Pinic Acid Research Articles

Multifunctional acid formation from the gas-phase ozonolysis of β-pinene

The gas-phase ozonolysis of beta-pinene was studied in static chamber experiments, using gas chromatography coupled to mass spectrometric and flame ionisation detection to separate and detect products. A range of multifunctional organic acids-including pinic acid, norpinic acid, pinalic-3-acid, pinalic-4-acid, norpinalic acid and OH-pinalic acid-were identified in the condensed phase after derivatisation. Formation yields for these products under systematically varying reaction conditions (by adding different OH radical scavengers and Criegee intermediate scavengers) were investigated and compared with those observed from alpha-pinene ozonolysis, allowing detailed information on product formation mechanisms to be elucidated. In addition, branching ratios for the initial steps of the reaction were inferred from quantitative measurements of primary carbonyl formation. Atmospheric implications of this work are discussed.

Cloud Activating Properties of Aerosol Observed during CELTIC

Abstract Measurements of aerosol size distribution, chemical composition, and cloud condensation nuclei (CCN) concentration were performed during the Chemical Emission, Loss, Transformation, and Interactions with Canopies (CELTIC) field program at Duke Forest in North Carolina. A kinetic model of the cloud activation of ambient aerosol in the chamber of the CCN instrument was used to perform an aerosol–CCN closure study. This study advances prior investigations by employing a novel fitting algorithm that was used to integrate scanning mobility particle sizer (SMPS) measurements of aerosol number size distribution and aerosol mass spectrometer (AMS) measurements of the mass size distribution for sulfate, nitrate, ammonium, and organics into a single, coherent description of the ambient aerosol in the size range critical to aerosol activation (around 100-nm diameter). Three lognormal aerosol size modes, each with a unique internally mixed composition, were used as input into the kinetic model. For the two smaller size modes, which control CCN number concentration, organic aerosol mass fractions for the defined cases were between 58% and 77%. This study is also unique in that the water vapor accommodation coefficient was estimated based on comparing the initial timing for CCN activation in the instrument chamber with the activation predicted by the kinetic model. The kinetic model overestimated measured CCN concentrations, especially under polluted conditions. Prior studies have attributed a positive model bias to an incomplete understanding of the aerosol composition, especially the role of organics in the activation process. This study shows that including measured organic mass fractions with an assumed organic aerosol speciation profile (pinic acid, fulvic acid, and levoglucosan) and an assumed organic aerosol solubility of 0.02 kg kg−1 still resulted in a significant model positive bias for polluted case study periods. The slope and y intercept for the CCN predicted versus CCN observed regression was found to be 1.9 and −180 cm−3, respectively. The overprediction generally does not exceed uncertainty limits but is indicative that a bias exists in the measurements or application of model. From this study, uncertainties in the particle number and mass size distributions as the cause for the model bias can be ruled out. The authors are also confident that the model is including the effects of growth kinetics on predicted activated number. However, one cannot rule out uncertainties associated with poorly characterized CCN measurement biases, uncertainties in assumed organic solubility, and uncertainties in aerosol mixing state. Sensitivity simulations suggest that assuming either an insoluble organic fraction or external aerosol mixing were both sufficient to reconcile the model bias.

Primary source attribution and analysis of α-pinene photooxidation products in Duke Forest, North Carolina

Samples of fine particulate organic matter were collected outside Durham, NC in the Duke Research Forest as part of the CELTIC study in July 2003. Particulate samples were collected on quartz filters using high volume air sampling equipment, and samples were analyzed for polar and non-polar organic species. Among compounds analyzed, oxidation products of α-pinene, namely pinic acid and pinonic acid, were identified in all samples. Pinic acid, being a dicarboxylic acid, has a low vapor pressure of the order of 10 −8 Torr and is expected to contribute significantly to secondary organic aerosol (SOA) formation from the oxidation of α-pinene. Source contribution estimates from primary organic aerosol emissions were computed using the organic species as molecular markers with the chemical mass balance (CMB) model. The unapportioned organic carbon (OC) was determined as the difference between measured OC and OC apportioned to primary sources. This unapportioned OC was then correlated with pinic and pinonic acid to get a better understanding of the role of monoterpene oxidation products to form SOA. A reasonably good fit between pinic acid concentrations and unapportioned OC levels is indicative of the contribution of α-pinene oxidation products to SOA formation in ambient atmosphere. The results are significant considering the role of monoterpene emissions to global atmospheric chemistry.

