Cis-pinonic Acid Research Articles

Fragmentation vs. functionalization: chemical aging and organic aerosol formation

Abstract. The transformation process that a carbon backbone undergoes in the atmosphere is complex and dynamic. Understanding all these changes for all the species in detail is impractical; however, choosing different molecules that resemble progressively higher stages of oxidation or aging and studying them can give us an insight into general characteristics and mechanisms. Here we determine secondary organic aerosol (SOA) mass yields of two sequences of molecules reacting with the OH radical at high NOx. Each sequence consists of species with similar vapor pressures, but a succession of oxidation states. The first sequence consists of n-pentadecane, n-tridecanal, 2-, 7-tridecanone, and pinonaldehyde. The second sequence consists of n-nonadecane, n-heptadecanal and cis-pinonic acid. Oxidized molecules tend to have lower relative SOA mass yields; however, oxidation state alone was not enough to predict how efficiently a molecule forms SOA. Certain functionalities are able to fragment more easily than others, and even the position of these functionalities on a molecule can have an effect. n-Alkanes tend to have the highest yields, and n-aldehydes the lowest. n-Ketones have slightly higher yields when the ketone moiety is located on the side of the molecule and not in the center. In general, oxidation products remain efficient SOA sources, though fragmentation makes them less effective than comparable alkanes.

Seasonal variation in the biogenic secondary organic aerosol tracer cis-pinonic acid: Enhancement due to emissions from regional and local biomass burning

Studies have demonstrated that cis-pinonic acid (CPA) is an important product from the oxidation of pinenes with ozone. CPA has been measured on aerosols and is used as an aging indicator for secondary organic aerosols (SOA). CPA levels and formation in urban aerosols and its annual variability, however, are still poorly understood. Here, we present monthly CPA average concentrations on aerosols in Toronto, Ontario, Canada based on a two-year-period: 2000–2001. They displayed a seasonal pattern associated with temperature and ozone (O3) plus nitrogen dioxide (NO2) reflecting the influence these have on emissions of pinenes from forests and their atmospheric oxidation, respectively. However, in Toronto some months with higher CPA concentrations, especially in the winter, were inconsistent with the seasonality of temperature or/and O3 + NO2 levels. Instead these deviations were associated with increases in wood burning tracers such as dehydroabietic acid (DHAA) and sugars. Similar features were observed during a two-week-period comparing day and nighttime CPA concentrations in the Lower Fraser Valley (LFV) of British Columbia, Canada, in that the CPA concentrations clearly varied diurnally with temperature and O3 + NO2 on some days, but also showed a significant correspondence with variations in the wood burning tracer concentrations, such as levoglucosan. These findings demonstrate that CPA formation is strongly impacted by wood burning activity.

Ionic liquid-functionalized silica for selective solid-phase extraction of organic acids, amines and aldehydes

Three ionic liquid (IL)-functionalized silica materials, imidazolium, N-methylimidazolium and 1-alkyl-3-(propyl-3-sulfonate) imidazolium, were synthesised and applied in solid-phase extraction (SPE) of organic acids, amines and aldehydes, which are important compound families in atmospheric aerosol particles. 1-Alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica was tested as sorbent for SPE for the first time. The analytes were separated and detected by liquid chromatography–mass spectrometry (LC–MS). To confirm the results achieved by LC–MS, the acids were additionally determined by gas chromatography–mass spectrometry (GC–MS). The stability of the IL-functionalized silica materials was tested at low and high pH. The effect of the pH on the extraction was also informative of the retention mechanism of the materials. The results showed anion exchange to be the main interaction, but hydrophobic and π interactions and hydrogen bonding also played a role in the extraction. Extraction efficiencies for organic acids ranged from 87 to 110%, except for cis-pinonic acid (19–29%). Lower extraction efficiencies for amines and aldehydes confirmed that anionic exchange was the predominant interaction. Comparisons made with two commercial SPE materials—silica-based strong anion exchange (SAX) and polymer-based mixed-mode anion exchange and reverse-phase (MAX)—showed the IL-functionalized materials to offer different selectivity and better extraction efficiency than SAX for aromatic compounds. Finally, the new materials were successfully tested in the extraction of an atmospheric aerosol sample.

