Secondary Organic Aerosol Particles Research Articles

Development and characterization of an exposure generation system to investigate the health effects of particles from fresh and aged traffic emissions

Atmospheric photochemical reactions of vehicular primary emissions result in the formation of secondary organic aerosol (SOA). This is the first study that has investigated the toxicity of secondary particles based on fleet vehicular emissions. We developed methods for photochemical oxidation of traffic primary emissions to produce mixtures of primary and/or secondary particles suitable for animal exposures. The exposure generation system produced test atmospheres of primary (P), aged primary plus SOA (P + SOA), or SOA particles suitable for animal exposures. The system consists of (1) a sampling system to extract the traffic emissions from the plenum of a highway tunnel ventilation stack, (2) a photochemical chamber to simulate atmospheric aging, and (3) a nonselective diffusion denuder to remove gaseous pollutants prior to exposure. In the presence of traffic primary particles (P + SOA), a longer mean residence time resulted in a higher SOA yield. Higher baseline plenum primary particle mass concentration resulted in lower SOA yield. In the absence of primary particles (SOA), higher plenum gas concentrations resulted in higher SOA yield. Secondary aerosol was largely organic but contained some nitrate and sulfate. Formation of secondary aerosol is influenced significantly by reaction of primary gases with ·OH. The system (1) provides adequate flow and stable chamber output of P, P + SOA, and SOA for characterization and animal exposures and (2) generates reproducible exposure atmospheres of P, P + SOA, and SOA, all at consistent mass concentrations.

Effect of ammonia on ozone-initiated formation of indoor secondary products with emissions from cleaning products

Biogenic volatile organic compounds (BVOCs) emitted from cleaning products and air fresheners indoors are prone to oxidation resulting in the formation of secondary pollutants that can pose health risks on residents. Ammonia (NH3) is ubiquitous in ambient and indoor environments. In this study, we investigated the effect of ammonia (NH3) on secondary pollutants formation from the ozonolysis of BVOCs emitted from cleaning products including floor cleaner (FC), kitchen cleaner (KC) and dishwashing detergent (DD) in a large environmental chamber. Our results demonstrated that the presence of NH3 (maximum concentration is 240 ppb) could significantly enhance secondary organic aerosols (SOAs) formation from the ozonolysis of all the three categories of cleaning products. For example, for the FC sample, the maximum total particle concentration was up to 2.0 × 104 # cm−3 in the presence of NH3, while it was 1.3 × 104 # cm−3 which was 35% lower without NH3. However, it was found that the extent of NH3 effect on SOAs formation from the ozonolysis of BVOCs emissions was component-dependent. The presence of NH3 in the reaction systems could increase the consumptions of d-limonene that is the dominant BVOC species as identified in cleaning products. The percent yields (%) of secondary carbonyl compounds generated from the ozonolysis of BVOCs emitted from three categories of cleaning products were identified in the presence and absence of NH3, respectively. The increase in SOAs particle number concentration can be attributed to the formation of condensable salts from reactions between NH3 and organic compounds generated from the BVOCs ozonolysis processes. By investigating the NH3 effect on the ozonolysis of BVOCs mixtures in contrast to the chemistry of individual compounds, a better assessment can be made of the overall impact cleaning products have on real indoor environments.

Size distribution and chemical composition of secondary organic aerosol formed from Cl-initiated oxidation of toluene

Secondary organic aerosol (SOA) formed from Cl-initiated oxidation of toluene was investigated in a home-made smog chamber. The size distribution and chemical composition of SOA particles were measured using aerodynamic particle sizer spectrometer and the aerosol laser time-of-flight mass spectrometer (ALTOFMS), respectively. According to a large number of single aerosol diameter and mass spectra, the size distribution and chemical composition of SOA were obtained statistically. Experimental results showed that SOA particles created by Cl-initiated oxidation of toluene is predominantly in the form of fine particles, which have diameters less than 2.5 μm (i.e., PM2.5), and glyoxal, benzaldehyde, benzyl alcohol, benzoquinone, benzoic acid, benzyl hydroperoxide and benzyl methyl nitrate are the major products components in the SOA. The possible reaction mechanisms leading to these products are also proposed.

