Suppression of the phenolic SOA formation in the presence of electrolytic inorganic seed.

Phenolic compounds are largely attributed to wildfire gases and rapidly react with atmospheric oxidants to form persistent phenoxy free radicals, which influence atmospheric chemistry and secondary organic aerosol (SOA) formation. In this study, phenol or o-cresol was photochemically oxidized under various conditions (NOx levels, humidity, and seed conditions) in an outdoor photochemical reactor. Unexpectedly, SOA growth of both phenols was suppressed in the presence of salted aqueous aerosol compared to non-seed SOA. This discovery is different from the typical SOA formation of aromatic or biogenic hydrocarbons, which show noticeably higher SOA yields via organic aqueous reactions. Phenol, o-cresol, and their phenolic products (e.g., catechols) are absorbed in aqueous aerosol and form phenoxy radicals via heterogeneous reactions under sunlight. The resulting phenoxy radicals are redistributed between the gas and particle phases. Gaseous phenoxy radicals quickly react with ozone to form phenyl peroxide radicals and regenerated through a NOx cycle to retard phenol oxidation and SOA formation. The explicit oxidation mechanisms of phenol or o-cresol in the absence of aqueous phase were derived including the Master Chemical Mechanism (MCM v3.3.1) and the path for peroxy radical adducts originating from the addition of an OH radical to phenols to form low volatility products (e.g., multi-hydroxy aromatics). The resulting gas mechanisms of phenol or o-cresol were, then, applied to the Unified Partitioning Aerosol Phase Reaction (UNIPAR) model to predict SOA formation via multiphase partitioning of organics and aerosol-phase oligomerization. The model well simulated chamber-generated phenolic SOA in absence of wet-inorganic seed, but significantly overestimated SOA mass in presence of wet seed. This study suggests that heterogeneous chemistry to form phenoxy radicals needs to be included to improve SOA prediction from phenols. The suppression of atmospheric oxidation due to phenoxy radicals in wet inorganic aerosol can explain the low SOA formation during wildfire episodes.

Characterization of Atmospheric Processes of Brevetoxins in Sea Spray Aerosols from Red Tide Events.

Atmospheric processes can affect the longevity of harmful toxins in sea spray aerosols (SSA). This study characterized the degradation of brevetoxin (BTx) in SSA under different environmental conditions. The samples of seawater collected during a Karenia brevis bloom in Manasota, Florida, were nebulized into a large outdoor photochemical chamber to mimic the atmospheric oxidation of aerosolized toxins and then aged in the presence or absence of sunlight and/or O3. Aerosol samples were collected during the aging process using a Particle-Into-Liquid Sampler. Their BTx concentrations were measured using an enzyme-linked immuno-sorbent assay (ELISA) and high-performance liquid chromatography/tandem mass spectroscopy. The BTx ozonolysis rate constant measured by ELISA was 5.74 ± 0.21 × 103 M-1 s-1. The corresponding lifetime for decay of 87.5% BTx in the presence of 20 ppb of O3 was 7.08 ± 0.26 h, suggesting that aerosolized BTx can still travel long distances at night before SSA deposition. BTx concentrations in SSA decreased more rapidly in the presence of sunlight than in its absence due to oxidation with photochemically produced OH radicals.

Prediction of Phase State of Secondary Organic Aerosol Internally Mixed with Aqueous Inorganic Salts.

In the presence of inorganic salts, secondary organic aerosol (SOA) undergoes liquid-liquid phase separation (LLPS), liquid-solid phase separation, or a homogeneous phase in ambient air. In this study, a regression model was derived to predict aerosol phase separation relative humidity (SRH) for various organic and inorganic mixes. The model implemented organic physicochemical parameters (i.e., oxygen to carbon ratio, molecular weight, and hydrogen-bonding ability) and the parameters related to inorganic compositions (i.e., ammonium, sulfate, nitrate, and water). The aerosol phase data were observed using an optical microscope and also collected from the literature. The crystallization of aerosols at the effloresce RH (ERH) was semiempirically predicted with a neural network model. Overall, the greater SRH appeared for the organic compounds with the lower oxygen to carbon ratios or the greater molecular weight and the higher aerosol acidity or the larger fraction of inorganic nitrate led to the lower SRH. The resulting model has been demonstrated for three different chamber-generated SOA (originated from ß-pinene, toluene, and 1,3,5-trimethylbenzene), which were internally mixed with the inorganic aqueous system of ammonium-sulfate-water. For all three SOA systems, both observations and model predictions showed LLPS at RH <80%. In the urban atmosphere, LLPS is likely a frequent occurrence for the typical anthropogenic SOA, which originates from aromatic and alkane hydrocarbon.