Model HULIS compounds in nanoaerosol clusters – investigations of surface tension and aggregate formation using molecular dynamics simulations

Abstract. Cloud condensation nuclei act as cores for water vapour condensation, and their composition and chemical properties may enhance or depress the ability for droplet growth. In this study we use molecular dynamics simulations to show that model humic-like substances (HULIS) in systems containing 10 000 water molecules mimic experimental data well referring to reduction of surface tension. The model HULIS compounds investigated in this study are cis-pinonic acid (CPA), pinic acid (PAD) and pinonaldehyde (PAL). The structural properties examined show the ability for the model HULIS compounds to aggregate inside the nanoaerosol clusters.

Characterization of carboxylic acids in atmospheric aerosols using hydrophilic interaction liquid chromatography tandem mass spectrometry

A sensitive hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry (HILIC/ESI-MS/MS) method was developed for determination of selected aliphatic (i.e. malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, maleic, fumaric, glycolic and pyruvic acid), alicyclic (i.e. cis-pinonic and pinic acid) and aromatic (i.e. trimesic, phthalic acid and its isomers) carboxylic acids. Analytes were separated on an amide column using a gradient elution with a 10 mM constant ionic strength mobile phase containing acetonitrile and aqueous ammonium acetate buffer (pH 5.0). The influence of the buffer type, pH, polar modifier and temperature on analyte retention under HILIC was studied. Static sonication-assisted solvent extraction was optimized for sample preparation prior to analysis. The recoveries obtained were higher than 90% for most analytes. The method was proven to be sensitive with limits of detection ranged from 0.03 to 16.0 μg/L in selected reaction monitoring mode (SRM). The repeatability and intermediate precision of the method, expressed as RSD (%) of the peak area ratio between analytes and their internal standards were generally lower than 5%. The method was successfully applied for determination of the studied acids in samples of ambient aerosol particles. A big advantage of the new method is also its ability to detect and separate the isobaric compounds of the selected carboxylic acids. Our results demonstrate that the method is specific and sensitive for the determination of a wider range of polar carboxylic acids at low concentrations in complex samples of aerosol particles.

Joint effect of organic acids and inorganic salts on cloud droplet activation

Abstract. We have investigated CCN properties of internally mixed particles composed of one organic acid (oxalic acid dihydrate, succinic acid, adipic acid, citric acid, cis-pinonic acid, or Nordic reference fulvic acid) and one inorganic salt (sodium chloride or ammonium sulphate). Surface tension and water activity of aqueous model solutions with concentrations relevant for CCN activation were measured using a tensiometer and osmometry, respectively. The measurements were used to calculate Köhler curves and critical supersaturations, which were compared to measured critical supersaturations of particles with the same chemical compositions, determined with a cloud condensation nucleus counter. Surfactant surface partitioning was not accounted for. For the aqueous solutions containing cis-pinonic acid and fulvic acid, a depression of surface tension was observed, but for the remaining solutions the effect on surface tension was negligible at concentrations relevant for cloud droplet activation. The surface tension depression of aqueous solutions containing both organic acid and inorganic salt was approximately the same as or smaller than that of aqueous solutions containing the same mass of the corresponding pure organic acids. Water activity was found to be highly dependent on the type and amount of inorganic salt. Sodium chloride was able to decrease water activity more than ammonium sulphate and both inorganic salts are predicted to have a smaller Raoult term than the studied organic acids. Increasing the mass ratio of the inorganic salt led to a decrease in water activity. Water activity measurements were compared to results from the E-AIM model and values estimated from both constant and variable van't Hoff factors. The correspondence between measurements and estimates was overall good, except for highly concentrated solutions. Critical supersaturations calculated with Köhler theory based on measured water activity and surface tension, but not accounting for surface partitioning, compared well with measurements, except for the solutions containing sodium chloride and oxalic acid or one of the more surface active organic compounds. In such cases, significantly lower values were obtained from Köhler theory than the measured critical supersaturations with deviations above 50% for a 60 nm particle containing 50% (dry mass) of Nordic reference fulvic acid, suggesting that surfactant partitioning and/or an effect of sodium chloride on solubility of the organic component is important.