Hydroxydicarboxylic Acids: Markers for Secondary Organic Aerosol from the Photooxidation of α-Pinene

Detailed organic analysis of fine (PM2.5) rural aerosol collected during summer at K-puszta, Hungary from a mixed deciduous/coniferous forest site shows the presence of polar oxygenated compounds that are also formed in laboratory irradiated alpha-pinene/NOx/air mixtures. In the present work, two major photooxidation products of alpha-pinene were characterized as the hydroxydicarboxylic acids, 3-hydroxyglutaric acid, and 2-hydroxy-4-isopropyladipic acid, based on chemical, chromatographic, and mass spectral data. Different types of volatile derivatives, including trimethylsilyl ester/ether, methyl ester trimethylsilyl ether, and ethyl ester trimethylsilyl ether derivatives were measured by gas chromatography/mass spectrometry (GC/MS), and their electron ionization (El) spectra were interpreted in detail. The proposed structures of the hydroxydicarboxylic acids were confirmed or supported with reference compounds. 2-Hydroxy-4-isopropyladipic acid formally corresponds to a further reaction product of pinic acid involving addition of a molecule of water and opening of the dimethylcyclobutane ring; this proposal is supported by a laboratory irradiation experiment with alpha-pinene/NOJ0 air. In addition, we report the presence of a structurally related minor alpha-pinene photooxidation product, which was tentatively identified as the C7 homolog of 3-hydroxyglutaric acid, 3-hydroxy-4,4-dimethylglutaric acid. The detection of 2-hydroxy-4-isopropyladipic acid in ambient aerosol provides an explanation for the relatively low atmospheric concentrations of pinic acid found during daytime in forest environments.

Pinic and pinonic acid formation in the reaction of ozone with α-pinene

The mechanism of formation of key compounds in atmospheric secondary aerosol (SOA) has been investigated by studying the products of the ozonolysis of an enal derived from alpha-pinene using gas chromatography coupled to mass spectrometry.

Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 3: Carboxylic and dicarboxylic acids

The term “accretion reactions” has been used to describe the collection of reactions by which organic compounds can react with one another and/or other atmospheric constituents, forming products of higher-molecular weight (MW) and lower volatility, and thus increasing their tendency to condense [Barsanti, K.B., Pankow, J.F., 2004. Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 1: Aldehydes and ketones. Atmospheric Environment 38, 4371–4382; Barsanti, K.B., Pankow, J.F., 2005. Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 2: Dialdehydes, methylglyoxal, and diketones. Atmospheric Environment 39, 6597–6607]. Studies have shown that a significant fraction of atmospheric organic particulate matter (OPM) may be comprised of high-MW/low-volatility compounds [e.g., Havers, N., Burpa, P., Lambert, J., Klockow, D., 1998. Spectroscopic characterization of humic-like substances in airborne particulate matter. Journal of Atmospheric Chemistry 29, 45–54], which would be consistent with the occurrence of such accretion reactions in the atmosphere, [e.g., Jang, M., Czoschke, N. M., Lee, S., Kamens, R. M., 2002. Heterogeneous atmospheric organic aerosol production by acid-catalyzed particle-phase reactions. Science 298, 814–817]. However, many uncertainties exist regarding accretion reactions as they may occur in the atmosphere, including identification of those reactions most likely to contribute to OPM. Barsanti and Pankow (2004, 2005) have developed and applied a general theoretical approach to evaluate the thermodynamic favorabilities of accretion reactions, including the extents to which they may be relevant for OPM formation in the atmosphere. That approach is applied here in the consideration of OPM formation by reactions of four mono- and dicarboxylic acids (acetic, malic, maleic, and pinic) to form esters and amides. It was concluded that for all of the acids considered, ester and amide formation are thermodynamically favored under the assumed conditions. For malic, maleic, and pinic acids, and likely for similar mono- and dicarboxylic acids, significant OPM formation may occur via ester and amide formation in the atmosphere when kinetically favorable.