Simulating the impact of gas-wall partitioning on SOA formation using the explicit gas mechanism integrated with aqueous reactions containing electrolytes.

The impact of the Teflon reactor wall on secondary organic aerosol (SOA) formation was explicitly simulated by using the Unified Partitioning Aerosol Phase Reaction (UNIPAR) model integrated with gas-wall partitioning (GWP). The formation of oxygenated semivolatile organic compounds (SVOCs) from the photooxidation of hydrocarbons (HC) was simulated by using an explicit gas-kinetic mechanism (MCM V3.3.1). In the model, SVOC's GWP and gas-particle partitioning onto preexisting particulate matter were kinetically treated with the absorption and desorption processes. The UNIPAR model streamlined aerosol growth via the oligomerization of reactive SVOCs in the organic phase and aqueous reactions in the inorganic phase. Two important GWP parameters, GWP coefficient (Kw, i) and the deposition rate constant (k_onw, i) of SVOCs (i) to the wall were predicted by using a quantitative structure activity relationship (QSAR) employing SVOCs' physicochemical descriptors. This GWP model was then incorporated with the UNIPAR model in the DSMACC-KPP platform and simulated SOA chamber data. The three different HCs (toluene, 1,3,5-trimethylbenzene, and α-pinene) were photochemically oxidized in the presence of NOx and inorganic seed aerosols in an outdoor photochemical smog chamber (UF-APHOR). The impact of GWP on SOA mass varied ranging from 9% to 71% with HCs, seed conditions, NOx, and temperature. Toluene SOA in the absence of inorganic aerosol was the most sensitive to GWP. However, in the presence of wet-inorganic seed, the impact of GWP on SOA was smaller than that of non-seed SOA owing to rapid reactions of organic species in the aqueous phase. SOA mass can be significantly underestimated in the absence of wet-inorganic seed when the aerosol model employs parameters derived using SOA data with GWP artifacts.

Differential toxicities of fine particulate matters from various sources.

Fine particulate matters less than 2.5 µm (PM2.5) in the ambient atmosphere are strongly associated with adverse health effects. However, it is unlikely that all fine particles are equally toxic in view of their different sizes and chemical components. Toxicity of fine particles produced from various combustion sources (diesel engine, gasoline engine, biomass burning (rice straw and pine stem burning), and coal combustion) and non-combustion sources (road dust including sea spray aerosols, ammonium sulfate, ammonium nitrate, and secondary organic aerosols (SOA)), which are known major sources of PM2.5, was determined. Multiple biological and chemical endpoints were integrated for various source-specific aerosols to derive toxicity scores for particles originating from different sources. The highest toxicity score was obtained for diesel engine exhaust particles, followed by gasoline engine exhaust particles, biomass burning particles, coal combustion particles, and road dust, suggesting that traffic plays the most critical role in enhancing the toxic effects of fine particles. The toxicity ranking of fine particles produced from various sources can be used to better understand the adverse health effects caused by different fine particle types in the ambient atmosphere, and to provide practical management of fine particles beyond what can be achieved only using PM mass which is the current regulation standard.

Dynamic Oxidative Potential of Atmospheric Organic Aerosol under Ambient Sunlight.