Mass spectrometric characterization of isomeric terpenoic acids from the oxidation of α‐pinene, β‐pinene, d‐limonene, and Δ3‐carene in fine forest aerosol

In this study, we present liquid chromatographic and mass spectral data for predominant terpenoic acids formed through oxidation of α-pinene, β-pinene, d-limonene, and Δ(3)-carene that occur in fine forest aerosol from K-puszta, Hungary, a rural site with coniferous vegetation. Characterization of these secondary organic aerosol tracers in fine ambient aerosol is important because it allows one to gain information on monoterpene precursors and source processes such as oxidation and aging processes. The mass spectral data were obtained using electrospray ionization in the negative ion mode, accurate mass measurements, and linear ion trap tandem mass spectrometric experiments. Emphasis is given to the mass spectrometric differentiation of isobaric terpenoic acids, such as, e.g. the molecular weight (MW) 186 terpenoic acids, cis-pinic, cis-caric, homoterpenylic, ketolimononic, and limonic acids. Other targeted isobaric terpenoic acids are the MW 184 terpenoic acids, cis-pinonic and cis-caronic acids, and the MW 204 tricarboxylic acids, 3-methyl-1,2,3-butanetricarboxylic and 3-carboxyheptanedioic acids. Fragmentation pathways are proposed to provide a rational explanation for the observed isomeric differences and/or to support the suggested tentative structures. For the completeness of the data set, data obtained for recently reported lactone-containing terpenoic acids (i.e. terpenylic and terebic acids), related or isobaric compounds (i.e. norpinic acid, diaterpenylic acid acetate, and unknown MW 188 compounds) are also included, the rationale being that other groups working on this topic could use this data compilation as a reference.

2-azapinanes: aza analogues of the enantiomeric pinyl carbocation intermediates in pinene biosynthesis.

The enantiomeric 2-azapinanes, aza analogues of the pinyl carbocation intermediates in pinene biosynthesis, were synthesized from (-)- and (+)-cis-pinonic acids. The individual reactions in the 5-step sequence were Beckmann rearrangement of the pinonic acid oximes, cyclization to the N-acetyl lactams, hydrolysis to the NH-lactams, N-methylations, and LiAlH(4) reductions. The anti stereochemistry of the N-methyl groups in the salts with respect to the gem-dimethyl bridge was established by NOE measurements and by X-ray diffraction analysis.

Solid state and sub-cooled liquid vapour pressures of cyclic aliphatic dicarboxylic acids

Abstract. Knudsen Effusion Mass Spectrometry (KEMS) has been used to measure for the first time the solid state vapour pressures of a series of aliphatic cyclic dicarboxylic acids with increasing ring size. Additionally the atmospherically important compounds; cis-pinonic acid and levoglucosan were also measured. Differential Scanning Calorimetry (DSC) was used to measure melting points, enthalpies and entropies of fusion, which were used to determine sub-cooled liquid vapour pressures for the compounds. The sub-cooled liquid vapour pressure of straight chain, branched and cyclic dicarboxylic acids was compared to a selection of estimation methods.