Compromise between ventilation, filtration strategies and recirculation rates for the design and operation of air-conditioned facilities in the tropics

This study examines the impact of filtration, ventilation and recirculation rate on concentration of condensed-phase, ozone (of outdoor origin)-derived oxidation products (secondary organic aerosols (SOA)) in a model room with a ventilation system that recirculates a large percentage (90%) of its supply air. Additionally, it critically evaluates the potential approach for filtering recirculated air and also avoiding the negative consequence of having loaded filters in a ventilation system. Increased recirculation rate not only influences the surface removal rate constant, but also increases the fraction of pollutants removed by building filters. Increased ventilation rate dilutes pollutants with indoor sources and ozone-derived products. Activated carbon filters are more effective in reducing ozone and SOA particles than filters without carbon. Even a filter with a quarter of the standard carbon content of the commercially available bag-type stand-alone combination filter incorporating activated carbon improves the perceived air quality significantly more than a filter without carbon. This study is important because it provides information on how to improve the health and comfort of indoor environment inhabitants without compromising on energy conservation.

Chemical ionisation mass spectrometry for the measurement of atmospheric amines

Environmental contextAmines are of interest to atmospheric chemistry as they may be important gas-phase precursors for secondary aerosol formation. We describe a mass spectrometer for real-time in-situ measurements of gaseous alkyl amines in the atmosphere. This measurement technique will help to evaluate the contribution of amines to the formation of secondary aerosols, including secondary organic aerosol and new particle formation. AbstractWe describe a chemical ionisation mass spectrometer (CIMS) for the ambient measurement of amines, known as important gas-phase precursors for secondary aerosol formation. Protonated ethanol or acetone ions were used as ionisation reagents to selectively detect high proton affinity base compounds (e.g. amines and NH3), thereby minimising interferences from other atmospheric gaseous organic compounds. With ethanol as ionisation reagent (~3 × 105 Hz of ion signals), the CIMS showed similar sensitivities (2.1–8.7 Hz pptv–1) and detection limits (7–41 pptv with a 1-min integration time) for NH3 and several atmospherically relevant key amine compounds containing one to six carbon atoms (C1- to C6-amines and their isomers). The CIMS background signals of the six amines ranged from 9 to 40 pptv, much lower than ~930 pptv for NH3. The CIMS response times were between 13 and 26 s for these amines. The unique combination of the fast time response, high sensitivities and low detection limits allows the use of this CIMS for real time measurements of atmospheric trace amines. During the ambient measurement made in Kent, OH, in November 2011, the measured mixing ratios of C2- and C3-amines were 8 ± 3 (mean ± 1 standard deviation) and 16 ± 7 pptv, whereas those of NH3 were 517 ± 259 pptv.

Mass Spectrometry Study of OH-initiated Photooxidation of Toluene

The composition of products formed from photooxidation of the aromatic hydrocarbon toluene was investigated. The OH-initiated photooxidation experiments were conducted by irradiating toluene/CH3ONO/NO/air mixtures in a smog chamber, the gaseous products were detected under the supersonic beam conditions by utilizing vacuum ultraviolet photoionization mass spectrometer using synchrotron radiation in real-time. And an aerosol time-of-flight mass spectrometer was used to provide on-line measurements of the individual secondary organic aerosol particle resulting from irradiating toluene. The experimental results demonstrated that there were some differences between the gaseous products and that of particle-phase, the products of glyoxal, 2-hydroxyl-3-oxo-butanal, nitrotoluene, and methyl-nitrophenol only existed in the particle-phase. However, furane, methylglyoxal, 2-methylfurane, benzaldehyde, cresol, and benzoic acid were the predominant photooxidation products in both the gas phase and particle phase.

Can forest trees compensate for stress-generated growth losses by induced production of volatile compounds?

Plants produce a variety of volatile organic compounds (VOCs). Under abiotic and biotic stresses, the number and amount of produced compounds can increase. Due to their long life span and large size, trees can produce biogenic VOCs (BVOCs) in much higher amounts than many other plants. It has been suggested that at cellular and tree physiological levels, induced production of VOCs is aimed at improving plant resistance to damage by reactive oxygen species generated by multiple abiotic stresses. In the few reported cases when biosynthesis of plant volatiles is inhibited or enhanced, the observed response to stress can be attributed to plant volatiles. Reported increase, e.g., in photosynthesis has mostly ranged between 5 and 50%. A comprehensive model to explain similar induction of VOCs under multiple biotic stresses is not yet available. As a result of pathogen or herbivore attack on forest trees, the induced production of VOCs is localized to the damage site but systemic induction of emissions has also been detected. These volatiles can affect fungal pathogens and the arrival rate of herbivorous insects on damaged trees, but also act as signalling compounds to maintain the trophic cascades that may improve tree fitness by improved efficiency of herbivore natural enemies. On the forest scale, biotic induction of VOC synthesis and release leads to an amplified flow of BVOCs in atmospheric reactions, which in atmospheres rich in oxides of nitrogen (NOx) results in ozone formation, and in low NOx atmospheres results in oxidation of VOCs, removal in ozone from the troposphere and the resulting formation of biogenic secondary organic aerosol (SOA) particles. I will summarize recent advances in the understanding of stress-induced VOC emissions from trees, with special focus on Populus spp. Particular importance is given to the ecological and atmospheric feedback systems based on BVOCs and biogenic SOA formation.