Secondary organic aerosols formed from oxidation of biogenic volatile organic compounds in the Sierra Nevada Mountains of California

Biogenic volatile organic compound (BVOC) emissions, such as isoprene and terpenes, can be oxidized to form less volatile carbonyls, acids, and multifunctional oxygenated products that may condense to form secondary organic aerosols (SOA). This research was designed to assess the contribution of oxidized BVOC emissions to SOA in coniferous forests by collecting high‐volume particulate samples for 6 days and 5 nights in the summer of 2003. The samples were analyzed for acids, carbonyls, polyols and alkanes to quantify oxidized BVOCs. Terpene and isoprene oxidation products were among the most abundant chemical species detected with the exception of hexadecanoic acid, octadecanoic acid and two butyl esters of unknown origin. The terpene oxidation products of pinonic acid, pinic acid, nopinone and pinonaldehyde showed clear diurnal cycles with concentrations two‐ to eight‐fold higher at night. These cycles resulted from the diurnal cycles in gaseous terpene concentrations and lower temperatures that enhanced condensation of semivolatile chemicals onto aerosols. The terpene‐derived compounds averaged 157 ± 118 ng/m3 of particulate organic matter while the isoprene oxidation compounds, namely the 2‐methyltetrols and 2‐methylglyceric acid, accounted for 53 ± 19 ng/m3. Together, the terpene and isoprene oxidation products represented 36.9% of the identified organic mass of 490 ± 95 ng/m3. PM10 organic matter loadings in the region were approximately 2.1 ± 1.2 μg/m3, so about 23% of the organic matter was identified and at least 8.6% was oxidized BVOCs. The BVOC oxidation products we measured were significant, but not dominant, contributors to the regional SOA only 75 km downwind of the Sacramento urban area.

Particle Size Distributions of Organic Aerosol Constituents during the 2002 Yosemite Aerosol Characterization Study

The Yosemite Aerosol Characterization Study (YACS) was conducted in the summer of 2002 to investigate sources of regional haze in Yosemite National Park. Organic carbon and molecular source marker species size distributions were investigated during hazy and clear periods. More than 75% of the organic carbon mass was associated with submicron aerosol particles. Most molecular marker species for wood smoke, an important source of particulate matter during the study, were contained in submicron particles, although on some fire influenced days, levoglucosan shifted toward larger sizes. Various wood smoke marker species exhibited slightly different size distributions in the samples, suggesting different, size dependent emission or atmospheric processing rates of these species. Secondary biogenic compounds including pinic and pinonic acids were associated with smaller particles. Pinonaldehyde, however, exhibited a broader distribution, likely due to its higher volatility. Dicarboxylic acids were associated mainly with submicron particles. Hopanes, molecular markers for vehicle emissions, were mostly contained in smaller particles but exhibited some tailing into larger size classes.

A group contribution method for estimating the vapour pressures of α-pinene oxidation products

Abstract. A prediction method based on group contribution principles is proposed for estimating the vapour pressure of α-pinene oxidation products. Temperature dependent contributions are provided for the following chemical groups: carbonyl, nitrate, hydroxy, hydroperoxy, acyl peroxy nitrate and carboxy. On the basis of observed vapour pressure differences between isomers of diols and dinitrates, a simple refinement is introduced in the method to account for the influence of substitutions on the vapour pressure for alcohols and nitrates. The vapour pressures predicted with this new method have been compared with the predictions from UNIFAC (Asher et al., 2002). Given the large uncertainties of the vapour pressure data for the least volatile compounds, further experimental studies of subcooled vapour pressures of multifunctional compounds at ambient temperatures are required for better parameterizations. Among the α-pinene products identified to date, pinic acid and hydroxy pinonic acid are predicted to be the least volatile compounds, with estimated vapour pressures of 3×10−6 torr and 6×10−7 torr, respectively. The vapour pressure of the other primary products range from 10−5 to 10−3 torr, with hydroxy hydroperoxides presenting the lowest values. Noting that multifunctional carboxylic acids, in particular pinic acid, are believed to be mostly present as dimers in laboratory conditions, we suggest that the partial vapour pressure of the pinic acid dimer should be close to the experimental subcooled vapour pressure for pinic acid (estimated at ~10−6 torr) due to its large contribution to the total concentration (dimer+monomer) in experimental conditions.