The influence of temperature and aerosol acidity on biogenic secondary organic aerosol tracers: Observations at a rural site in the central Pearl River Delta region, South China

At a rural site in the central Pearl River Delta (PRD) region in south China, fine particle (PM2.5) samples were collected during fall-winter 2007 to measure biogenic secondary organic aerosol (SOA) tracers, including isoprene SOA tracers (3-methyl-2,3,4-trihydroxy-1-butene, 2-methylglyceric acid, 2-methylthreitol and 2-methylerythritol), α-pinene SOA tracers (cis-pinonic acid, pinic acid, 3-methyl-1,2,3-butanetricarboxylic acid, 3-hydroxyglutaric acid and 3-hydroxy-4,4-dimethylglutaric acid) and a sesquiterpene SOA tracer (β-caryophyllinic acid). The isoprene-, α-pinene- and sesquiterpene-SOA tracers averaged 30.8 ± 15.9, 6.61 ± 4.39, and 0.54 ± 0.56 ng m−3, respectively; and 2-methyltetrols (sum of 2-methylthreitol and 2-methylerythritol, 27.6 ± 15.1 ng m−3) and cis-pinonic acid (3.60 ± 3.76 ng m−3) were the dominant isoprene- and α-pinene-SOA tracers, respectively. 2-Methyltetrols exhibited significantly positive correlations (p < 0.05) with ambient temperature, probably resulting from the enhanced isoprene emission strength and tracer formation rate under higher temperature. The significantly positive correlation (p < 0.05) between 2-methyltetrols and the estimated aerosol acidity with a slope of 59.4 ± 13.4 ng m−3 per μmol [H+] m−3 reflected the enhancement of isoprene SOA formation by aerosol acidity, and acid-catalyzed heterogeneous reaction was probably the major formation pathway for 2-methyltetrols in the PRD region. 2-Methylglyceric acid showed poor correlations with both temperature and aerosol acidity. The α-pinene SOA tracers showed poor correlations with temperature, probably due to the counteraction between temperature effects on the precursor emission/tracer formation and gas/particle partitioning. Among the α-pinene SOA tracers, only cis-pinonic acid and pinic acid exhibited significant correlations with aerosol acidity with slopes of −11.7 ± 3.7 and −2.2 ± 0.8 ng m−3 per μmol [H+] m−3, respectively. The negative correlations observed for α-pinene SOA tracers might result from their transfer from particle to gas phase with the increase of aerosol acidity. The ratio of cis-pinonic acid plus pinic acid to 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) ranged from 0.28 to 28.9 with a mean of 7.19, indicating the relatively fresh α-pinene SOA tracers during our campaign.

Composition of semi-volatile organic compounds in the urban atmosphere of Singapore: influence of biomass burning

Abstract. An intensive field study was conducted in the urban atmosphere of Singapore to investigate the composition of organic compounds in both gaseous and particulate phases during the period of August to early November 2006. 17 atmospheric samples were collected. These samples were subjected to accelerated solvent extraction with a mixture of dichloromethane and acetone and separated into functional group fractions for analyses by GC/MS. Over 180 organic compounds belonging to three major fractions (n-alkanes, polycyclic aromatic hydrocarbons – PAHs, and polar organic compounds – POCs) were identified and quantified. The characteristics and abundance of the n-alkanes, PAHs, mono and dicarboxylic acids, methoxylated phenols and other POCs were determined. The composition of these organic compounds fluctuated temporally with most of them being relatively higher in October than those in other months of the sampling period. 3-D backward air mass trajectory analyses together with the carbon preference index (CPI), molecular diagnostic ratios and molecular markers were used to investigate the origin of organic species measured in this study. Based on these diagnostic tools, the increased abundance of atmospheric organic species during October could be attributed to the occurrence of regional smoke haze episodes due to biomass burning in Indonesia. Among the POCs investigated, phthalic acid and cis-pinonic acid were abundant during October 2006. These two acids showed strong linear relationships with maximum daily ozone concentrations throughout the entire sampling period. This correlation with ozone suggested that the secondary aerosol constituents such as phthalic and cis-pinonic acids were probably formed through O3-induced photochemical transformation.

