Pinonic Acid Research Articles

Pinonic Acid Derivatives Containing Thiourea Motif: Promising Antifungal Lead Compound Targeting Cellular Barrier of Colletotrichum fructicola.

In order to explore novel antifungal lead compounds from plant essential oil, thirty-two pinonic acid derivatives containing thiourea groups were designed and synthesized using α-pinene as a raw material. One of these pinonic acid derivatives compound 3a exhibited noteworthy in vitro antifungal activity against Colletotrichum fructicola (EC50 = 9.22 mg/L), which was comparable to that of the positive control kresoxim-methyl (EC50 = 9.69 mg/L). Structure-activity relationship (SAR) studies demonstrated that the introduction of thiourea groups, F atoms, and Cl atoms into the structure of pinonic acid derivatives significantly improved their antifungal activity. The in vivo antifungal test revealed that compound 3a could effectively control pear anthracnose. It also proved that compound 3a showed low acute oral toxicity to honeybees (LD50 > 100 μg/bee) and low or no cytotoxicity to LO2 and HEK293 cell lines. The preliminary mechanism of action studies revealed that compound 3a caused mycelium deformity, increased cell membrane permeability, blocked the normal process of phospholipase C on the cell membrane, and reduced mycelium protein content. The results of molecular docking studies demonstrated the stable binding of compound 3a to phospholipase C and chitin synthetase. This study suggested that compound 3a could be used as a promising lead compound for the development of novel antifungal agents targeting the cellular barrier of C. fructicola.

Oxidation properties and thermal hazard of pinane

Although pinane has a wide range of uses, there are no reports on the safety of pinane oxidation. The thermal oxidation properties of pinane were investigated through MCPVT. The primary oxidation products of pinane were separated and structurally characterised, and its decomposition properties were assessed by MCPVT and DSC. The results showed that pinane had an initial oxygen uptake temperature of 123.5 °C and exploded when the temperature rose to 132.7 °C. Pinane autoxidised at 110 °C for 9 h formed a high level of peroxide (81.18 mmol/kg) with an activation energy of 138.77 kJ/mol. The oxidation of pinane occurs mainly at the tertiary carbon atom attached to the methyl group, and the main peroxide produced is pinane hydroperoxide (PHP). PHP has an exothermic onset temperature (Tonset), a heat of decomposition (QDSC) and an activation energy of decomposition of 114.6 °C, 1878.0 J/g and 109.4 kJ/mol respectively, which should classify it as a hazardous substance. PHP has a lower activation energy than pinane and is the determining factor for the safety of the pinane oxidation reaction. The products of thermal runaway of pinane are relatively complex and consist mainly of 1-(2, 2-dimethyl-3-ethylcyclobutyl) ethanone, nopinone, 2, 3-pinanediol and pinonic acid.

Relative humidity-dependent evolution of molecular composition of α-pinene secondary organic aerosol upon heterogeneous oxidation by hydroxyl radicals

Heterogeneous oxidation by gas-phase oxidants is an important chemical transformation pathway of secondary organic aerosol (SOA) and plays an important role in controlling the abundance, properties, as well as climate and health impacts of aerosols. However, our knowledge on this heterogeneous chemistry remains inadequate. In this study, the heterogeneous oxidation of α-pinene ozonolysis SOA by hydroxyl (OH) radicals was investigated under both low and high relative humidity (RH) conditions, with an emphasis on the evolution of molecular composition of SOA and its RH dependence. It is found that the heterogeneous oxidation of SOA at an OH exposure level equivalent to 12 hr of atmospheric aging leads to particle mass loss of 60% at 25% RH and 95% at 90% RH. The heterogeneous oxidation strongly changes the molecular composition of SOA. The dimer-to-monomer signal ratios increase dramatically with rising OH exposure, in particular under high RH conditions, suggesting that aerosol water stimulates the reaction of monomers with OH radicals more than that of dimers. In addition, the typical SOA tracer compounds such as pinic acid, pinonic acid, hydroxy pinonic acid and dimer esters (e.g., C17H26O8 and C19H28O7) have lifetimes of several hours against heterogeneous OH oxidation under typical atmospheric conditions, which highlights the need for the consideration of their heterogeneous loss in the estimation of monoterpene SOA concentrations using tracer-based methods. Our study sheds lights on the heterogeneous oxidation chemistry of monoterpene SOA and would help to understand their evolution and impacts in the atmosphere.