The atmospheric process dynamically changes the chemical compositions of organic aerosol (OA), thereby complicating the interpretation of its health effects. In this study, the dynamic evolution of the oxidative potential of various OA was studied, including wood combustion particles and secondary organic aerosols (SOA) generated from different hydrocarbons (i.e., gasoline, toluene, isoprene, and α-pinene). The oxidative potential of OA at different aging stages was subsequently measured by the dithiothreitol consumption (DTTm, mass normalized). We hypothesized that DTT consumptions by OA were modulated by catalytic particulate oxidizers (e.g., quinones), noncatalytic particulate oxidizers (e.g., organic hydroperoxides and peroxyacyl nitrates) and electron-deficient alkenes. The results of this study showed that the oxidative potential of OA decreased after an extended period of aging due to the decomposition of particulate oxidizers and electron-deficient alkenes. Quinones (GC-MS data) partially attributed to the DTTm of fresh wood smoke particles but rapidly dropped with aging. In biogenic SOA, organic hydroperoxides (4-nitrophenyl boronic acid assay) exclusively accounted for DTTm and decreased with aging. The DTTm of aromatic SOA, mainly comprising organic hydroperoxides and electron-deficient alkenes (FTIR data), was shortly elevated during the early atmospheric process; however, it showed a noticeable decrease (32-75%) for a long period of aging. We concluded that fresh or moderately aged OA are more reactive to a sulfhydryl group than highly aged OA.

Heterogeneous Photo-oxidation of SO2 in the Presence of Two Different Mineral Dust Particles: Gobi and Arizona Dust.

The impact of authentic mineral dust particles sourced from the Gobi Desert (GDD) on the kinetic uptake coefficient of SO2 was studied under varying environments (humidity, O3, and NOx) using both an indoor chamber and an outdoor chamber. There was a significant increase in the kinetic uptake coefficient of SO2 (γSO42-,light) for GDD particles under UV light compared to the value (γSO42-,dark) under dark conditions at various relative humidities (RH) ranging from 20% to 80%. In both the presence and the absence of O3 and NOx, γSO42-,light and γSO42-,dark greatly increased with increasing RH. The resulting γSO42-,light of GDD particles was also compared to that of Arizona Test Dust (ATD) particles. The γSO42-,light values of GDD were 2 to 2.5 times greater than those of ATD for all RH levels. To understand the photocatalytic act of dust particles, both GDD and ATD were characterized for the metal element composition of fresh particles, the aerosol acidity of aged particles, and the hygroscopic properties of both fresh and aged particles. We conclude that the difference in the formation of sulfate between GDD and ATD particles is regulated mainly by the quantity of the semiconductive metals in dust particles and partially by hygroscopic properties.

Prediction of delivery of organic aerosols onto air-liquid interface cells in vitro using an electrostatic precipitator.

To better characterize biological responses to atmospheric organic aerosols, the efficient delivery of aerosol to in vitro lung cells is necessary. In this study, chamber generated secondary organic aerosol (SOA) entered the commercialized exposure chamber (CULTEX® Radial Flow System Compact) where it interfaced with an electrostatic precipitator (ESP) (CULTEX® Electrical Deposition Device) and then deposited on a particle collection plate. This plate contained human lung cells (BEAS-2B) that were cultured on a membrane insert to produce an air-liquid interface (ALI). To augment in vitro assessment using the ESP exposure device, the particle dose was predicted for various sampling parameters such as particle size, ESP deposition voltage, and sampling flowrate. The dose model was evaluated against the experimental measured mass of collected airborne particles. The high flowrate used in this study increased aerosol dose but failed to achieve cell stability. For example, RNA in the ALI BEAS-2B cells in vitro was stable at 0.15L/minute but decayed at high flowrates. The ESP device and the resulting model were applied to in vitro studies (i.e., viability and IL-8 expression) of toluene SOA using ALI BEAS-2B cells with a flowrate of 0.15L/minute, and no cellular RNA decay occurred.

The SOA formation model combined with semiempirical quantum chemistry for predicting UV-Vis absorption of secondary organic aerosols.

A new model for predicting the UV-visible absorption spectra of secondary organic aerosols (SOA) has been developed. The model consists of two primary parts: a SOA formation model and a semiempirical quantum chemistry method. The mass of SOA is predicted using the PHRCSOA (Partitioning Heterogeneous Reaction Consortium Secondary Organic Aerosol) model developed by Cao and Jang [Environ. Sci. Technol., 2010, 44, 727]. The chemical composition is estimated using a combination of the kinetic model (MCM) and the PHRCSOA model. The absorption spectrum is obtained by taking the sum of the spectrum of each SOA product calculated using a semiempirical NDDO (Neglect of Diatomic Differential Overlap)-based method. SOA was generated from the photochemical reaction of toluene or α-pinene at different NO(x) levels (low NO(x): 24-26 ppm, middle NO(x): 49 ppb, high NO(x): 104-105 ppb) using a 2 m(3) indoor Teflon film chamber. The model simulation reasonably agrees with the measured absorption spectra of α-pinene SOA but underestimates toluene SOA under high and middle NO(x) conditions. The absorption spectrum of toluene SOA is moderately enhanced with increasing NO(x) concentrations, while that of α-pinene SOA is not affected. Both measured and calculated UV-visible spectra show that the light absorption of toluene SOA is much stronger than that of α-pinene SOA.