Biogenic contributions to the chemical composition of airborne particles in a coniferous forest in Germany

Airborne particles in and above the canopy of a middle European spruce forest were investigated in summer 2001 and in day/night rhythm in summer 2002 near Waldstein site (Fichtelgebirge, Germany). The particles were size-segregated collected and analyzed for main components (inorganic ions, elemental and organic carbon) as well as oxalic acid and alkanes. A mass closure for the chemical composition including water was performed successfully for both years. For analysis of other organic compounds high volume (HV) samplers were used in order to obtain more particle mass. The HV filter particles were measured with GC/MS after extraction and derivatisation. The highest concentrations were found for the sugars and the dicarboxylic acids. Four terpene acids, pinonaldehyde and isoprene oxidation products were detected. Differences between day and night samples were found for pinonaldehyde (night: 13.7 ng m −3; day: 2.7 ng m −3), for pinic acid (night: 3.2 ng m −3; day: 9.5 ng m −3) and also for the 2-methyltetrols (night: 4.0 ng m −3; day: 8 ng m −3). The detected terpene and isoprene oxidation products account only for a small part of the measured organic carbon content of particles. In all cases oxalic acid accounts for the major fraction of the speciated organic carbon. The origin of the main components like inorganic ions, OC, and EC is associated with the origin of air masses.

Observation of 2-methyltetrols and related photo-oxidation products of isoprene in boreal forest aerosols from Hyytiälä, Finland

Abstract. Oxidation products of isoprene including 2-methyltetrols (2-methylthreitol and 2-methylerythritol), 2-methylglyceric acid and triol derivatives of isoprene (2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene) have been detected in boreal forest PM1 aerosols collected at Hyytiälä, southern Finland, during a 2004 summer period, at significant atmospheric concentrations (in total 51 ng m−3 in summer versus 0.46 ng m−3 in fall). On the basis of these results, it can be concluded that photo-oxidation of isoprene is an important atmospheric chemistry process that contributes to secondary organic aerosol formation during summer in this conifer forest ecosystem. In addition to isoprene oxidation products, malic acid, which can be regarded as an intermediate in the oxidation of unsaturated fatty acids, was also detected at high concentrations during the summer period (46 ng m−3 in summer versus 5.2 ng m−3 in fall), while levoglucosan, originating from biomass burning, became relatively more important during the fall period (29 ng m−3 in fall versus 10 ng m−3 in summer). Pinic acid, a major photo-oxidation product of α-pinene in laboratory experiments, could only be detected at trace levels in the summer samples, suggesting that further oxidation of pinic acid occurs and/or that different oxidation pathways are followed. We hypothesize that photo-oxidation of isoprene may participate in the early stages of new particle formation, a phenomenon which has been well documented in the boreal forest environment.

Secondary Organic Aerosol Production from Terpene Ozonolysis. 1. Effect of UV Radiation

We report secondary organic aerosol (SOA) yields from the ozonolysis of alpha-pinene under both dark and UV-illuminated conditions. Exposure to UV light reduces SOA yield by 20-40%, with a maximum reduction in yield coinciding with a minimum in the amount of terpene consumed (15-30 ppb). The data are consistent with a constant absolute reduction in the yield of approximately 0.03. Gas chromatography mass spectrometry analysis of filter samples indicates that the major products found in alpha-pinene SOA include organic acids (e.g., pinic acid), keto acids (e.g., pinonic acid), and hydroxy keto acids (e.g., 10-hydroxypinonic acid). Analysis of filter-based results suggests that yield reduction is a result of the formation of a more volatile product distribution when experiments are conducted in the presence of UV light. These results implythat previous "dark bag" experiments may overestimate SOA generation from monoterpenes and also that SOA generation in the atmosphere may depend significantly on actinic flux.