Volatility and hygroscopicity of aging secondary organic aerosol in a smog chamber

Abstract. The evolution of secondary organic aerosols (SOA) during (photo-)chemical aging processes was investigated in a smog chamber. Fresh SOA from ozonolysis of 10 to 40 ppb α-pinene was formed followed by aging with OH radicals. The particles' volatility and hygroscopicity (expressed as volume fraction remaining (VFR) and hygroscopicity parameter κ) were measured in parallel with a volatility and hygroscopicity tandem differential mobility analyzer (V/H-TDMA). An aerosol mass spectrometer (AMS) was used for the chemical characterization of the aerosol. These measurements were used as sensitive parameters to reveal the mechanisms possibly responsible for the changes in the SOA composition during aging. A change of VFR and/or κ during processing of atmospheric aerosols may occur either by addition of SOA mass (by condensation) or by a change of SOA composition leading to different aerosol properties. The latter may occur either by heterogeneous reactions on the surface of the SOA particles, by condensed phase reactions like oligomerization or by an evaporation – gas-phase oxidation – recondensation cycle. The condensation mechanism showed to be dominant when there is a substantial change in the aerosol mass by addition of new molecules to the aerosol phase with time. Experiments could be divided into four periods based on the temporal evolution (qualitative changes) of VFR, κ and organic mass: O3 induced condensation, ripening, and OH induced chemical aging first with substantial mass gain and then without significant mass gain. During the O3 induced condensation the particles' volatility decreased (increasing VFR) while the hygroscopicity increased. Thereafter, in the course of ripening volatility continued to decrease, but hygroscopicity stayed roughly constant. After exposing the SOA to OH radicals an OH induced chemical aging with substantial mass gain started resulting in the production of at least 50 % more SOA mass. This new SOA mass was highly volatile and oxidized. This period was then followed by further OH induced chemical aging without significant mass gain leading to a decrease of volatility while hygroscopicity and SOA mass stayed roughly constant.

Contrasting organic aerosol particles from boreal and tropical forests during HUMPPA-COPEC-2010 and AMAZE-08 using coherent vibrational spectroscopy

Abstract. We present the vibrational sum frequency generation spectra of organic particles collected in a boreal forest in Finland and a tropical forest in Brazil. These spectra are compared to those of secondary organic material produced in the Harvard Environmental Chamber. By comparing coherent vibrational spectra of a variety of terpene and olefin reference compounds, along with the secondary organic material synthesized in the environmental chamber, we show that submicron aerosol particles sampled in Southern Finland during HUMPPA-COPEC-2010 are composed to a large degree of material similar in chemical composition to synthetic α-pinene-derived material. For material collected in Brazil as part of AMAZE-08, the organic component is found to be chemically complex in the coarse mode but highly uniform in the fine mode. When combined with histogram analyses of the isoprene and monoterpene abundance recorded during the HUMPPA-COPEC-2010 and AMAZE-08 campaigns, the findings presented here indicate that if air is rich in monoterpenes, submicron-sized secondary aerosol particles that form under normal OH and O3 concentration levels can be described in terms of their hydrocarbon content as being similar to α-pinene-derived model secondary organic aerosol particles. If the isoprene concentration dominates the chemical composition of organic compounds in forest air, then the hydrocarbon component of secondary organic material in the submicron size range is not simply well-represented by that of isoprene-derived model secondary organic aerosol particles but is more complex. Throughout the climate-relevant size range of the fine mode, however, we find that the chemical composition of the secondary organic particle material from such air is invariant with size, suggesting that the particle growth does not change the chemical composition of the hydrocarbon component of the particles in a significant way.