Molecular identification of organic acid molecules from α-pinene ozonolysis

Oxidized organic molecules from ozonolysis of α-pinene are believed to participate in atmospheric new particle formation in forest regions. However, the detailed process of nucleation originated from α-pinene ozonolysis remains unclear. In this study, an atmospheric pressure interface time-of-flight mass spectrometer coupled with a planar differential mobility analyzer (DMA-MS) was applied to investigate the gas-phase reaction of α-pinene and ozone. Ion mobility and mass to charge ratio of the oxidized molecules were simultaneously measured. The ion mobility distribution of these oxidation products highlighted three mobility diameter ranges: 0.89–0.99 nm, 1.16–1.24 nm and 1.31–1.38 nm, where the dominating molecules were CH2O2, C7-10H10-20O3-7 and C19-20H30-32O6-9, respectively. Combining the DMA-MS measurements, quantum chemistry calculations, and ion mobility modeling, the dominant monomer (C10H16O3) was confirmed as pinonic acid while the primary dimer (C20H32O6) was considered as pinonic acid cluster ((C10H16O3)2). Considering the yield of pinonic acid produced from α-pinene ozonolysis (2–4%), (C10H16O3)2 potentially accounts for part of the nocturnal C20 dimers and ungrowable sub-2-nm particles in forests. Our work provides a new method to facilitate the understanding of atmospheric nucleation and initial growth.

Characterization of chemical components of fresh and aged aerosol from vehicle exhaust emissions in Hong Kong

The chemical properties of fresh and aged aerosol emitted during controlled vehicular exhaust emissions were characterized in the analysis. Pyrene (10417.1 ± 534.9 ng kg−1) is the most abundant of all analyzed compounds in total fresh emission and succinic acid (57359.8 ± 4000.3 ng kg−1) is for the total aged emission. The fresh emission factors (EFfresh) of all compounds in the n-alkanes group demonstrate higher average emissions for the two vehicles with EURO 3 standard compared to the other vehicles. The EFfresh for benzo [a]pyrene is in descending order: G1 (183.1 ± 144.7 ng kg−1) > G3 (103.4 ± 60.1 ng kg−1) > G4 (91.2 ± 80.1 ng kg−1) > G2 (88.6 ± 93.9 ng kg−1). Aged/fresh (A/F) emission ratios (>20) confirmed that these diacid compounds are generated by the photooxidation of primary pollutants that emitted from gasoline combustions. High A/F ratios (>200) in phthalic acid, isophthalic acid and terephthalic acid under idling mode imply relatively more intense photochemical reactions for their productions compared with other chemical groups. Strong positive correlations (r > 0.6) were observed between the degradation of toluene and formations of pinonic acid, succinic acid, adipic acid, terephthalic acid, glutaric acid and citramalic acid after the aging process, suggesting possible photooxidation of toluene that can lead to secondary organic aerosol (SOA) formation in the urban atmosphere. The findings demonstrate that vehicle emission standards for pollution in relation to the change of particulate matter chemical compositions and SOA formations. The results warrant a need for regulated reformulation for such vehicles.

Seasonal characteristics of biogenic secondary organic aerosol tracers in a deciduous broadleaf forest in northern Japan

We collected total suspended particulate (TSP) samples from January 2010 to December 2010 at Sapporo deciduous forest to understand the oxidation processes of biogenic volatile organic compounds (BVOCs). The gas chromatography-mass spectrometric technique was applied to determine biogenic secondary organic aerosols (BSOAs) in the TSP samples. We found the predominance of the isoprene SOA (iSOA) tracers (20.6 ng m−3) followed by α/β-pinene SOA (pSOA) tracers (8.25 ng m−3) and β-caryophyllene SOA (cSOA) tracer (1.53 ng m−3) in the forest aerosols. The results showed large isoprene fluxes and relatively high levels of oxidants in the forest atmosphere. The iSOA and pSOA tracers showed a clear seasonal trend with summer and autumn maxima and winter and spring minima. Their seasonal trends were mainly controlled by BVOCs emission from the local broadleaf deciduous forest. Additionally, the regional level of isoprene emissions from the oceanic sources may also be contributed during summertime aerosols. cSOA tracer showed high concentrations in the winter and spring, possibly due to an additional contribution of biomass burning (BB) aerosols from the local or regional BB activities. The biogenic secondary organic carbon (BSOC) was contributed mainly by the oxidation products of isoprene (136 ngC m−3) followed by β-caryophyllene (63.0 ngC m−3) and α/β-pinene (35.9 ngC m−3). The mass concentration ratio (0.92) of pinonic acid + pinic acid and 3-methyl-1,2,3-butanetricarboxylic acid ((PNA + PA)/3-MBTCA) indicates the photochemical transformation of first-generation oxidation products to the higher generation oxidation products. The average ratios of isoprene to α/β-pinene (1.64) and β-caryophyllene (18.6) oxidation products suggested a large difference in the emissions of isoprene and α/β-pinene compared to β-caryophyllene. The cSOA tracers in the forest aerosols are also contributed by BB during the winter and spring. Positive matrix factorization analyses of the BSOA tracers confirmed that organic aerosols of deciduous forests are mostly related to isoprene emissions. This study suggests that isoprene is a more significant precursor for the BSOA than α/β-pinene and β-caryophyllene in a broadleaf deciduous forest.