Development and characterization of a High-Temperature Proton-Transfer-Reaction Mass Spectrometer (HT-PTR-MS)

Abstract. We have developed a High-Temperature Proton-Transfer-Reaction Mass Spectrometer (HT-PTR-MS) in which both the ion source and the ion drift tube can be continuously operated at temperatures up to 250 °C. The instrument was characterized in a high E/N-mode (130 Td) and in a low E/N-mode (87 Td) at an operating temperature of 200 °C. Instrumental sensitivities and 2σ-detection limits were on the order of 50–110 cps/ppb and 100 ppt (1 s signal integration time), respectively. The HT-PTR-MS is primarily intended for measuring "sticky" or semi-volatile trace gases. Alternatively, it may be coupled to a particle collection/thermal desorption apparatus to measure particle-bound organics in near real-time. In view of these applications, we have measured instrumental response times for a series of reference compounds. 1/e2-response times for dimethyl sulfoxide, ammonia and monoethanolamine were in the sub-second to second regime. 1/e2-response times for levoglucosan, oxalic acid and cis-pinonic acid ranged from 8 to 370 s.

Surface-Active cis-Pinonic Acid in Atmospheric Droplets: A Molecular Dynamics Study

Water vapor in the atmosphere can condensate and form cloud droplets when there is a certain amount of humidity and a presence of cloud condensation nuclei, and organic solutes called surfactants can significantly lower the surface tension of water — one of the parameters determining cloud droplet population. We here present a molecular dynamics study of the behavior of cis-pinonic acid, a commonly found organic compound in cloud condensation nuclei, and its effect on the surface tension of water clusters. Specifically, the decrease in surface tension is found to depend on not only the concentration of the organic compound but also the droplet size due to the spontaneous assembly of the surfactant molecules on the droplet surface. This leads to the conclusion that the partitioning of the surfactant between the bulk and surface plays an important role in the behavior of atmospheric aerosol particles and thus in their availability for cloud formation.

Solid-phase extraction of organic compounds in atmospheric aerosol particles collected with the particle-into-liquid sampler and analysis by liquid chromatography–mass spectrometry

Atmospheric aerosol particles, collected with the particle-into-liquid sampler at SMEARII station in Finland in mid-August 2007, were analysed for biogenic acids. The sample pretreatment method, comprising solid-phase extraction with anion exchange and hydrophilic–lipophilic balance materials, was optimized. Extraction efficiencies of solid-phase extraction from 10 and 20 ml samples were about 100%, with average relative standard deviation of 8.9%, in concentration range from 12.5 to 50 ng/ml of the acid. Extraction of aldehydes was less successful, with efficiencies from 69 to 163% and average 10% deviation. Pretreated samples were analysed by reversed phase high performance liquid chromatography with ion trap mass spectrometric detection. Limits of detection achieved for organic acids with the analytical procedure developed ranged from 9 to 27 μg/l of extracted sample, while limits of quantitation were from 31 to 90 μg/l. Oxidation with ozone was used for the preparation of the acid of β-caryophyllene (β-caryophyllinic acid), which was also studied in aerosol samples. MS 2 experiments were used to confirm the identification of trans-pinic, trans-pinonic and β-caryophyllinic acids. Azelaic, hexadecanoic, cis-pinonic, and cis- and trans-pinic acids were quantitated in the samples with use of authentic standards, while the concentrations of trans-pinonic and β-caryophyllinic acids were determined with cis-pinonic acid as surrogate. Also, the contribution of β-caryophyllene oxidation products to aerosol organic carbon was evaluated. Aldehydes could not be analysed in real samples due to the insufficient extraction. The particle-into-liquid sampler proved to be suitable for the collection of aerosol particles for the elucidation of daily and diurnal variation of selected species. The optimized sample pretreatment, together with the analysis method, offer a promising approach for the study of aerosol chemical composition, where artifact formation is minimal and time resolution is good.

