Secondary Organic Aerosol Growth Research Articles

Coupled CFD analysis of size distributions on indoor secondary organic aerosol derived from ozone/limonene reactions

Recently, theoretical analysis and experiment have been initiated to investigate the generation of secondary organic aerosols (SOA) by chemical reactions in indoor air. In particular, it has been confirmed that SOA are generated by the reaction of ozone with various terpenoids. The overarching goal of this work was to better understand ozone, VOC (volatile organic compounds) and generated SOA distributions within rooms. We carried out cylindrical test chamber experiments to measure SOA generation from the chemical reaction of ozone and limonene and discussed numerical models to describe it. In this paper, we propose a method for predicting the particle size distribution of SOA generated by ozone and limonene chemical reactions in air. In particular, we discuss an analytical method that involves a sectional modeling approach governing equations of SOA. Although the changes in particle size distribution in a 40-section model were reproduced to a certain extent, rigorous modeling for the generation and growth of SOA and an increased number of sections are needed for improvement of prediction accuracy.

Gas phase precursors to anthropogenic secondary organic aerosol: detailed observations of 1,3,5-trimethylbenzene photooxidation

Abstract. A series of photooxidation experiments were conducted in an atmospheric simulation chamber in order to investigate the oxidation mechanism and secondary organic aerosol (SOA) formation potential of the model anthropogenic gas phase precursor, 1,3,5-trimethylbenzene. Alongside specific aerosol measurements, comprehensive gas phase measurements, primarily by Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), were carried out to provide detailed insight into the composition and behaviour of the organic components of the gas phase matrix during SOA formation. An array of gas phase organic compounds was measured during the oxidation process, including several previously unmeasured primary bicyclic compounds possessing various functional groups. Analysis of results obtained during this study implies that these peroxide bicyclic species along with a series of ring opening products and organic acids contribute to SOA growth. The effect of varying the VOC/NOx ratio on SOA formation was explored, as was the effect of acid seeding. It was found that low NOx conditions favour more rapid aerosol formation and a higher aerosol yield, a result that implies a role for organic peroxides in the nucleation process and SOA growth.

Secondary organic aerosols from ozone-initiated reactions with emissions from wood-based materials and a “green” paint

This study examined the formation and growth of secondary organic aerosols (SOA) generated when ozone was added to a 1 m 3 glass chamber that contained either pine shelving, oriented strand board (OSB), beech boards, or beach boards painted with an “eco” paint. The experiments were conducted at close to real-world conditions; the chamber was ventilated at ∼0.5 air changes/h; the loadings (exposed surface of building materials to chamber volume) were in the range of 1–2.5 m 2 m −3; and the initial O 3 concentrations were between 15 and 40 ppb. Throughout each experiment particles were measured with both a condensation nuclei counter and an optical counter, while terpenes were measured before and after the ozone exposure period using sorbent tubes. The pine boards emitted primarily α-pinene and 3-carene and lesser amounts of 5 other terpenes; when O 3 was introduced, the particle counts increased dramatically; the mass concentration reached ∼15 μg m −3 at ∼20 ppb O 3, and ∼95 μg m −3 at ∼40 ppb O 3. The OSB emitted primarily limonene and α-pinene. Although the particle counts increased when O 3 was introduced, the increase was not as large as anticipated based on the terpene concentrations. The beech boards emitted negligible quantities of terpenes, and the introduction of O 3 resulted in almost no increase in the particle concentration. Beech boards painted with an “eco” paint emitted large amounts of limonene and lesser amounts of carvone; upon introduction of O 3 the particle counts increased sharply with the mass concentration reaching ∼20 μg m −3 at ∼15 ppb O 3 and ∼160 μg m −3 at ∼35 ppb O 3. These experiments demonstrate that the emission of terpenes and potential generation of SOA varies greatly among different types of wood and pressed wood materials. In the case of the pine boards and painted beech boards, the SOA concentrations generated at modest O 3 concentrations approach or exceed current guideline levels for PM 2.5 established by the US EPA and the World Health Organization.