Amorphous silica coatings on magnetic nanoparticles enhance stability and reduce toxicity to in vitro BEAS-2B cells.

BACKGROUND: Nanoparticles are being rapidly assimilated into numerous research fields and consumer products. A concurrent increase in human exposure to such materials is expected. Magnetic nanoparticles (MNPs) possess unique and beneficial features, increasing their functionality and integrative potential. However, MNP toxicity characterization is limited, especially in regards to the human respiratory system. This study aimed to assess the in vitro effects of airborne MNPs on BEAS-2B cells. Uncoated iron oxide was compared with two amorphous silica-coated MNPs, hypothesizing the coatings reduced toxicity and increased particle stability. METHOD: BEAS-2B cells were cultured at an air-liquid interface and exposed to airborne MNPs using a fabricated exposure device. Indices of cytotoxicity, inflammatory response, oxidative stress, and iron homeostasis were monitored postexposure via cell viability assays and qRT-PCR. Concentrations of soluble iron-associated with different MNPs were also examined before and after contact with several aqueous organic and inorganic acids. RESULTS: The silica-coated MNPs had reduced soluble iron concentrations. This result indicates that the silica coating provides a barrier to and prevents the mobilization of soluble iron from the particle to the cell, thereby reducing the risk of oxidative stress or alterations of iron homeostasis. Cells exposed to MagSilica50 and MagSilica50-85® showed little to no indications of cytotoxicity or induction of inflammatory response/oxidative stress at the examined delivery concentrations. CONCLUSION: MNPs coated with amorphous silica are protected from acidic erosion. Correspondingly, the particle stability translates into reduced cytotoxicity and cellular influence on human airway epithelial cells.

The effects of active chlorine on photooxidation of 2-methyl-2-butene.

Active chlorine comprising hypochlorite (OCl⁻), hypochlorous acid (HOCl) and chlorine (Cl2) is the active constituent in bleach formulations for a variety of industrial and consumer applications. However, the strong oxidative reactivity of active chlorine can cause adverse effects on both human health and the environment. In this study, aerosolized Oxone® [2KHSO5, KHSO4, K2SO4] with saline solution has been utilized to produce active chlorine (HOCl and Cl2). To investigate the impact of active chlorine on volatile organic compound (VOC) oxidation, 2-methyl-2-butene (MB) was photoirradiated in the presence of active chlorine using a 2-m³ Teflon film indoor chamber. The resulting carbonyl products produced from photooxidation of MB were derivatized with O-(2,3,4,5,6-pentafluorobenzyl) hydroxyamine hydrochloride (PFBHA) and analyzed using gas chromatograph-ion trap mass spectrometer (GC/ITMS). The photooxidation of MB in the presence of active chlorine was simulated with an explicit kinetic model using a chemical solver (Morpho) which included both Master Chemical Mechanism (MCM) and Cl radical reactions. The reaction rate constants of a Cl radical with MB and its oxidized products were estimated using a Structure-Reactivity Relationship method. Under dark conditions no effect of active chlorine on MB oxidation was apparent, whereas under simulated daylight conditions (UV irradiation) rapid MB oxidation was observed due to photo-dissociation of active chlorine. The model simulation agrees with chamber data showing rapid production of oxygenated products that are characterized using GC/ITMS. Ozone formation was enhanced when MB was oxidized in the presence of irradiated active chlorine and NO(x).

An SOA model for toluene oxidation in the presence of inorganic aerosols.