Peroxy Radical and Product Formation in the Gas-Phase Ozonolysis of α-Pinene under Near-Atmospheric Conditions: Occurrence of an Additional Series of Peroxy Radicals O,O-C10H15O(O2)yO2 with y = 1-3.

Ozonolysis of α-pinene, C10H16, and other monoterpenes is considered to be one of the important chemical process in the atmosphere leading to condensable vapors, which are relevant to aerosol formation and, finally, for Earth's radiation budget. The formation of peroxy (RO2) radicals, O,O-C10H15(O2)xO2 with x = 0-3, and closed-shell products has been probed from the ozonolysis of α-pinene for close to atmospheric reaction conditions. (The "O,O" in the chemical formulas indicates the two carbonyl groups formed in the ozonolysis.) An additional series of RO2 radicals, O,O-C10H15O(O2)yO2 with y = 1-3, emerged in the presence of NO additions of (1.7-50) × 109 molecules cm-3, whose formation can be explained via different processes starting from alkoxy (RO) radicals, such as the RO-driven autoxidation. The main closed-shell product is a substance with the composition C10H16O3, probably pinonic acid, obtained with a molar yield (lower limit) of 0.26 independent of NO. Total molar product yields accounted for up to 0.71 indicating reasonable detection sensitivity of the analytical technique applied. For the isomeric O,O-C10H15O2 radicals, an average rate coefficient k(RO2 + NO) = (1.5 ± 0.3) × 10-11 cm3 molecule-1 s-1 at 295 ± 2 K was determined. Product analysis showed a lowering in the formation of highly oxygenated organic molecules (HOMs) by a factor of ∼2.2 when adding 5 × 1010 molecules cm-3 of NO. The comparison with former results revealed that total HOM suppression by NO in the α-pinene ozonolysis is slightly stronger than in the OH + α-pinene reaction.

Isomer-Resolved Mobility-Mass Analysis of α-Pinene Ozonolysis Products.

Highly oxygenated organic molecules (HOMs) are important sources of atmospheric aerosols. Resolving the molecular-level formation mechanisms of these HOMs from freshly emitted hydrocarbons improves the understanding of aerosol properties and their influence on the climate. In this study, we measure the electrical mobility and mass-to-charge ratio of α-pinene oxidation products using a secondary electrospray-differential mobility analyzer-mass spectrometer (SESI-DMA-MS). The mass-mobility spectrum of the oxidation products is measured with seven different reagent ions generated by the electrospray. We analyzed the mobility-mass spectra of the oxidation products C9–10H14–18O2–6. Our results show that acetate and chloride yield the highest charging efficiencies. Analysis of the mobility spectra suggests that the clusters have 1–5 isomeric structures (i.e., ion-molecule cluster structures with distinct mobilities), and the number is affected by the reagent ion. Most of the isomers are likely cluster isomers originating from binding of the reagent ion to different sites of the molecule. By comparing the number of observed isomers and measured mobilities and collision cross sections between standard pinanediol and pinonic acid to the values observed for C10H18O2 and C10H16O3 produced from oxidation of α-pinene, we confirm that pinanediol and pinonic acid are the only isomers for these elemental compositions in our experimental conditions. Our study shows that the SESI-DMA-MS produces new information from the first steps of oxidation of α-pinene.

