Myoseon Jang

Newly characterized products and composition of secondary aerosols from the reaction of α-pinene with ozone

Secondary aerosols from the reaction of α-pinene with ozone were generated in a 190 m3 outdoor Teflon chamber, and products of these aerosols were characterized. Products were separated by gas chromatography and detected with electron-impact mass spectrometry, chemical-impact mass spectrometry, and Fourier transform infrared spectrometry. Because products from the reaction of α-pinene with ozone contain oxidized functional groups such as carboxylic acids and carbonyls, these products are poorly resolved by standard gas chromatography. To use standard chromatographic techniques, derivatization of oxidized functional groups was necessary. Carbonyl products were derivatized with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride and carboxylic acids with pentafluorobenzyl bromide. The major identified products were nor-pinonic acid, pinonic acid, 2,2-dimethylcyclobutane-1,3-dicarboxylic acid, pinic acid, and pinonaldehyde. Dicarboxylic acids have lower vapor pressures than either their corresponding di-aldehydes or mono-acids, and have only recently been identified in α-pinene–ozone aerosols. Given their comparatively low vapor pressures, diacids contribute significantly to the aerosol formation process from the reaction of α-pinene with ozone. The composition of these secondary aerosols is strongly influenced by temperature. During the summer experiments, the aerosol composition is dominated by diacids. During the cooler winter experiments, the di-carbonyl and carbonyl-acid products also contributed to the aerosol composition.

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 (O3) 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 O3 and the associated secondary products. A few hours after sunset, NO was added to titrate and remove completely the O3, forming NO2. In the second chamber, an equal amount of NO2 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” NO2/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 O3 and NO2, with a simple mixture of only the O3 and NO2. 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 NO2 and hydrocarbons or O3. These results indicate that secondary products generated through the photochemical reactions of NOx 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.

Benz[a]anthracene photodegradation in the presence of known organic constituents of atmospheric aerosols.

Benz[a]anthracene photodegradation rates in toluene solutions containing co-solutes were compared using a photochemical turntable reactor. Each co-solute investigated was found at relatively high concentrations in atmospheric particulate matter. Benz-[a]anthracene photodegradation was accelerated by the presence of 9,10-anthraquinone, xanthone, 2-furaldehyde, 2,4-dimethylbenzaldehyde, 9,10-phenanthrenequinone, 2-acetylfuran, and furfuryl alcohol. Decay was inhibited by 7-benzanthrone. Other compounds had little or no effect on benz[a]-anthracene decay. Possible photochemical reaction mechanisms are discussed, and it is concluded that several competing mechanisms may be responsible, including electronic energytransferfollowed by reaction from the triplet state, singlet oxygen attack, and radical chain reactions initiated by hydrogen abstraction of aerosol constituents. The results suggest that particle organic composition can strongly influence polycyclic aromatic hydrocarbon photodegradation rates in atmospheric aerosols.

An approach to studying the effect of organic composition on atmospheric aerosol photochemistry

Physical and chemical characteristics of atmospheric carbonaceous aerosol particles are reviewed, and their likely effects on the particulate matter as a reaction medium are discussed. An approach to studying the effects of organic components of atmospheric particulate matter on aerosol organic photochemistry based on this discussion is described. Available information suggests that atmospheric aerosols from common combustion sources, such as wood smoke or diesel soot, are almost entirely carbonaceous, consisting of a relatively thick, possibly liquid organic layer coating an elemental carbon core. This implies that organic compounds are fairly mobile and consequently that overall organic composition of an atmospheric aerosol could play an important role in the photochemical behavior of associated reactive organic substances. In accordance with this a photochemical turntable reactor was used to investigate the effects of organic aerosol constituents dissolved in an organic solvent, using benz[a]anthracene as a model photochemically reactive compound. Preliminary results showed that 4 out of 10 major organic compound classes found in atmospheric aerosols include compounds which accelerated benz[a]anthracene photodegradation. These were methoxyphenols, polycyclic aromatic ketones and quinones, substituted benzaldehydes, and substituted furans.