A predictive model for secondary organic aerosol (SOA) formation including both partitioning and heterogeneous reactions is explored for the SOA produced from the oxidation of toluene in the presence of inorganic seed aerosols. The predictive SOA model comprises the explicit gas-phase chemistry of toluene, gas-particle partitioning, and heterogeneous chemistry. The resulting products from the explicit gas phase chemistry are lumped into several classes of chemical species based on their vapor pressure and reactivity for heterogeneous reactions. Both the gas-particle partitioning coefficient and the heterogeneous reaction rate constant of each lumped gas-phase product are theoretically determined using group contribution and molecular structure-reactivity. In the SOA model, the predictive SOA mass is decoupled into partitioning (OM(P)) and heterogeneous aerosol production (OM(H)). OM(P) is estimated from the SOA partitioning model developed by Schell et al. (J. Geophys. Res. 2001, 106, 28275-28293 ) that has been used in a regional air quality model (CMAQ 4.7). OM(H) is predicted from the heterogeneous SOA model developed by Jang et al. (Environ. Sci. Technol. 2006, 40, 3013-3022 ). The SOA model is evaluated using a number of the experimental SOA data that are generated in a 2 m(3) indoor Teflon film chamber under various experimental conditions (e.g., humidity, inorganic seed compositions, NO(x) concentrations). The SOA model reasonably predicts not only the gas-phase chemistry, such as the ozone formation, the conversion of NO to NO(2), and the toluene decay, but also the SOA production. The model predicted that the OM(H) fraction of the total toluene SOA mass increases as NO(x) concentrations decrease: 0.73-0.83 at low NO(x) levels and 0.17-0.47 at middle and high NO(x) levels for SOA experiments with high initial toluene concentrations. Our study also finds a significant increase in the OM(H) mass fraction in the SOA generated with low initial toluene concentrations, compared to those with high initial toluene concentrations. On average, more than a 1-fold increase in OM(H) fraction is observed when the comparison is made between SOA experiments with 40 ppb toluene to those with 630 ppb toluene. Such an observation implies that heterogeneous reactions of the second-generation products of toluene oxidation can contribute considerably to the total SOA mass under atmospheric relevant conditions.

Acid and organic aerosol coatings on magnetic nanoparticles increase iron concentrations in human airway epithelial cells.

Numerous industrial applications for man-made nanoparticles have been proposed. Interactions of nanoparticles with agents in the atmosphere may impact human health. We tested the postulate that in vitro exposures of respiratory epithelial cells to airborne magnetic nanoparticles (MNP; Fe(3)O(4)) with and without a secondary organic aerosol (SOA) and an inorganic acid could affect iron homeostasis, oxidative stress, and interleukin (IL)-8 release. Cell iron concentrations were increased after exposures to MNP and values were further elevated with co-exposures to either SOA or inorganic acid. Increased expression of ferritin and elevated levels of RNA for DMT1, proteins for iron storage and transport respectively, followed MNP exposures, but values were significant for only those with co-exposures to inorganic acid and organic aerosols. Cell iron concentration corresponded to a measure of oxidative stress in the airway epithelial cells; MNP with co-exposures to SOA and inorganic acid increased both available metal and indices of oxidant generation. Finally, the release of a proinflammatory cytokine (i.e. IL-8) by the exposed cells similarly increased with cell iron concentration. We conclude that MNP can interact with a SOA and an inorganic acid to present metal in a catalytically reactive state to cultured respiratory cells. This produces an oxidative stress to affect a release of IL-8.

Deposition of magnetic nanoparticles suspended in the gas phase on a specific target area.

Magnetic nanoparticles (MNPs) suspended in the air were delivered onto a specific area under a magnetic field. The targeting efficiency and the collected mass of MNPs were studied for various physical parameters such as MNP concentrations, the MNP size, sampling flow, and the strength of magnetic field. A model to predict the delivery of MNPs onto a specific target area was developed for both stagnant air and horizontal air streams and demonstrated for experimental observations. Overall, the theoretically predicted targeting mass of MNPs reasonably agreed with experimental observations. The potential use of the resulting targeting method using the MNPs suspended in the air has been also explored for the delivery of secondary organic aerosols (SOAs) to a specific area. SOAs are created from ozonolysis of terpenes coated on preexisting MNPs and targeted using the device under horizontal air streams.

Exposure of BEAS-2B cells to secondary organic aerosol coated on magnetic nanoparticles.