Spatial and seasonal variations of primary and secondary organic aerosols at urban areas and continental background site of China: Ambient levels, size distribution, and sources

Organic aerosols are important constituents of particulate matter (PM) in the atmosphere, however, the studies on their size distribution, particularly for special primary and secondary organic aerosols (POA, SOA), are relatively limited. In this work, the size-segregated PM was collected from five megacities (Shanghai, Guangzhou, Xi’an, Chengdu, Urumqi) and a continental background site (Qinghai Lake, Tibetan Plateau) of China during 2012–2014. Special POA (plant wax n-alkanes, fossil fuel n-alkanes, PAHs, levoglucosan, and trehalose) and biogenic SOA (BSOA, i.e. isoprene oxidants, monoterpene oxidants, and β-caryophyllenic acid) in PM were measured using gas chromatography/mass spectrometry. n-Alkanes were highest in autumn in the Southeast of China and highest in summer in the Northwest of China during the four seasons. PAHs and levoglucosan were higher in the cold season, mainly influenced by residential heating. Isoprene and monoterpene oxidants were higher in the warm season, while β-caryophyllenic acid was found to be much higher in cold seasons. n-Alkanes showed a monomodal distribution, with a peak at the fine mode (<1.1 µm). PAHs and levoglucosan were characterized by an accumulation mode, revealing the peak at <1.1 µm. However, only trehalosedisplayed coarse mode at the six sites, peaking at a size of 3.3–9.0 µm, because it was mostly derived frombiota in desert regions. Isoprene oxidants including 2-methylglyceric acid, 2-methyltetrols, and C5-alkene triols exhibited a unimodal size distribution pattern with a peak in the fine mode. Monoterpene oxidants such as cis-pinic acid, pinonic acid, 3-hydroxyglutaric acid, and 3-methyl-1,2,3-butanetricarboxylic acid exhibited a bimodal size distribution pattern in the whole sampling time, peaking at the size range of <1.1 µm and 3.3–9.0 µm, respectively. Only β-caryophyllenic acid displayed a fine mode at the six sites during the whole sampling time. These findings can be used to support research into the origin and formation mechanisms of POA and BSOA.

LED-based solar simulator to study photochemistry over a wide temperature range in the large simulation chamber AIDA

Abstract. A light source has been built at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) simulation chamber at the Karlsruhe Institute of Technology, simulating solar radiation at ground level. Instead of full spectra light sources, it uses a combination of LEDs with a narrow emission spectrum, resulting in a combined spectrum similar to the solar spectrum between 300 and 530 nm. The use of LEDs leads to an energy-efficient, robust and versatile illumination concept. The light source can be used over a wide temperature range down to −90 ∘C and is adjustable in intensity and spectral width as well as easily adjustable to new technological developments or scientific needs. Characterization of the illumination conditions shows a vertical intensity gradient in the chamber. The integral intensity corresponds to a NO2 photolysis frequency j(NO2) of (1.58±0.21(1σ))×10-3 s−1 for temperatures between 213 and 295 K. At constant temperature, the light intensity is stable within ±1 %. While the emissions of the different LEDs change with temperature, they can be adjusted, and thus it is possible to adapt the spectrum for different temperatures. Although the illumination of the simulation chamber leads to an increase of 0.7 K h−1 of the mean gas temperature, it is possible to perform experiments with aqueous droplets at relative humidities up to ≤95 % and also above water or ice saturation with corresponding clouds. Additionally, temperature- and wavelength-dependent photolysis experiments with 2,3-pentanedione have been conducted. The photolysis of 2,3-pentanedione occurs mainly between 400 and 460 nm, resulting in a mean photolysis frequency of (1.03±0.15)×10-4 s−1 independent of temperature in the range 213–298 K with a quantum yield of 0.36±0.04. In contrast, the yield of the two main photolysis products, acetaldehyde and formaldehyde, decreases with temperature. Furthermore, the light source was applied to study the photochemistry of aerosol particles. For the atmospheric brown carbon proxy compound 3,5-diacetyl-2,4,6-trimethyl-1,4-dihydropyridine, photochemical reaction products were identified. In aerosol particles containing iron oxalate as a photosensitizer, the photosensitized degradation of organic acids (pinic and pinonic acid) was studied. Although the light source only generates about one-third of the maximum solar irradiation at ground level at Karlsruhe (49.007∘ N, 8.404∘ E; 12:00 UTC+2) on a clear summer day with a substantial intensity gradient throughout the simulation chamber, it could be shown that this type of light source allows reproducible experiments over a wide range of simulated atmospheric conditions and with a large flexibility and control of the irradiation spectrum.

