 304 K, (4.4±0.2)x10-17 cm.sup.3 s.sup.-1 at 300 K and (4.6±1.6)x10-11 cm.sup.3 s.sup.-1 at 300 K, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Î.sup.3 -carene were determined to be 0.30±0.05 and 0.06±0.02, respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate (RONO.sub.2) yield from the reaction of NO with RO.sub.2 derived from Î.sup.3 -carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species (NO.sub.y) in the SAPHIR chamber. The RONO.sub.2 yield of the reaction of NO with RO.sub.2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02. The organic nitrate yields of Î.sup.3 -carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Î.sup.3 -carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx=OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Î.sup.3 -carene for conditions of the chamber experiments. In an OH-free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.
The gas-phase reaction of isoprene with the nitrate radical (NO3) was investigated in experiments in the outdoor SAPHIR chamber under atmospherically relevant conditions specifically with respect to ...the chemical lifetime and fate of nitrato-organic peroxy radicals (RO2). Observations of organic products were compared to concentrations expected from different chemical mechanisms: (1) the Master Chemical Mechanism, which simplifies the NO3 isoprene chemistry by only considering one RO2 isomer; (2) the chemical mechanism derived from experiments in the Caltech chamber, which considers different RO2 isomers; and (3) the FZJ-NO3 isoprene mechanism derived from quantum chemical calculations, which in addition to the Caltech mechanism includes equilibrium reactions of RO2 isomers, unimolecular reactions of nitrate RO2 radicals and epoxidation reactions of nitrate alkoxy radicals. Measurements using mass spectrometer instruments give evidence that the new reactions pathways predicted by quantum chemical calculations play a role in the NO3 oxidation of isoprene. Hydroperoxy aldehyde (HPALD) species, which are specific to unimolecular reactions of nitrate RO2, were detected even in the presence of an OH scavenger, excluding the possibility that concurrent oxidation by hydroxyl radicals (OH) is responsible for their formation. In addition, ion signals at masses that can be attributed to epoxy compounds, which are specific to the epoxidation reaction of nitrate alkoxy radicals, were detected. Measurements of methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations confirm that the decomposition of nitrate alkoxy radicals implemented in the Caltech mechanism cannot compete with the ring-closure reactions predicted by quantum chemical calculations. The validity of the FZJ-NO3 isoprene mechanism is further supported by a good agreement between measured and simulated hydroxyl radical (OH) reactivity. Nevertheless, the FZJ-NO3 isoprene mechanism needs further investigations with respect to the absolute importance of unimolecular reactions of nitrate RO2 and epoxidation reactions of nitrate alkoxy radicals. Absolute concentrations of specific organic nitrates such as nitrate hydroperoxides would be required to experimentally determine product yields and branching ratios of reactions but could not be measured in the chamber experiments due to the lack of calibration standards for these compounds. The temporal evolution of mass traces attributed to product species such as nitrate hydroperoxides, nitrate carbonyl and nitrate alcohols as well as hydroperoxy aldehydes observed by the mass spectrometer instruments demonstrates that further oxidation by the nitrate radical and ozone at atmospheric concentrations is small on the timescale of one night (12 h) for typical oxidant concentrations. However, oxidation by hydroxyl radicals present at night and potentially also produced from the decomposition of nitrate alkoxy radicals can contribute to their nocturnal chemical loss.
The oxidation of limonene by the hydroxyl (OH) radical
and ozone (O3) was investigated in the atmospheric simulation chamber
SAPHIR (Simulation of Atmospheric
PHotochemistry In a large Reaction ...Chamber) in experiments performed at different nitric oxide (NO) mixing ratios from nearly 0 up to 10 ppbv. For the experiments dominated by OH
oxidation, the formaldehyde (HCHO) yield was experimentally determined and found to be (12 ± 3), (13 ± 3), and (32 ± 5) % for
experiments with low (∼ 0.1 ppbv), medium (∼ 0.3 ppbv), and high NO (5 to 10 ppbv), respectively. The yield in an
ozonolysis-only experiment was (10 ± 1) %, which agrees with previous
laboratory studies. The experimental yield of the first-generation organic nitrates from limonene–OH oxidation is calculated as (34 ± 5) %,
about 11 % higher than the value in the Master Chemical Mechanism (MCM),
which is derived from structure–activity relationships (SARs). Time series of measured radicals, trace-gas concentrations, and OH reactivity are compared
to results from zero-dimensional chemical box model calculations applying
MCM v3.3.1. Modeled OH reactivity is 5 to 10 s−1 (25 % to 33 % of the OH reactivity at the start of the experiment) higher than measured
values at the end of the experiments under all chemical conditions investigated, suggesting either that there are unaccounted loss processes of
limonene oxidation products or that products are less reactive toward OH. In
addition, model calculations underestimate measured hydroperoxyl radical
(HO2) concentrations by 20 % to 90 % and overestimate organic
peroxyl radical (RO2) concentrations by 50 % to 300 %. The largest deviations are found in low-NO experiments and in the ozonolysis experiment.
An OH radical budget analysis, which uses only measured quantities, shows
that the budget is closed in most of the experiments. A similar budget
analysis for RO2 radicals suggests that an additional RO2 loss
rate constant of about (1–6) × 10−2 s−1 for
first-generation RO2 is required to match the measured RO2
concentrations in all experiments. Sensitivity model runs indicate that
additional reactions converting RO2 to HO2 at a rate constant of
about (1.7–3.0) × 10−2 s−1 would improve the
model–measurement agreement of NOx, HO2, and RO2 concentrations and OH reactivity. Reaction pathways that could lead to the production of
additional OH and HO2 are discussed, which include isomerization reactions of RO2 from the oxidation of limonene, different branching
ratios for the reaction of RO2 with HO2, and a faster rate
constant for RO2 recombination reactions. As the exact chemical
mechanisms of the additional HO2 and OH sources could not be
identified, further work needs to focus on quantifying organic product
species and organic peroxy radicals from limonene oxidation.