Identification and Quantification of Aerosol Polar Oxygenated Compounds Bearing Carboxylic or Hydroxyl Groups. 2. Organic Tracer Compounds from Monoterpenes

In this study, a comparison is made of polar organic compounds found in the field with those produced in secondary organic aerosol from laboratory irradiations of natural hydrocarbons and oxides of nitrogen (NOx). The field samples comprised atmospheric particulate matter (PM2.5) collected at Research Triangle Park (RTP), NC, during the summer of 2003, and the laboratory samples originated from the photooxidation of the following monoterpenes: alpha-pinene, beta-pinene, and d-limonene. To determine the structural characteristics of the polar compounds, the filter samples were solvent extracted and derivatized using a technique based on single and multistep derivatizations. The resulting compound derivatives were analyzed by GC-MS in the methane-Cl and El modes. In addition to previously reported biogenic oxidation products (pinic acid, pinonic acid, norpinic acid, nopinone, and pinonaldehyde), seven multifunctional organic compounds were found in both field and laboratory samples. These compounds, which are proposed as possible atmospheric tracers for secondary organic aerosol from monoterpenes, were consistent with the following identifications: 3-isopropyl pentanedioic acid; 3-acetyl pentanedioic acid; 3-carboxy heptanedioic acid; 3-acetyl hexanedioic acid; 2-isopropyl-1,2-dihydroxybutanol; 4-isopropyl-2,4-dihydroxyhexanol; and 3-(2-hydroxy-ethyl)-2,2-dimethyl-cyclobutane carboxylic acid. Initial attempts have been made to quantify the concentrations of these tracer compounds on the basis of surrogate compound calibrations. The occurrence of these compounds in both laboratory and field measurements suggests that secondary organic aerosol originating from biogenic hydrocarbons are contributing to the regional aerosol burden in the southeastern United States. Several of these compounds also appear to contribute to the global aerosol burden in that they have also been identified in Europe and Brazil.

Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3

The role of organic peroxides in secondary organic aerosol (SOA) formation from reactions of monoterpenes with O3 was investigated in a series of environmental chamber experiments. Reactions were performed with endocyclic (alpha-pinene and delta3-carene) and exocyclic (beta-pinene and sabinene) alkenes in dry and humid air and in the presence of the OH radical scavengers: cyclohexane, 1-propanol, and formaldehyde. A thermal desorption particle beam mass spectrometer was used to probe the identity and volatility of SOA components, and an iodometric-spectrophotometric method was used to quantify organic peroxides. Thermal desorption profiles and mass spectra showed that the most volatile SOA components had vapor pressures similar to pinic acid and that much of the SOA consisted of less volatile species that were probably oligomeric compounds. Peroxide analyses indicated that the SOA was predominantly organic peroxides, providing evidence that the oligomers were mostly peroxyhemiacetals formed by heterogeneous reactions of hydroperoxides and aldehydes. For example, it was estimated that organic peroxides contributed approximately 47 and approximately 85% of the SOA mass formed in the alpha- and beta-pinene reactions, respectively. Reactions performed with different OH radical scavengers indicated that most of the hydroperoxides were formed through the hydroperoxide channel rather than by reactions of stabilized Criegee intermediates. The effect of the OH radical scavenger on the SOA yield was also investigated, and the results were consistent with results of recent experiments and model simulations that support a mechanism based on changes in the [HO2]/[RO2] ratios. These are the first measurements of organic peroxides in monoterpene SOA, and the results have important implications for understanding the mechanisms of SOA formation and the potential effects of atmospheric aerosol particles on the environment and human health.

Atmospheric fate of OH initiated oxidation of terpenes. Reaction mechanism of α-pinene degradation and secondary organic aerosol formation