Reactions of Semivolatile Organics and Their Effects on Secondary Organic Aerosol Formation

Secondary organic aerosol (SOA) constitutes a significant fraction of total atmospheric particulate loading, but there is evidence that SOA yields based on laboratory studies may underestimate atmospheric SOA. Here we present chamber data on SOA growth from the photooxidation of aromatic hydrocarbons, finding that SOA yields are systematically lower when inorganic seed particles are not initially present. This indicates that concentrations of semivolatile oxidation products are influenced by processes beyond gas-particle partitioning, such as chemical reactions and/or loss to chamber walls. Predictions of a kinetic model in which semivolatile compounds may undergo reactions in both the gas and particle phases in addition to partitioning are qualitatively consistent with the observed seed effect, as well as with a number of other recently observed features of SOA formation chemistry. The behavior arises from a kinetic competition between uptake to the particle phase and reactive loss of the semivolatile product. It is shown that when hydrocarbons react in the absence of preexisting organic aerosol, such loss processes may lead to measured SOA yields lower than would occur under atmospheric conditions. These results underscore the need to conduct studies of SOA formation in the presence of atmospherically relevant aerosol loadings.

Effects of seed aerosols on the growth of secondary organic aerosols from the photooxidation of toluene

Hydroxyl radical (.OH)-initiated photooxidation reaction of toluene was carried out in a self-made smog chamber. Four individual seed aerosols such as ammonium sulfate, ammonium nitrate, sodium silicate and calcium chloride, were introduced into the chamber to assess their influence on the growth of secondary organic aerosols (SOA). It was found that the low concentration of seed aerosols might lead to high concentration of SOA particles. Seed aerosols would promote rates of SOA formation at the start of the reaction and inhibit its formation rate with prolonging the reaction time. In the case of ca. 9000 pt/cm 3 seed aerosol load, the addition of sodium silicate induced a same effect on the SOA formation as ammonium nitrate. The influence of the four individual seed aerosols on the generation of SOA decreased in the order of calcium chloride>sodium silicate and ammonium nitrate>ammonium sulfate.

Effect of particle phase oligomer formation on aerosol growth

We study theoretically the effect of oligomer formation on secondary organic aerosol (SOA) growth following ozonolysis of α -pinene. Our goal is to show qualitatively, using a simplified condensational growth model, that the formation of involatile oligomers can induce the condensation growth of aerosols even if the secondary organic species formed in the oxidation reactions are rather volatile and therefore poorly condensable. The closed system studied consists of a single effective gas-phase oxidation product, and a seed aerosol population consisting of monodisperse ammonium sulphate particles. The oligomer formation is described as an effective dimerisation reaction between the monomers in the aerosol phase. By varying the dimerisation constant until our model results match the results from earlier smog-chamber studies, we are able to make order-of-magnitude estimations of the unknown dimerisation rates needed to induce the observed SOA growth. We also make model simulations using atmospheric α -pinene and ozone concentrations, and find that the effective dimerisation rate inducing SOA growth in the atmosphere has to be considerably higher than that causing SOA growth in smog-chamber conditions.

Contribution of First- versus Second-Generation Products to Secondary Organic Aerosols Formed in the Oxidation of Biogenic Hydrocarbons

Biogenic hydrocarbons emitted by vegetation are important contributors to secondary organic aerosol (SOA), but the aerosol formation mechanisms are incompletely understood. In this study, the formation of aerosols and gas-phase products from the ozonolysis and photooxidation of a series of biogenic hydrocarbons (isoprene, 8 monoterpenes, 4 sesquiterpenes, and 3 oxygenated terpenes) are examined. By comparing aerosol growth (measured by Differential Mobility Analyzers, DMAs) and gas-phase concentrations (monitored by a Proton Transfer Reaction Mass Spectrometer, PTR-MS), we study the general mechanisms of SOA formation. Aerosol growth data are presented in terms of a "growth curve", a plot of aerosol mass formed versus the amount of hydrocarbon reacted. From the shapes of the growth curves, it is found that all the hydrocarbons studied can be classified into two groups based entirely on the number of double bonds of the hydrocarbon, regardless of the reaction systems (ozonolysis or photooxidation) and the types of hydrocarbons studied: compounds with only one double bond and compounds with more than one double bond. For compounds with only one double bond, the first oxidation step is rate-limiting, and aerosols are formed mainly from low volatility first-generation oxidation products; whereas for compounds with more than one double bond, the second oxidation step may also be rate-limiting and second-generation products contribute substantially to SOA growth. This behavior is characterized by a vertical section in the growth curve, in which continued aerosol growth is observed even after all the parent hydrocarbon is consumed.