Modeling Secondary Organic Aerosol Tracers and Tracer-to-SOA Ratios for Monoterpenes and Sesquiterpenes Using a Chemical Transport Model.

The community multiscale air quality (CMAQ) model was modified to simulate secondary organic aerosol (SOA) formation from five explicit (α-pinene, β-pinene, d-limonene, Δ3-carene, and sabinene) and one lumped monoterpene (MT) species and sesquiterpenes (SQTs). The contribution of each oxidation pathway [including OH, O3, NO3, and O(3P)] was explicitly tracked in the SOA module. Three MT SOA tracers (pinic acid, PA; pinonic acid, PNA; and 3-methyl-1,2,3-butanetricarboxylic acid, MBTCA) and one SQT SOA tracer (β-caryophyllinic acid, BCARYA) were modeled to assess the tracer-to-SOA ratios (fSOA) for ambient SOA estimation. Good model performance for BCARYA and MBTCA and reasonable agreement between model predictions and observations of PA and PNA were achieved. The modeled daily fSOA showed significant variations, suggesting that using the chamber-derived constant fSOA could lead to large errors in estimating terpene SOA. Among the four tracers, MBTCA and BCARYA were more appropriate for tracking MT and SQT SOA due to their nonvolatility. Their fSOA values mainly depend on the organic aerosol loading and could be approximated using simple power-law equations. In addition, equations directly linking the tracer concentrations to the corresponding SOA concentrations were proposed and could lead to good SOA estimations. This work provides new insights into the formation of the key MT and SQT SOA tracers and would allow better assessments of the biogenic emissions to regional and global aerosol burden.

Importance of secondary organic aerosol formation of &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-pinene, limonene, and &amp;lt;i&amp;gt;m&amp;lt;/i&amp;gt;-cresol comparing day- and nighttime radical chemistry

Abstract. The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate α-pinene, limonene, and m-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NO3 radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NO3 under dry conditions significantly exceeds that of the OH-radical reaction, with SOA yields of 15–30 % and 10–21 %, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. In contrast, the SOA formation potential of α-pinene with NO3 slightly exceeds that of the OH-radical reaction, independent from RH. On average, α-pinene yielded SOA with about 6–7 % from NO3 radicals and 3–4 % from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for m-cresol oxidation with OH radicals (3–9 %), with the highest yield under elevated RH (9 %), which is most likely attributable to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While α-pinene and m-cresol SOA was found to be mainly composed of water-soluble compounds, 50–68 % of nocturnal SOA and 22–39 % of daytime limonene SOA are water-insoluble. The fraction of SOA-bound peroxides which originated from α-pinene varied between 2 and 80 % as a function of RH. Furthermore, SOA from α-pinene revealed pinonic acid as the most important particle-phase constituent under day- and nighttime conditions with a fraction of 1–4 %. Other compounds detected are norpinonic acid (0.05–1.1 % mass fraction), terpenylic acid (0.1–1.1 % mass fraction), pinic acid (0.1–1.8 % mass fraction), and 3-methyl-1,2,3-tricarboxylic acid (0.05–0.5 % mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and showed almost no RH effect when formed during night.

Secondary organic aerosol markers and related polar organic compounds in summer aerosols from a sub-urban site in Athens: Size distributions, diurnal trends and source apportionment

Size-segregated aerosols (six stages with a diameter from <0.49 to >7.2 μm) were collected during daytime and nighttime in the summer of 2020 and were analyzed for dicarboxylic acids, isoprene, α/β-pinene and β-caryophyllene secondary organic aerosol (SOA) tracers, aromatic acids, hydroxy-polyacids, monocarboxylic acids and levoglucosan. The vast majority of the detected compounds presented significantly higher (p < 0.05) concentrations in fine than in coarse modes, excluding benzoic and oleic acids for which the higher fine mode than coarse mode concentrations were not significant and pinonic acid which was found at higher coarse mode concentrations. The dominant compound in the fine mode was 2-methylerythritol (mean of 213 ± 79.4 ng m−3), whereas in coarse particles palmitic acid was the most abundant (mean of 22.8 ± 9.7 ng m−3). All of the detected compounds, except for terephthalic acid, presented higher daytime concentrations, a difference that in the cases of glutaric, suberic, azelaic and pinic acids was significant (p < 0.05). The six-stage size distribution showed various patterns, with most species peaking at particles with a diameter of <1.1 μm suggesting photoxidation sources, while significant peaks at the size of 3–7.2 μm have been observed for suberic, azelaic, pinonic, benzoic, trimellitic and monocarboxylic acids. The hydroscopic growth of particles during nighttime may explain the observed decrease of the fine to coarse concentration ratio. From the employed source apportionment tools four factors where derived explaining 83.0% of total the variance including oxidation of anthropogenic volatile organic compounds (35.6%), oxidation of monoterpenes and sesquiterpenes (21.5%), isoprene's oxidation (14.1%) and photoxidation of unsaturated fatty acids (11.8%).