Roadside, Urban, and Rural Comparison of Primary and Secondary Organic Molecular Markers in Ambient PM2.5

PM2.5 filter samples (12-h and 24-h) were collected in urban Atlanta, GA, next to a freeway and 400 m away, as well as at a rural site, with particular focus on exploring on-road emissions, regional transport, and biogenic effects. Detailed speciation of PM2.5 carbonaceous aerosols was conducted by GC/ MS. Diurnal, seasonal, and spatial variations of PM2.5 organic composition were investigated. Primary organic compounds usually exhibit different attributes of day vs night while secondary organic tracers varied little. Much higher concentrations of automotive-related primary organic compounds are observed at the highway site, including n-alkanes, hopanes, steranes, and polycyclic aromatic hydrocarbons (PAHs). Season-specific on-road mobile source primary OC profiles were developed by using differences in organic species concentrations between the highway site and the nearby site. Calculated on-road source profiles differ from mobile source profiles measured in the lab. Significant seasonal differences are observed for 2-methyltetrols, cis-pinonic acid, and pinic acid, organic tracers of biogenic secondary organic aerosols (SOA). Little correlation is found between 2-methyltetrols and cis-pinonic or pinic acid, though cis-pinonic and pinic acids are strongly correlated.

Hydrogen-Bonding Interaction in Molecular Complexes and Clusters of Aerosol Nucleation Precursors

Complexes and clusters bridge the gap between molecular and macroscopic levels by linking individual gaseous molecules to newly formed nanoparticles but the driving forces and mechanism for the formation of complexes and clusters in the atmosphere are not well understood. We have performed ab initio and density functional quantum chemical calculations to elucidate the role of organic acids in the formation of complexes with common atmospheric nucleating precursors such as sulfuric acid, water, and ammonia. A central feature of the complexes is the presence of two hydrogen bonds. Organic acid-sulfuric acid complexes show one strong and one medium-strength hydrogen bond whereas the corresponding hydrogen bonds in organic acid-ammonia complexes are characterized as medium-strength and weak. The formation of strong hydrogen bonds in organic acid-sulfuric acid complexes is explained by the well-established resonance-assisted hydrogen bonding theory. Organic acid-sulfuric acid and organic acid-organic acid complexes possess the largest binding energies among the homomolecular and heteromolecular dimers, about 18 kcal mol(-1) from the composite theoretical methods. Topological analysis employing quantum theory of atoms in molecules (QTAIM) shows that the charge density and the Laplacian at bond critical points (BCPs) of the hydrogen bonds of the organic acid-sulfuric acid complex (e.g., benzoic acid-sulfuric acid and cis-pinonic acid-sulfuric acid) are 0.07 and 0.16 au, respectively, which falls in or exceeds the range of one strong and one medium-strength hydrogen bonding criteria.

Spatial and Seasonal Trends in Biogenic Secondary Organic Aerosol Tracers and Water-Soluble Organic Carbon in the Southeastern United States

Twenty-four hour integrated filter samples of fine particulate matter (PM2.5) were collected from May 2004 to April 2005 at one rural site and three urban sites located in the southeastern United States. Filters were extracted and analyzed for both biogenic secondary organic aerosol (SOA) tracers via gas chromatography-mass spectrometry (GC-MS), and water-soluble organic carbon (WSOC) concentrations. The tracers reported in this study include isoprene-derived 2-methylthreitol and 2-methylerythritol, as well as pinene-derived cis-pinonic acid. The mean ambient concentrations ranged from 21.7 to 94.3 ng/m3, 5.31 to 17.9 ng/m3, and 1.87 to 3.18 microgC/m3 for 2-methyltetrols (sum of 2-methylerythritol and 2-methylthreitol), cispinonic acid and WSOC, respectively. Distinct spatial distributions were observed for all tracers with the highest concentration at the rural site and the lowest level at a coastal site. Although 2-methyltetrols were small fractions of WSOC, varying from 0.35% at an urban site to highest fractions of 1.09% at the rural site, WSOC exhibited significant correlation with 2-methyltetrols during summer, suggesting isoprene SOA makes an important contribution to WSOC. 2-Methyltetrols had the highest concentrations during the summer,when high temperature, intense solar radiation, and high ozone level occurred. However, no obvious seasonal variation was found for cispinonic acid. Between inland sites WSOC was more spatially homogeneous than the 2-methyltetrols, suggesting that WSOC was produced from a variety of mechanisms.