An Investigation of the Effects of Environmental Factors on Secondary Organic Aerosol (SOA) Formation

To understand the effects of environmental factors, such as the light intensity, reaction time, the concentration of reactant on the growth of secondary organic aerosol is very important. This paper investigated the effect of environmental factors on SOA formation from biogenic volatile organic compounds (BVOCs), results show that SOA formed from OH-initiated photooxidation of BVOCs is predominantly in the form of fine particles, which have diameters less than 2.5 µm. This paper also highlighted that both the number and mass concentration of SOA particles were increasing with the prolonging of the radiation time, the increasing of light intensity, and the increasing of the reactant concentrations. The results could provide useful information to infer possible emission sources of atmospheric particles in future field measurement.

Laboratory studies of the chemical composition and cloud condensation nuclei (CCN) activity of secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA)

Abstract. Secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA) were produced in laboratory experiments from the oxidation of fourteen precursors representing atmospherically relevant biogenic and anthropogenic sources. The SOA and OPOA particles were generated via controlled exposure of precursors to OH radicals and/or O3 in a Potential Aerosol Mass (PAM) flow reactor over timescales equivalent to 1–20 days of atmospheric aging. Aerosol mass spectra of SOA and OPOA were measured with an Aerodyne aerosol mass spectrometer (AMS). The fraction of AMS signal at m/z = 43 and m/z = 44 (f43, f44), the hydrogen-to-carbon (H/C) ratio, and the oxygen-to-carbon (O/C) ratio of the SOA and OPOA were obtained, which are commonly used to characterize the level of oxidation of oxygenated organic aerosol (OOA). The results show that PAM-generated SOA and OPOA can reproduce and extend the observed f44–f43 composition beyond that of ambient OOA as measured by an AMS. Van Krevelen diagrams showing H/C ratio as a function of O/C ratio suggest an oxidation mechanism involving formation of carboxylic acids concurrent with fragmentation of carbon-carbon bonds. Cloud condensation nuclei (CCN) activity of PAM-generated SOA and OPOA was measured as a function of OH exposure and characterized as a function of O/C ratio. CCN activity of the SOA and OPOA, which was characterized in the form of the hygroscopicity parameter κorg, ranged from 8.4×10−4 to 0.28 over measured O/C ratios ranging from 0.05 to 1.42. This range of κorg and O/C ratio is significantly wider than has been previously obtained. To first order, the κorg-to-O/C relationship is well represented by a linear function of the form κorg = (0.18±0.04) ×O/C + 0.03, suggesting that a simple, semi-empirical parameterization of OOA hygroscopicity and oxidation level can be defined for use in chemistry and climate models.

Bounce behavior of freshly nucleated biogenic secondary organic aerosol particles

Abstract. The assessment of the climatic impacts and adverse health effects of atmospheric aerosol particles requires detailed information on particle properties. However, very limited information is available on the morphology and phase state of secondary organic aerosol (SOA) particles. The physical state of particles greatly affects particulate-phase chemical reactions, and thus the growth rates of newly formed atmospheric aerosol. Thus verifying the physical phase state of SOA particles gives new and important insight into their formation, subsequent growth, and consequently potential atmospheric impacts. According to our recent study, biogenic SOA particles produced in laboratory chambers from the oxidation of real plant emissions as well as in ambient boreal forest atmospheres can exist in a solid phase in size range >30 nm. In this paper, we extend previously published results to diameters in the range of 17–30 nm. The physical phase of the particles is studied by investigating particle bounce properties utilizing electrical low pressure impactor (ELPI). We also investigate the effect of estimates of particle density on the interpretation of our bounce observations. According to the results presented in this paper, particle bounce clearly decreases with decreasing particle size in sub 30 nm size range. The comparison measurements by ammonium sulphate and investigation of the particle impaction velocities strongly suggest that the decreasing bounce is caused by the differences in composition and phase of large (diameters greater than 30 nm) and smaller (diameters between 17 and 30 nm) particles.

Secondary organic aerosol formation from the photooxidation of isoprene, 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene under high NO<sub>x</sub> conditions