This paper studies the reaction products of α-pinene, β-pinene, sabinene, 3-carene and limonene with OH radicals and of α-pinene with ozone using FT-IR spectroscopy for measuring gas phase products and HPLC-MS-MS to measure products in the aerosol phase. These techniques were used to investigate the secondary organic aerosol (SOA) formation from the terpenes. The gas phase reaction products were all quantified using reference compounds. At low terpene concentrations (0.9–2.1 ppm), the molar yields of gas phase reaction products were: HCHO 16–92%, HCOOH 10–54% (OH source: H 2O 2, 6–25 ppm); HCHO 127–148%, HCOOH 4–6% (OH source: CH 3ONO, 5–8 ppm). At high terpene concentrations (4.1–13.2 ppm) the results were: HCHO 9–27%, HCOOH 15–23%, CH 3(CO)CH 3 0–14%, CH 3COOH 0–5%, nopinone 24% (only from β-pinene oxidation), limona ketone 61% (only from limonene oxidation), pinonaldehyde was identified during α-pinene degradation (OH source H 2O 2, 23–30 ppm); HCHO 76–183%, HCOOH 12–15%, CH 3(CO)CH 3 0–12%, nopinone 17% (from β-pinene oxidation), limona ketone 48% (from limonene oxidation), pinonaldehyde was identified during α-pinene degradation (OH source CH 3ONO, 14–16 ppm). Pinic acid, pinonic acid, limonic acid, limoninic acid, 3-caric acid, 3-caronic acid and sabinic acid were identified in the aerosol phase. On the basis of these results, we propose a formation mechanism for pinonic and pinic acid in the aerosol phase explaining how degradation products could influence SOA formation and growth in the troposphere.

Determination of organic acids in aerosol particles from a coniferous forest by liquid chromatography–mass spectrometry

LC-MS methods with use of ion-trap and time-of-flight mass spectrometers were developed for the determination of organic acids in aerosol samples collected by a high-volume sampler in a Finnish coniferous forest. Comparison was made of the composition of samples collected during atmospheric formation of new aerosol particles and on days when this formation did not occur. A dynamic sonication-assisted solvent extraction system was developed for fast and quantitative extraction of the filter samples. Several organic acids, including pinonic acid, pinic acid, and homologous series of n-alkanoic acids, n-alkenoic acids, and aliphatic dicarboxylic acids, were identified. In samples collected between 08:00 and 16:00 hours the concentration of pinonic acid ranged from 0.5 ng m(-3) to 3.7 ng m(-3) and that of pinic acid from 0.2 ng m(-3) to 1.5 ng m(-3). For most of the compounds identified, the trends in concentration could be explained by the differences in temperature during collection. However, concentrations of short-chain n-alkanoic acids were clearly higher on the days when new aerosol particle formation occurred.

Interaction energies between aerosol precursors formed in the photo-oxidation of α-pinene

A possible first step in the formation of biogenic secondary organic aerosols involving products from the reaction of α -pinene with ozone is studied on a microscopic level. Recent research indicates that dicarboxylic acids are involved in aerosol formation in forest atmospheres but the actual mechanism is not known. It has been suggested that stable dimers between dicarboxylic acids are important for the initial formation of the aerosols. Using modern computational methods we have performed an investigation of the structures and interaction energies of a series of dimers formed by the cis-forms of pinic and norpinic acid. Interaction energies (PW91) for the most stable dimers were in the range −104.0 to −88.4 kJ mol−1.

Formation of oxidation products in a ventilation system

We have studied the formation of oxidation products from the ozonolysis of a monoterpene (α-pinene) in an authentic ventilation system. We observed ten products, norpinic acid, pinic acid, glyoxal, methyl glyoxal, norpinonic acid, pinonic acid, a C4 dicarbonyl (C4H6O2), a C5 dicarbonyl (C5H8O2), norpinon aldehyde, and pinon aldehyde. Experiments were conducted at a low (2.0 g m−3) and moderate (8 g m−3) humidity levels. All products but C4 dicarbonyl and norpinon aldehyde were detected at the low humidity level, but only glyoxal, methyl glyoxal, C4 dicarbonyl, norpinon aldehyde and pinon aldehyde were detected at a moderate humidity. Experiments were conducted at low ppb levels (75 ppb ozone and 4 and 10 ppb α-pinene) and with a short reaction time (75 s). Experiments showed that 5–6% of the α-pinene reacted, which was approximately 4–5 times more than predicted by theoretical calculations. This discrepancy suggests a significant contribution from heterogeneous reactions. These oxidation products were formed despite low reactant concentrations and a short reaction time, indicating that the formation of oxidation products likely occurs at ambient levels and in real settings.