Gas–particle partitioning of semi-volatile organics on organic aerosols using a predictive activity coefficient model: analysis of the effects of parameter choices on model performance

Abstract The partitioning of a diverse set of semivolatile organic compounds (SOCs) on a variety of organic aerosols was studied using smog chamber experimental data. Existing data on the partitioning of SOCs on aerosols from wood combustion, diesel combustion, and the α-pinene-O3 reaction was augmented by carrying out smog chamber partitioning experiments on aerosols from meat cooking, and catalyzed and uncatalyzed gasoline engine exhaust. Model compositions for aerosols from meat cooking and gasoline combustion emissions were used to calculate activity coefficients for the SOCs in the organic aerosols and the Pankow absorptive gas/particle partitioning model was used to calculate the partitioning coefficient Kp and quantitate the predictive improvements of using the activity coefficient. The slope of the log K p vs. log p L 0 correlation for partitioning on aerosols from meat cooking improved from −0.81 to −0.94 after incorporation of activity coefficients i γ om . A stepwise regression analysis of the partitioning model revealed that for the data set used in this study, partitioning predictions on α-pinene-O3 secondary aerosol and wood combustion aerosol showed statistically significant improvement after incorporation of i γ om , which can be attributed to their overall polarity. The partitioning model was sensitive to changes in aerosol composition when updated compositions for α-pinene-O3 aerosol and wood combustion aerosol were used. The octanol–air partitioning coefficients (KOA) effectiveness as a partitioning correlator over a variety of aerosol types was evaluated. The slope of the log K p − log K OA correlation was not constant over the aerosol types and SOCs used in the study and the use of KOA for partitioning correlations can potentially lead to significant deviations, especially for polar aerosols.

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.

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.

Role of sea salt aerosols in the formation of aromatic secondary organic aerosol: yields and hygroscopic properties

Environmental context In the coastal and ocean environment, oil spills and ship movement can produce hazardous, organic aerosols. In this study, the role of sea salt in the formation processes of crude-oil-derived organic aerosols derived was explored, and it was found that sea salt can greatly increase the formation and growth of these toxic aerosols. Understanding of this process is crucial for evaluating the effect of oil spills and ship movements on air quality and human health. Abstract Dual, large (52m3), outdoor chambers were used to investigate the effect of aerosol aqueous phase chemistry on the secondary organic aerosol (SOA) yields of the photooxidation products of aromatic hydrocarbons in the coastal environment. Toluene and 1,3,5-trimethylbenzene were photochemically oxidised in the presence and absence of inorganic seeds (sea salt aerosol (SSA) or NaCl) at low NOx conditions. Overall, the presence of SSA, which was shown to contain water even at low relative humidities (RHs), led to higher SOA yields than the presence of NaCl seeds and the seedless condition. The results suggest that SOA yields in the coastal environment will be higher than those produced in terrestrial environment. To study the effect of SOA formation on the chemical composition of SSA, inorganic species were measured using a particle-into-liquid-sampler coupled to an ion chromatograph. The hygroscopic properties of the SSA internally mixed with SOA were analysed using a Fourier-transform infrared spectrometer. The fresh SSA shows a weak phase transition whereas no clear phase transition appeared in the aged SSA. The depletion of Cl– due to the accommodation of nitric acid and carboxylic acids on the surface of SSA coincides with changes in aerosol hygroscopic properties.

Partitioning of semivolatile organic compounds in the presence of a secondary organic aerosol in a controlled atmosphere

The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid α-pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.

Colorimetric Particle Acidity Analysis of Secondary Organic Aerosol Coating on Submicron Acidic Aerosols

The particle acidity of secondary organic aerosol (SOA) created from ozonolysis of α-pinene in the presence of acidic inorganic seed aerosols was investigated using an indoor Teflon film chamber. Colorimetry integrated with a reflectance UV-Visible spectrometer was used for the first time to dynamically measure the aerosol acidity over time. An external calibration curve was produced based on the correlation between the proton mass (ng) collected on the filter, which was impregnated with metanil yellow, and the absorbance of the reflectance UV-Visible spectra for the protonated and the unprotonated metanil yellow on the filter. Using this calibration curve, the particle acidity of the submicron acidic sulfate aerosol coated with SOA was measured from the reflectance UV-Visible spectra of filter samples. The colorimetric analysis requires a short sampling time (less than 2 m) for SOA studies using the laboratory Teflon film chamber and eliminates extraction of the filter sample with water. Results show that the particle acidity of the aerosol decreased over time due to the formation of organic sulfate through the interaction of sulfuric acid with SOA products. The feasibility of this method is also demonstrated for the measurement of the acidity of ambient particles.