Contribution of Terpenes to Ozone Formation and Secondary Organic Aerosols in a Subtropical Forest Impacted by Urban Pollution

The highly reactive nature of biogenic volatile organic compounds (BVOCs) impacts the biosphere by acting as a precursor of ozone and aerosols that influence air quality and climate. Here, we assess the influence of BVOCs and their oxidation products on ozone formation and to submicron secondary organic aerosol (SOA) mass in a subtropical forest. A high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) was employed for the continuous measurement of VOCs. Isoprene, monoterpene, and sesquiterpene mixing ratios in the forest were 0.23, 0.22, and 0.03 ppb, respectively. The total ozone formation potential (OFP) of the terpenes was 12.8 μg m−3, which accounted for only 5.6% of the total OFP. Particle phase bound oxidation products were characterized using a thermal-desorption PTR-ToF-MS. Mass spectra analysis revealed the presence pinonaldehyde, pinonic, norpinonic, and pinic acid in both gas and particle phase. The overall daytime (nighttime) mixing ratio of the oxidized BVOCs in gas phases was 0.062(0.023) ppbv. On the other hand, the mean fraction of the four monoterpene oxidation products in condensed phase was estimated at 42%. Overall, the results of this study evidenced quantitatively the contribution of BVOCs to the total reactivity and SOA mass in the subtropical forest.

Interactions of sulfuric acid with common atmospheric bases and organic acids: Thermodynamics and implications to new particle formation

Interactions of the three common atmospheric bases, dimethylamine ((CH3)2NH), methylamine (CH3NH2), ammonia (NH3), all considered to be efficient stabilizers of binary clusters in the Earth's atmosphere, with H2SO4, the key atmospheric precursor, and 14 common atmospheric organic acids (COAs) (formic, acetic, oxalic, malonic, succinic, glutaric acid, adipic, benzoic, phenylacetic, pyruvic, maleic acid, malic, tartaric and pinonic acids) have been studied using the density functional theory (DFT) and composite high-accuracy G3MP2 method. The thermodynamic stability of mixed (COA)(H2SO4), (COA)(B1), (COA)(B2) and (COA)(B3) dimers and (COA)(H2SO4)(B1), (COA)(H2SO4)(B2) and (COA)(H2SO4)(B3) trimers, where B1, B2 and B3 refer to (CH3)2NH, CH3NH2 and NH3, respectively, have been investigated and their impacts on the thermodynamic stability of clusters containing H2SO4 have been studied. Our investigation shows that interactions of H2SO4 with COA, (CH3)2NH, CH3NH2 and NH3 lead to the formation of more stable mixed dimers and trimers than (H2SO4)2 and (H2SO4)2(base), respectively, and emphasize the importance of common organic species for early stages of atmospheric nucleation. We also show that although amines are generally confirmed to be more active than NH3 as stabilizers of binary clusters, in some cases mixed trimers containing NH3 are more stable thermodynamically than those containing CH3NH2. This study indicates an important role of COA, which coexist and interact with that H2SO4 and common atmospheric bases in the Earth atmosphere, in formation of stable pre-nucleation clusters and suggests that the impacts of COA on new particle formation (NPF) should be studied in further details.