Overview of the field measurement campaign in Hyytiälä, August 2001 in the framework of the EU project OSOA

Abstract. As part of the OSOA (Origin and formation of Secondary Organic Aerosols) project, two intensive field campaigns were conducted in Melpitz, Germany and Hyytiälä, Finland. This paper gives an overview of the measurements made during the Hyytiälä campaign, which was held between 1 and 16 August 2001. Various instrumental techniques were used to achieve physical and chemical characterisation of aerosols and to investigate possible precursor gases. During the OSOA campaign in Hyytiälä, particle formation was observed on three consecutive days at the beginning of the campaign (1 to 3 August 2001) and on three days later on. The investigation of the meteorological situation divided the campaign into two parts. During the first three days of August, relatively cold and clean air masses from northwest passed over the station (condensation sink – CS: <0.002 s-1, NOx: <0.5 ppb). Daily particle bursts of one fraction of the nucleation mode aerosols (3–10 nm) with number concentrations between 600–1200 particles cm-3 were observed. After this period, warmer and more polluted air from south-west to south-east arrived at the station (CS: 0.002–0.01 s-1, NOx: 0.5–4 ppb) and during these 13 days only three events were observed. These events were not as apparent as those that occurred during the earlier period of the campaign. The chemical analyses from different institutes of PM2, PM2.5 and PM10 particles confirmed the assumption that organic matter from the oxidation of various terpenes contributed to the formation of secondary organic aerosols (SOA). Concerning these conclusions among others, the ratio between formic (oxidation product of isoprene and monoterpenes by ozone) and acetic acid (increased by anthropogenic emissions) (ratio=1 to 1.5) and concentration of different carboxylic acids (up to 62 ngm-3) were investigated. Gas/particle partitioning of five photo-oxidation products from α- and β-pinene resulted in higher concentrations of pinonic, nor pinonic and pinic acids in the particle phase than in the gas phase, which indicates a preference to the particle phase for these compounds. The average growth factors (GF) from 100 nm particles in water vapour gave a diurnal pattern with a maximum during daytime and values between 1.2 and 1.7. On average, the amount of secondary organic carbon reached values around 19% of the sampled aerosols and we speculate that formation of SOA with the influence of photo-oxidation products from terpenes was the reason for the observed particle bursts during the campaign. However, correlations between the precursor gases or the favourable condensing species with the monitored nucleation mode particles were not found. For the investigated time period other factors like the condensation sink of newly formed particles to the pre-existing aerosols, temperature and solar irradiance seem to be more important steering parameters for the production of new aerosols. Another open question concerns the vertical distribution of the formation of SOA. For this reason measurements were conducted at different altitudes using a tethered balloon platform with particle sampling and particle counting equipment. They were incorporated with eddy covariance (EC) flux measurements made at 23 m above ground level. The results give first indications that production of new aerosols happens throughout the planetary boundary layer (PBL), whereby different parameters e.g. temperature, CS, solar irradiance or concentration of monoterpenes are responsible for the location of the vertical maximum.

Aerosol-chamber study of the α-pinene/O3 reaction: influence of particle acidity on aerosol yields and products

Abstract α -Pinene ozonolysis was carried out in the presence of ammonium sulfate or sulfuric acid seed particles in a 9 m 3 Teflon chamber at the mixing ratios of 100 ppbv for α -pinene and about 70 ppbv for ozone. The evolution of size distribution was measured by means of a differential mobility particle sizer (DMPS). The resulting secondary organic aerosol (SOA) was sampled by a denuder/quartz fiber filter combination for the determination of the total organic carbon concentration (TOC) in the particle phase, using a thermographic method and by a denuder/PTFE filter combination for the analysis of individual chemical species in the particle phase using capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS). cis -Pinic acid ( m / z 185) and another species tentatively identified at m / z 171 and 199 were the major particle phase species for both seed particles although the product yields were different, indicating the influence of seed particle acidity. A thermographic method for the determination of TOC showed an increase of particle phase organics by 40% for the experiments with higher acidity. CE-ESI-MS analysis showed a large increase in the concentration of compounds with M w >300 from the experiments with sulfuric acid seed particles. These results suggest that the seed particle acidity enhances the yield of SOA and plays an important role in the formation of larger molecules in the particle phase. Our results from direct particle phase chemical analysis suggest for the first time that condensation of smaller organics takes place by polymerization or aldol condensation following the formation of aldehydes, such as pinonaldehyde from the terpene ozonolysis.