Chamber studies of secondary organic aerosol growth by reactive uptake of simple carbonyl compounds

Recent experimental evidence indicates that heterogeneous chemical reactions play an important role in the gas‐particle partitioning of organic compounds, contributing to the formation and growth of secondary organic aerosol in the atmosphere. Here we present laboratory chamber studies of the reactive uptake of simple carbonyl species (formaldehyde, octanal, trans,trans‐2,4‐hexadienal, glyoxal, methylglyoxal, 2,3‐butanedione, 2,4‐pentanedione, glutaraldehyde, and hydroxyacetone) onto inorganic aerosol. Gas‐phase organic compounds and aqueous seed particles (ammonium sulfate or mixed ammonium sulfate/sulfuric acid) are introduced into the chamber, and particle growth and composition are monitored using a differential mobility analyzer and an Aerodyne Aerosol Mass Spectrometer. No growth is observed for most carbonyls studied, even at high concentrations (500 ppb to 5 ppm), in contrast with the results from previous studies. The single exception is glyoxal (CHOCHO), which partitions into the aqueous aerosol much more efficiently than its Henry's law constant would predict. No major enhancement in particle growth is observed for the acidic seed, suggesting that the large glyoxal uptake is not a result of particle acidity but rather of ionic strength of the seed. This increased partitioning into the particle phase still cannot explain the high levels of glyoxal measured in ambient aerosol, indicating that additional (possibly irreversible) pathways of glyoxal uptake may be important in the atmosphere.

The bi-directional exchange of oxygenated VOCs between a loblolly pine (<I>Pinus taeda</I>) plantation and the atmosphere

Abstract. Using new in-situ field observations of the most abundant oxygenated VOCs (methanol, acetaldehyde, acetone, C3/C4 carbonyls, MVK+MAC and acetic acid) we were able to constrain emission and deposition patterns above and within a loblolly pine (Pinus taeda) plantation with a sweetgum (Liquidambar styraciflua) understory. During the day canopy scale measurements showed significant emission of methanol and acetone, while methyl vinyl ketone and methacrolein, acetaldehyde and acetic acid were mainly deposited during the day. All oxygenated compounds exhibited strong losses during the night that could not be explained by conventional dry deposition parameterizations. Accompanying leaf level measurements indicated substantial methanol and acetone emissions from loblolly pine. The exchange of acetaldehyde was more complex. Laboratory measurements made on loblolly pine needles indicated that acetaldehyde may be either emitted or taken up depending on ambient concentrations, with the compensation point increasing exponentially with temperature, and that mature needles tended to emit more acetaldehyde than younger needles. Canopy scale measurements suggested mostly deposition. Short-term (approx. 2 h) ozone fumigation in the laboratory had no detectable impact on post-exposure emissions of methanol and acetone, but decreased the exchange rates of acetaldehyde. The emission of a variety of oxygenated compounds (e.g. carbonyls and alcohols) was triggered or significantly enhanced during laboratory ozone fumigation experiments. These results suggest that higher ambient ozone levels in the future might enhance the biogenic contribution of some oxygenated compounds. Those with sufficiently low vapor pressures may potentially influence secondary organic aerosol growth. Compounds recently hypothesized to be primarily produced in the canopy atmosphere via ozone plus terpenoid-type reactions can also originate from the oxidation reaction of ozone with leaf surfaces and inside the leaf. This needs to be taken into account when scaling up very reactive biogenic compounds.

Hygroscopic behavior of partially volatilized coastal marine aerosols using the volatilization and humidification tandem differential mobility analyzer technique