The photooxidation of the most abundant monoterpene, α-pinene, by the hydroxyl radical (OH) was investigated at atmospheric concentrations in the atmospheric simulation chamber SAPHIR. Concentrations ...of nitric oxide (NO) were below 120 pptv. Yields of organic oxidation products are determined from measured time series giving values of 0.11±0.05, 0.19±0.06, and 0.05±0.03 for formaldehyde, acetone, and pinonaldehyde, respectively. The pinonaldehyde yield is at the low side of yields measured in previous laboratory studies, ranging from 0.06 to 0.87. These studies were mostly performed at reactant concentrations much higher than observed in the atmosphere. Time series of measured radical and trace-gas concentrations are compared to results from model calculations applying the Master Chemical Mechanism (MCM) 3.3.1. The model predicts pinonaldehyde mixing ratios that are at least a factor of 4 higher than measured values. At the same time, modeled hydroxyl and hydroperoxy (HO2) radical concentrations are approximately 25 % lower than measured values. Vereecken et al. (2007) suggested a shift of the initial organic peroxy radical (RO2) distribution towards RO2 species that do not yield pinonaldehyde but produce other organic products. Implementing these modifications reduces the model–measurement gap of pinonaldehyde by 20 % and also improves the agreement in modeled and measured radical concentrations by 10 %. However, the chemical oxidation mechanism needs further adjustment to explain observed radical and pinonaldehyde concentrations. This could be achieved by adjusting the initial RO2 distribution, but could also be done by implementing alternative reaction channels of RO2 species that currently lead to the formation of pinonaldehyde in the model.
The reactions of biogenic volatile organic compounds (BVOC) with the nitrate radicals (NO
) are major night-time sources of organic nitrates and secondary organic aerosols (SOA) in regions influenced ...by BVOC and anthropogenic emissions. In this study, the formation of gas-phase highly oxygenated organic molecules-organic nitrates (HOM-ON) from NO
-initiated oxidation of a representative monoterpene, β-pinene, was investigated in the SAPHIR chamber (Simulation of Atmosphere PHotochemistry In a large Reaction chamber). Six monomer (C = 7-10, N = 1-2, O = 6-16) and five accretion product (C = 17-20, N = 2-4, O = 9-22) families were identified and further classified into first- or second-generation products based on their temporal behavior. The time lag observed in the peak concentrations between peroxy radicals containing odd and even number of oxygen atoms, as well as between radicals and their corresponding termination products, provided constraints on the HOM-ON formation mechanism. The HOM-ON formation can be explained by unimolecular or bimolecular reactions of peroxy radicals. A dominant portion of carbonylnitrates in HOM-ON was detected, highlighting the significance of unimolecular termination reactions by intramolecular H-shift for the formation of HOM-ON. A mean molar yield of HOM-ON was estimated to be 4.8% (-2.6%/+5.6%), suggesting significant HOM-ON contributions to the SOA formation.
Ambient measurements of nitryl chloride (ClNO2) were
performed at a rural site in Germany, covering three periods in winter,
summer, and autumn 2019, as part of the JULIAC campaign (Jülich
...Atmospheric Chemistry Project) that aimed to understand the
photochemical processes in air masses typical of midwestern Europe.
Measurements were conducted at 50 m aboveground, which was mainly located
in the nocturnal boundary layer and thus uncoupled from local surface
emissions. ClNO2 is produced at night by the heterogeneous reaction of
dinitrogen pentoxide (N2O5) on chloride (Cl−) that contains
aerosol. Its photolysis during the day is of general interest, as it produces chlorine (Cl) atoms that react with different atmospheric trace gases to form radicals. The highest-observed ClNO2 mixing ratio
was 1.6 ppbv (parts per billion by volume; 15 min average) during the night of 20 September. Air masses reaching the measurement site either originated from long-range transport from the southwest and had an oceanic influence or circulated in the nearby region and were influenced by anthropogenic activities. Nocturnal maximum ClNO2 mixing ratios were around 0.2 ppbv if originating from long-range transport in nearly all seasons, while the values were higher, ranging from 0.4 to 0.6 ppbv for regionally influenced air. The chemical composition of long-range transported air was similar in all investigated seasons, while the regional air exhibited larger differences between the seasons. The N2O5 necessary for ClNO2 formation comes from the reaction of nitrate radicals (NO3) with nitrogen dioxide (NO2), where NO3
itself is formed by a reaction of NO2 with ozone (O3). Measured
concentrations of ClNO2, NO2, and O3 were used to quantify
ClNO2 production efficiencies, i.e., the yield of ClNO2 formation
per NO3 radical formed, and a box model was used to examine the
idealized dependence of ClNO2 on the observed nocturnal O3 and
NO2 concentrations. Results indicate that ClNO2 production
efficiency was most sensitive to the availability of NO2 rather than
that of O3 and increased with decreasing temperature. The average
ClNO2 production efficiency was highest in February and September, with values of 18 %, and was lowest in December, with values of 3 %. The average ClNO2 production efficiencies were in the range of 3 % and 6 % from August to November for air masses originating from long-range transportation. These numbers are at the high end of values reported in the literature, indicating the importance of ClNO2 chemistry in rural environments in midwestern Europe.
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