Modelling the cloud condensation nucleus activity of organic acids on the basis of surface tension and osmolality measurements

Abstract. In this study vapour pressure osmometry was used to determine water activity in the solutions of organic acids. The surface tension of the solutions was also monitored in parallel and then Köhler curves were calculated for nine organic acids (oxalic, malonic, succinic, glutaric, adipic, maleic, malic, citric and cis-pinonic). Surface tension depression is negligible for most of the organic acids in dilute (≤1 w/w%) solutions. Therefore, these compounds affect equilibrium vapour pressure only in the beginning phase of droplet formation when the droplet solution is more concentrated but not necessarily at the critical size. An exception is cis-pinonic acid which remarkably depress surface tension also in dilute (0.1 w/w%) solution and hence at the critical point. The surface tension of organic acid solutions is influenced by the solubility of the compound, the length of the carbon chain and also by the polar functional groups present in the molecule. Similarly to surface tension solubility plays an important role also in water activity: compounds with higher solubility (e.g. malonic, maleic and glutaric acid) reduce water activity significantly in the early phase of droplet formation while less soluble acids (e.g. succinic and adipic acid) are saturated in small droplets and the solution starts diluting only in bigger droplets. As a consequence, compounds with lower solubility have a minor effect on water activity in the early phase of droplet formation. To deduce the total effect Köhler curves were calculated and critical supersaturations (Sc) were determined for the organic acids using measured surface tension and water activity. It was found that critical supersaturation grew with growing carbon number. Oxalic acid had the lowest critical supersaturation in the size range studied and it was comparable to the activation of ammonium sulphate. The Sc values obtained in this study were compared to data from CCNC experiments. In most cases good agreement was found. For modelling purposes Sc vs. ddry plots are given and the dependence of water activity and surface tension on concentration are also formulated.

Effect of Ammonia on Secondary Organic Aerosol Formation from α-Pinene Ozonolysis in Dry and Humid Conditions

This study examines the influence of ammonia (NH3) on secondary organic aerosol (SOA) formation from the alpha-pinene/ozone oxidation system for dry and humid conditions. Aerosol yield differed depending on which OH scavenger was used, with the highest yield noted for CO, followed by cyclohexane and 2-butanol. Number and volume concentrations were quickly increased within the reactor by 15 and 8%, respectively, when NH3 was added after the reaction ceased. The increase in number concentration indicated the formation of new particles resulting from gas-to-particle conversion. Moreover, average particle size increased from 242 to 248 nm. The resulting aerosol growth was attributed to ammonium salts formed by the reaction between organic acids and NH3. When NH3 was added to aerosolized cis-pinonic acid in the environmental reactor, a dramatic increase in both number and volume concentrations of cis-pinonic acid was observed. This provides further evidence that NH3 can interact with gas-phase organic acids forming condensable salts and thereby enhancing SOA formation. Initially present NH3 significantly enhanced aerosol yield in alpha-pinene-ozone reactions, regardless of the presence of water vapor. The role of NH3 on SOA formation in the dry and humid conditions is discussed in terms of a theoretical modeling study.

Surface tension of aqueous solutions of water-soluble organic and inorganic compounds

Surface tension of pure and mixed aqueous solutions of both inorganic and organic species that are relevant in atmospheric droplets has been studied in a laboratory investigation. Following the Gibbsian theory of surfaces experimental data have been fitted by the Szyszkowski equation. As a function of the carbon-chain length trends in the maximum surface excess Γ max and the inverse surface activity β have been clearly identified for pure aqueous solutions of homologous series of n-alcohols and mono-carboxylic acids, while these parameters oscillate for the homologous series of di-carboxylic acids. For mixed aqueous solutions of water-soluble organic and inorganic compounds, e.g. cis-pinonic acid and sodium chloride, a further decrease in surface tension has been observed, which can be interpreted as an interaction between the inorganic and organic solutes and an enrichment of the surface-active organic compound in the surface layer. Taking this effect into account surface-tension data of real atmospheric samples become more plausible, especially when also slightly soluble or water-insoluble organic compounds having a high surface activity at low concentrations are considered.