Coastal marine nucleation, Aitken, and accumulation mode aerosol particles with back trajectories indicative of marine origin were examined using a volatilization and humidification tandem differential mobility analyzer (VHTDMA) to reveal the volatilization temperatures of the various component species. The diameter hygroscopic growth factors of the residue particles were continually examined throughout the volatilization process. In each of the three modes the dominant particle type appeared to be composed of the same four physicochemically distinct species though in different ratios. These species exhibited volatility and hygroscopic behavior consistent with combinations of a volatile organic species, sulfuric acid, ammonium sulfate or bisulfate, iodine oxide, and an insoluble nonvolatile residue. The Aitken and accumulation mode aerosols contain large fractions of the insoluble, volatile, organic‐like material, and the volatilization of this species results in a distinct increase in the water volume uptake of the particles. Of the four distinct species, only the sulfuric acid‐like species constituted an increasing volume fraction with decreasing particle size. This finding indicates that nucleation mode particles constitute an acidic seed and as such would undergo acid‐catalyzed secondary organic aerosol growth at a faster rate. The lack of a nonvolatile hygroscopic residue consistent with sea salt in these particles implies that the aerosolization of seawater is not the dominant production mechanism for these submicrometer coastal marine aerosols.

Representation of Secondary Organic Aerosol Laboratory Chamber Data for the Interpretation of Mechanisms of Particle Growth

Absorptive models of gas-particle partitioning have been shown to be successful in describing the formation and growth of secondary organic aerosol (SOA). Here the expression for particle growth derived by Odum et al. (Odum, J. R.; Hoffmann, T.; Bowman, F.; Collins, D.; Flagan, R. C.; Seinfeld, J. H. Gas/particle partitioning and secondary organic aerosol yields. Environ. Sci. Technol. 1996, 30, 2580-2585) is extended to facilitate interpretation of SOA growth data measured in the laboratory in terms of the underlying chemistry, even when details of the reactions are not well-constrained. A simple (one-component) expression for aerosol growth (deltaM) as a function of the amount of hydrocarbon reacted (deltaHC) is derived, and the effects of changes to three key parameters, stoichiometric yield of condensable species, gas-particle partitioning coefficient, and concentration of preexisting aerosol, are discussed. Two sets of laboratory chamber data on SOA growth are examined in this context: the ozonolysis of alpha-pinene and the OH-initiated photooxidation of aromatic compounds. Even though these two systems have a number of significant differences, both are described well within this framework. From the shapes of the deltaM versus deltaHC curves in each case, the importance of poorly constrained chemistry such as heterogeneous reactions and gas-phase reactions of oxidation products is examined.

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.

Simulating the Formation of Secondary Organic Aerosol from the Photooxidation of Aromatic Hydrocarbons

Environmental Context. Atmospheric particulate material can affect the radiative balance of the atmosphere and is believed to be detrimental to human health. Secondary organic aerosols (SOA), which make a significant contribution to the total atmospheric burden of fine particulate material, are formed in situ following the photochemical transformation of organic pollutants into relatively less-volatile, oxygenated compounds which can subsequently transfer from the gas phase to a particle phase. SOA formation from the atmospheric photooxidation of aromatic hydrocarbons—present, for example, as a result of automobile use—is believed to be important in the urban environment and yet the mechanisms are not well understood. For example, even the reasons for observed variations in the relative propensity for SOA formation, from the photooxidation of various simple aromatic hydrocarbons, are not clear. Abstract. The formation and composition of secondary organic aerosol (SOA) from the photooxidation of benzene, p-xylene, and 1,3,5-trimethylbenzene has been simulated using the Master Chemical Mechanism version 3.1 (MCM v3.1) coupled to a representation of the transfer of organic material from the gas to particle phase. The combined mechanism was tested against data obtained from a series of experiments conducted at the European Photoreactor (EUPHORE) outdoor smog chamber in Valencia, Spain. Simulated aerosol mass concentrations compared reasonably well with the measured SOA data only after absorptive partitioning coefficients were increased by a factor of between 5 and 30. The requirement of such scaling was interpreted in terms of the occurrence of unaccounted-for association reactions in the condensed organic phase leading to the production of relatively more nonvolatile species. Comparisons were made between the relative aerosol forming efficiencies of benzene, toluene, p-xylene, and 1,3,5-trimethylbenzene, and differences in the OH-initiated degradation mechanisms of these aromatic hydrocarbons. A strong, nonlinear relationship was observed between measured (reference) yields of SOA and (proportional) yields of unsaturated dicarbonyl aldehyde species resulting from ring-fragmenting pathways. This observation, and the results of the simulations, is strongly suggestive of the involvement of reactive aldehyde species in association reactions occurring in the aerosol phase, thus promoting SOA formation and growth. The effect of NOx concentrations on SOA formation efficiencies (and formation mechanisms) is discussed.