Toxicological investigation suggests that exposures to complex secondary organic aerosol (SOA) products can result in adverse health effects in biological systems. However, the mechanism of adverse health effects is not yet understood. One of the major restrictions in studies of health effects of SOA is a particle exposure technique. In this study, we applied an innovative soft targeting technology using magnetic nanoparticles (MNP) to deliver SOAs onto target biological systems under a magnetic field. The exploratory exposure technology using MNP was demonstrated for the SOAs created from the reaction of ozone with alpha-pinene in an indoor Teflon film chamber. SOA increased the release of the proinflammatory mediator interleukin-8 by respiratory epithelial cells. These results support that MNP can effectively deliver SOAs to epithelial cells in vitro resulting in a significant biological effects.

SOA formation from partitioning and heterogeneous reactions: model study in the presence of inorganic species.

A predictive model for secondary organic aerosol (SOA) formation by both partitioning and heterogeneous reactions was developed for SOA created from ozonolysis of alpha-pinene in the presence of preexisting inorganic seed aerosols. SOA was created in a 2 m3 polytetrafluoroethylene film indoor chamber under darkness. Extensive sets of SOA experiments were conducted varying humidity, inorganic seed compositions comprising of ammonium sulfate and sulfuric acid, and amounts of inorganic seed mass. SOA mass was decoupled into partitioning (OM(P)) and heterogeneous aerosol production (OM(H)). The reaction rate constant for OM(H) production was subdivided into three categories (fast, medium, and slow) to consider different reactivity of organic products for the particle phase heterogeneous reactions. The influence of particle acidity on reaction rates was treated in a previous semiempirical model. Model OM(H) was developed with medium and strong acidic seed aerosols, and then extrapolated to OM(H) in weak acidic conditions, which are more relevant to atmospheric aerosols. To demonstrate the effects of preexisting glyoxal derivatives (e.g., glyoxal hydrate and dimer) on OM(H), SOA was created with a seed mixture comprising of aqueous glyoxal and inorganic species. Our results show that heterogeneous SOA formation was also influenced by preexisting reactive glyoxal derivatives.

Semiempirical model for organic aerosol growth by acid-catalyzed heterogeneous reactions of organic carbonyls.

Aerosol growth by heterogeneous reactions of diverse carbonyls in the presence and absence of acidified seed aerosols was studied in a 4 m long flow reactor (2.5 cm i.d.) and a 2-m3 indoor Teflon film chamber under darkness. The acid catalytic effects on heterogeneous aerosol production were observed for diverse carbonyls in various ranges of humidities and compositions of seed inorganic aerosols. Particle population data measured by a scanning mobility particle sizer were used to calculate organic aerosol growth. To accountforthe aerosol growth contributed by heterogeneous reactions, the increase in organic aerosol mass was normalized bythe organic mass predicted by partitioning or the square of predicted organic mass. The carbonyl heterogeneous reactions were accelerated in the presence of acid catalysts (H2SO4), leading to higher aerosol yields than in their absence. The experimental data from aerosol yields in the flow reactorwere semiempirically fitted to the model parameters to predict the organic aerosol growth. The model parameters consist of environmental characteristics and molecular structure information of organic carbonyls. Basicity constants of carbonyls were used to describe the proton affinity of carbonyls for the acid catalysts. Particle environmental factors, such as humidity, temperature, and inorganic seed composition, were expressed by excess acidity and the parameters obtained from an inorganic thermodynamic model. A stepwise regression analysis of the aerosol growth model for the experimental data revealed that either the chemical structure information of carbonyls or characteristic environmental parameters are statistically significant in the prediction of organic aerosol growth. It was concluded thatthis model approach is applicable to predict secondary organic aerosol formation by heterogeneous reaction.

Atmospheric organic aerosol production by heterogeneous acid-catalyzed reactions.