Biogenic volatile organic compounds (BVOCs) reactivity related to new particle formation (NPF) over the Landes forest

Abstract Atmospheric particles play a major role in both air quality and climate change. Formation of secondary particles in the atmosphere has been observed over many different environments and is believed to provide up to half of the atmospheric cloud condensation nuclei (CCN) at a global scale. However, high uncertainties are still remaining in the description of mechanisms involved in new particle formation (NPF). Especially, more evidences of the implication of biogenic volatile organic compounds (BVOCs) in NPF from field studies are still needed. To investigate this question, two field campaigns have been set up during July 2014 and July 2015, in the French Landes forest (south west of France). Summer 2015 was characterized by a strong hydric stress, whereas summer 2014 was rainy. In 2015, frequent nocturnal NPF was observed, reaching a frequency of occurrence of ~55% of the nights, while only one event was observed in 2014. In July 2015, monoterpene mixing ratios (dominated by α- and β-pinene) were higher, mostly due to high ambient temperatures and drought. A focus was made on the 2015 field campaign, where NPF was mostly observed. The mean diurnal variation of the ratio between α- and β-pinene mixing ratios highlighted in-canopy reactivity of monoterpenes with ozone in the early night. This hypothesis was reinforced by the increasing gas phase levels of pinonaldehyde and nopinone, the main first-generation products arising from α- and β-pinene ozonolysis, at night, before NPF started. It strongly suggests that monoterpene oxidation further generated very-low volatility gases involved in NPF. This finding is also supported by the high concentrations of the SOA traditional biogenic tracers, e.g. pinic and pinonic acids, quantified in the particulate phase. The role of BVOCs in NPF is thus highlighted, as well as the importance of nighttime NPF.

Physicochemical Properties of Pinic, Pinonic, Norpinic, and Norpinonic Acids as Relevant α-Pinene Oxidation Products.

Here, the study is focused on the synthesis and determination of physicochemical properties of four α-pinene secondary organic aerosol (SOA) products: cis-pinic acid, cis-pinonic acid, cis-norpinic acid, and cis-norpinonic acid. These encompass their thermal properties, solid-liquid phase equilibria, and dissociation constant (pKa). Thermal properties, including the melting temperature, enthalpy of fusion, temperature, and enthalpy of the phase transitions, were measured with the differential scanning calorimetry technique. These SOA components exhibit relatively high melting temperatures from 364.32 K for cis-pinic acid to 440.68 K for cis-norpinic acid. The enthalpies of fusion vary from 14.75 kJ·mol-1 for cis-norpinic acid to 30.35 kJ·mol-1 for cis-pinonic acid. The solubility in water was determined with the dynamic method (solid-liquid phase equilibria method), and then experimental results were interpreted and correlated using three different mathematical models: Wilson, non-random two-liquid model, and universal quasichemical equations. The results of the correlation indicate that the Wilson equation appears to work the best for all investigated compounds, giving rise to the lowest value of a standard deviation. cis-Norpinic acid and cis-pinic acid (dicarboxylic acids) show better solubility in the aqueous solution than cis-norpinonic acid and cis-pinonic acid (monocarboxylic acids), which affect the multiphase chemistry of α-pinene SOA processes. For cis-pinonic acid and cis-norpinonic acid, also pH-profile solubility was determined. The intrinsic solubility (S0) for cis-norpinonic acid was measured to be 0.05 mmol·dm-3, while for cis-pinonic acid, it was found to be 0.043 mmol·dm-3. The acidity constants (pKa) at 298 and 310 K using the Bates-Schwarzenbach spectrophotometric method were determined. The pKa values at 298.15 K for cis-norpinonic acid and cis-pinonic acid were found to be 4.56 and 5.19, respectively, whereas at 310.15 K, pKa values were found to be -4.76 and 5.25, respectively.

Characterization of crucial fragments during the nucleation and growth of secondary organic aerosol from the high-NO photo-oxidation of α-pinene

We propose the use of thermal-desorption dichloromethane-induced low-pressure photoionization mass spectrometry (TD-CH2Cl2-induced LPPI-MS) via a laboratory-built krypton vacuum ultraviolet lamp for the real-time analysis of α-pinene secondary organic aerosol (αP-SOA). Using this technology, the peak intensities of the majority of SOA were enhanced by at least two orders of magnitude after doping with 720 ppm dichloromethane. Clear temporal evolutions of the SOA oxidation products with particle formation were also observed. The molecular ion peaks at m/z value of 153 and 109 showed a similar sharp increase with particle-number concentration. These two species (i.e. protonated α-campholenic aldehyde or dehydrated protonated pinalic-3-acid) with the fragment at m/z 153 and 109 may be critical species to prompt new particle formation. Furthermore, the monomers with the fragment ion peaks at m/z value of 69 and 87 (i.e. protonated pinonic acid, pinic acid, oxopinonic acid, and OH-pinonic acid etc.) were found to be intermediate species with high reactivities during SOA growth. The obtained results provide supplementary knowledge regarding the characterization and temporal evolution of the key components that promote αP-SOA formation.