Indoor Fine Particles: The Role of Terpene Emissions from Consumer Products

Consumer products can emit significant quantities of terpenes, which can react with ozone (O3). Resulting byproducts include compounds with low vapor pressures that contribute to the growth of secondary organic aerosols (SOAs). The focus of this study was to evaluate the potential for SOA growth, in the presence of O3, following the use of a lime-scented liquid air freshener, a pine-scented solid air freshener, a lemon-scented general-purpose cleaner, a wood floor cleaner, and a perfume. Two chamber experiments were performed for each of these five terpene-containing agents, one at an elevated O3 concentration and the other at a lower O3 concentration. Particle number and mass concentrations increased and O3 concentrations decreased during each experiment. Experiments with terpene-based air fresheners produced the highest increases in particle number and mass concentrations. The results of this study clearly demonstrate that homogeneous reactions between O3 and terpenes from various consumer products can lead to increases in fine particle mass concentrations when these products are used indoors. Particle increases can occur during periods of elevated outdoor O3 concentrations or indoor O3 generation, coupled with elevated terpene releases. Human exposure to fine particles can be reduced by minimizing indoor terpene concentrations or O3 concentrations.

Simulating the Formation of Secondary Organic Aerosol from the Photooxidation of Toluene

Environmental Context. Atmospheric particulate material can affect climate by absorbing and scattering solar radiation and by altering the properties of clouds. They are also implicated as a health risk. Secondary organic aerosol (SOA) material makes an important contribution to this particulate burden. SOA material results from the transfer of gas-phase species into a particle state after the formation of products from the reaction of atmospheric volatile organic compounds (VOCs) with oxygen. SOA from the oxidation of aromatic hydrocarbons, such as toluene, a gasoline fuel component, is important in the polluted urban environment and yet formation mechanisms are not well understood. Abstract. The formation and composition of secondary organic aerosol (SOA) from the gas-phase photooxidation of toluene has been simulated using the Master Chemical Mechanism version 3.1 (MCM v3.1) coupled to a representation of the transfer of organic material from the gas phase to a particle phase. The mechanism was tested against data from a series of toluene photooxidation experiments performed at the European Photoreactor (EUPHORE) outdoor smog chamber in Valencia, Spain. Simulated aerosol mass concentrations compared reasonably well with the measured SOA data after absorptive partitioning coefficients were increased by a factor of between 20 and 80, although the simulated onset of SOA growth was delayed with respect to the experiments. A simplified representation of peroxyhemiacetal adduct formation, from the reaction of organic hydroperoxides with aldehydes in the condensed organic phase, was included in the mechanism and this reduced the required scaling of partitioning coefficients and reduced the time-lag in simulated SOA growth. These observations, and the dependence of SOA formation efficiency upon the initial NO concentration, strongly imply the significant occurrence of association reactions in the condensed organic phase and the important role of organic hydroperoxides in SOA formation. Aerosol data from photooxidation experiments of intermediate degradation products (butenedial, 4-oxo-pentenal, and ortho-cresol) were also simulated using the developed mechanism.

Effect of acidic seed on biogenic secondary organic aerosol growth

Abstract Secondary organic aerosol (SOA) growth in the presence of acid aerosols was studied in twin 500 l Teflon bags and in a 4 m flow reactor. In Teflon bags, isoprene, acrolein and α-pinene were all made to react individually with ozone and exposed to either acid or non-acid inorganic seed aerosols to determine the effect of acid-catalyzed heterogeneous reactions on SOA growth. α-Pinene and ozone were made to react in a flow reactor to assess the immediate effect of mixing an acid aerosol with SOA at high and low relative humidity levels. In all cases, exposure to acid seed aerosol increased the amount of SOA mass produced. Fourier transform infrared spectra of the SOA in acid systems confirmed the transformation of carbonyl functional groups through acid-catalyzed heterogeneous reactions when SOAs formed in acidic environments or were exposed to acidic aerosols. Organic products initially produced from ozonation in the gas phase partition onto the inorganic seed aerosol and react heterogeneously with an acid catalyst forming low vapor pressure products. These acid-catalyzed heterogeneous reactions are implicated in generating the increased SOA mass observed in acidic aerosol systems as they transform predominantly gas phase compounds of high volatility into low vapor pressure predominantly particle phase products.