Exploratory evidence from our laboratories shows that acidic surfaces on atmospheric aerosols lead to very real and potentially multifold increases in secondary organic aerosol (SOA) mass and build-up of stabilized nonvolatile organic matter as particles age. One possible explanation for these heterogeneous processes are the acid-catalyzed (e.g., H2SO4 and HNO3) reactions of atmospheric multifunctional organic species (e.g., multifunctional carbonyl compounds) that are accommodated onto the particle phase from the gas phase. Volatile organic hydrocarbons (VOCs) from biogenic sources (e.g., terpenoids) and anthropogenic sources (aromatics) are significant precursors for multifunctional organic species. The sulfur content of fossil fuels, which is released into the atmosphere as SO2, results in the formation of secondary inorganic acidic aerosols or indigenous acidic soot particles (e.g., diesel soot). The predominance of SOAs contributing to PM2.5 (particulate matter, that is, 2.5 microm or smaller than 2.5 microm), and the prevalence of sulfur in fossil fuels suggests that interactions between these sources could be considerable. This study outlines a systematic approach for exploring the fundamental chemistry of these particle-phase heterogeneous reactions. If acid-catalyzed heterogeneous reactions of SOA products are included in next-generation models, the predicted SOA formation will be much greater and have a much larger impact on climate-forcing effects than we now predict. The combined study of both organic and inorganic acids will also enable greater understanding of the adverse health effects in biological pulmonary organs exposed to particles.

Photochemical products in urban mixtures enhance inflammatory responses in lung cells.

Complex urban air mixtures that realistically mimic urban smog can be generated for investigating adverse health effects. "Smog chambers" have been used for over 30 yr to conduct experiments for developing and testing photochemical models that predict ambient ozone (O(3)) concentrations and aerosol chemistry. These chambers were used to generate photochemical and nonirradiated systems, which were interfaced with an in vitro exposure system to compare the inflammatory effects of complex air pollutant mixtures with and without sunlight-driven chemistry. These are preliminary experiments in a new project to study the health effects of particulate matter and associated gaseous copollutants. Briefly, two matched outdoor chambers capable of using real sunlight were utilized to generate two test atmospheres for simultaneous exposures to cultured lung cells. One chamber was used to produce a photochemically active system, which ran from sunrise to sunset, producing O(3) and the associated secondary products. A few hours after sunset, NO was added to titrate and remove completely the O(3), forming NO(2). In the second chamber, an equal amount of NO(2) and the same amount of the 55-component hydrocarbon mixture used to setup the photochemical system in the first side were injected. A549 cells, from an alveolar type II-like cell line grown on membranous support, were exposed to the photochemical mixture or the "original" NO(2)/hydrocarbon mixture for 5 h and analyzed for inflammatory response (IL-8 mRNA levels) 4 h postexposure. In addition, a variation of this experiment was conducted to compare the photochemical system producing O(3) and NO(2), with a simple mixture of only the O(3) and NO(2). Our data suggest that the photochemically altered mixtures that produced secondary products induced about two- to threefold more IL-8 mRNA than the mixture of NO(2) and hydrocarbons or O(3). These results indicate that secondary products generated through the photochemical reactions of NO(x) and hydrocarbons may significantly contribute to the inflammatory responses induced by exposure to urban smog. From previous experience with relevant experiments, we know that many of these gaseous organic products would contribute to the formation of significant secondary organic particle mass in the presence of seed particles (including road dust or combustion products). In the absence of such particles, these gaseous products remained mostly as gases. These experiments show that photochemically produced gaseous products do influence the toxic responses of the cells in the absence of particles.

Formation of oligomers in secondary organic aerosol.

The formation of oligomeric molecules, an important step in secondary organic aerosol production, is reported. Aerosols were produced by the reaction of alpha-pinene and ozone in the presence of acid seed aerosol and characterized by exact mass measurements and tandem mass spectrometry. Oligomeric products between 200 and 900 u were detected with both electrospray ionization and matrix-assisted laser desorption ionization. The exact masses and dissociation products of these ions were consistent with various combinations of the known primary products of this reaction ("monomers") with and/or without the expected acid-catalyzed decomposition products of the monomers. Oligomers as large as tetramers were detected. Both aldol condensations and gem-diol reactions are suggested as possible pathways for oligomer formation. Exact mass measurements also revealed reaction products that cannot be explained by simple oligomerization of monomers and monomer decomposition products, suggesting the existence of complex reaction channels. Chemical reactions leading to oligomer formation provide a reasonable answer to a difficult problem associated with secondary organic aerosol production in the atmosphere. It is unlikely that monomers alone play an important role in the formation and growth of nuclei in the atmosphere as their Kelvin vapor pressures are too high for them to significantly partition into the particle phase. Polymerization provides a mechanism by which partitioning to the particle phase becomes favored.