Online gas- and particle-phase measurements of organosulfates, organosulfonates and nitrooxy organosulfates in Beijing utilizing a FIGAERO ToF-CIMS

Abstract. A time-of-flight chemical ionization mass spectrometer (CIMS) utilizing the Filter Inlet for Gas and Aerosol (FIGAERO) was deployed at a regional site 40 km north-west of Beijing and successfully identified and measured 17 sulfur-containing organics (SCOs are organo/nitrooxy organosulfates and sulfonates) with biogenic and anthropogenic precursors. The SCOs were quantified using laboratory-synthesized standards of lactic acid sulfate and nitrophenol organosulfate (NP OS). The variation in field observations was confirmed by comparison to offline measurement techniques (orbitrap and high-performance liquid chromatography, HPLC) using daily averages. The mean total (of the 17 identified by CIMS) SCO particle mass concentration was 210 ± 110 ng m−3 and had a maximum of 540 ng m−3, although it contributed to only 2 ± 1 % of the organic aerosol (OA). The CIMS identified a persistent gas-phase presence of SCOs in the ambient air, which was further supported by separate vapour-pressure measurements of NP OS by a Knudsen Effusion Mass Spectrometer (KEMS). An increase in relative humidity (RH) promoted partitioning of SCO to the particle phase, whereas higher temperatures favoured higher gas-phase concentrations. Biogenic emissions contributed to only 19 % of total SCOs measured in this study. Here, C10H16NSO7, a monoterpene-derived SCO, represented the highest fraction (10 %) followed by an isoprene-derived SCO. The anthropogenic SCOs with polycyclic aromatic hydrocarbon (PAH) and aromatic precursors dominated the SCO mass loading (51 %) with C11H11SO7, derived from methyl naphthalene oxidation, contributing to 40 ng m−3 and 0.3 % of the OA mass. Anthropogenic-related SCOs correlated well with benzene, although their abundance depended highly on the photochemical age of the air mass, tracked using the ratio between pinonic acid and its oxidation product, acting as a qualitative photochemical clock. In addition to typical anthropogenic and biogenic precursors the biomass-burning precursor nitrophenol (NP) provided a significant level of NP OS. It must be noted that the contribution analysis here is only representative of the detected SCOs. There are likely to be many more SCOs present which the CIMS has not identified. Gas- and particle-phase measurements of glycolic acid suggest that partitioning towards the particle phase promotes glycolic acid sulfate production, contrary to the current formation mechanism suggested in the literature. Furthermore, the HSO4⋅H2SO4- cluster measured by the CIMS was utilized as a qualitative marker for acidity and indicates that the production of total SCOs is efficient in highly acidic aerosols with high SO42- and organic content. This dependency becomes more complex when observing individual SCOs due to variability of specific VOC precursors.

Probing the OH Oxidation of Pinonic Acid at the Air-Water Interface Using Field-Induced Droplet Ionization Mass Spectrometry (FIDI-MS).

Gas and aqueous phases are essential media for atmospheric chemistry and aerosol formation. Numerous studies have focused on aqueous-phase reactions as well as coupled gas/aqueous-phase mass transport and reaction. Few studies have directly addressed processes occurring at the air-water interface, especially involving surface-active compounds. We report here the application of field-induced droplet ionization mass spectrometry (FIDI-MS) to chemical reactions occurring at the atmospheric air-water interface. We determine the air-water interfacial OH radical reaction rate constants for sodium dodecyl sulfate (SDS), a common surfactant, and pinonic acid (PA), a surface-active species and proxy for biogenic atmospheric oxidation products, as 2.87 × 10-8 and 9.38 × 10-8 cm2 molec-1 s-1, respectively. In support of the experimental data, a comprehensive gas-surface-aqueous multiphase transport and reaction model of general applicability to atmospheric interfacial processes is developed. Through application of the model, PA is shown to be oxidized exclusively at the air-water interface of droplets with a diameter of 5 μm under typical ambient OH levels. In the absence of interfacial reaction, aqueous- rather than gas-phase oxidation is the major PA sink. We demonstrate the critical importance of air-water interfacial chemistry in determining the fate of surface-active species.