Abstract. Secondary organic aerosol (SOA) formation from atmospheric oxidation of isoprene has been the subject of multiple studies in recent years; however, reactions of other conjugated dienes emitted from anthropogenic sources remain poorly understood. SOA formation from the photooxidation of isoprene, isoprene-1-13C, 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene is investigated for high NOx conditions. The SOA yield measured in the 1,3-butadiene/NOx/H2O2 irradiation system (0.089–0.178) was close to or slightly higher than that measured with isoprene under similar NOx conditions (0.077–0.103), suggesting that the photooxidation of 1,3-butadiene is a possible source of SOA in urban air. In contrast, a very small amount of SOA particles was produced in experiments with 2,3-dimethyl-1,3-butadiene. Off-line liquid chromatography – mass spectrometry analysis revealed that the signals of oligoesters comprise a major fraction (0.10–0.33) of the signals of the SOA products observed from all dienes investigated. The oligoesters originate from the unsaturated aldehyde gas phase diene reaction products; namely, semi-volatile compounds produced by the oxidation of the unsaturated aldehyde undergo particle-phase oligoester formation. Oligoesters produced by the dehydration reaction between nitrooxypolyol and 2-methylglyceric acid monomer or its oligomer were also characterized in these experiments with isoprene as the starting diene. These oligomers are possible sources of the 2-methyltetrols found in ambient aerosol samples collected under high NOx conditions. Furthermore, in low-temperature experiments also conducted in this study, the SOA yield measured with isoprene at 278 K was 2–3 times as high as that measured at 300 K under similar concentration conditions. Although oligomerization plays an important role in SOA formation from isoprene photooxidation, the observed temperature dependence of SOA yield is largely explained by gas/particle partitioning of semi-volatile compounds.

Investigating the use of secondary organic aerosol as seed particles in simulation chamber experiments

Abstract. The use of β-caryophyllene secondary organic aerosol particles as seeds for smog chamber simulations has been investigated. A series of experiments were carried out in the Manchester photochemical chamber as part of the Aerosol Coupling in the Earth System (ACES) project to study the effect of seed particles on the formation of secondary organic aerosol (SOA) from limonene photo-oxidation. Rather than use a conventional seed aerosol containing ammonium sulfate or diesel particles, a method was developed to use in-situ chamber generated seed particles from β-caryophyllene photo-oxidation, which were then diluted to a desired mass loading (in this case 4–13 μg m−3). Limonene was then introduced into the chamber and oxidised, with the formation of SOA seen as a growth in the size of oxidised organic seed particles from 150 to 325 nm mean diameter. The effect of the partitioning of limonene oxidation products onto the seed aerosol was assessed using aerosol mass spectrometry during the experiment and the percentage of m/z 44, an indicator of degree of oxidation, increased from around 5 to 8 %. The hygroscopicity of the aerosol also changed, with the growth factor for 200 nm particles increasing from less than 1.05 to 1.25 at 90 % RH. The detailed chemical composition of the limonene SOA could be extracted from the complex β-caryophyllene matrix using two-dimensional gas chromatography (GC × GC) and liquid chromatography coupled to mass spectrometry. High resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS) was used to determine exact molecular formulae of the seed and the limonene modified aerosol. The average O:C ratio was seen to increase from 0.32 to 0.37 after limonene oxidation products had condensed onto the organic seed.

Enhancement effect of relative humidity on the formation and regional respiratory deposition of secondary organic aerosol

In this study, we investigated the effect of relative humidity (RH) on the formation of secondary organic aerosol (SOA) generated from the ozonolysis of d-limonene in an environmental chamber. The mass yield and the number concentration of SOA increased seven and eight times, respectively, when the RH increased from 18% to 82%. The measured total loss rates (apparent loss rates) of the number and mass concentration of SOA in the chamber ranged from 1.70 to 1.77 h −1 and from 2.51 to 2.61 h −1, respectively, at a controlled ventilation rate of 0.72 ± 0.04 h −1. The wall-deposition-loss-rate coefficient observed (1.00 ± 0.02 h −1) was approximate to the estimated value based on Zhao and Wu's model [1] which includes the factors of turbulence, Brownian diffusion, turbophoresis and surface roughness. According to the ICRP (International Commission on Radiological Protection) model, the inhaled SOA particles are deposited primarily in the alveoli of the lung. The integrated alveolar deposited dose of the mass (surface area) of SOA over 3 h accounted for 74.0–74.8% (74.3–74.9%) of the total deposited dose at the investigated RH. Raising the RH resulted in the growth of SOA particle sizes and increment of the deposition dose but did not cause significant changes in the ratio of regional to the total respiratory deposition of SOA.

Hydrogen peroxide generation from α- and β-pinene and toluene secondary organic aerosols

Abstract In-particle reactions and reactivity may play a role in aerosol aging as well as health effects associated with airborne particles. One of the main hypotheses for the species causing the observed health effects are reactive oxygen species including hydrogen peroxide (H2O2). Secondary organic aerosol (SOA), the focus of this study, comprises a major fraction of ambient fine mode particle mass. SOA were generated via dark ozonolysis of α-pinene and β-pinene, as well as photochemical oxidation of α-pinene, β-pinene, and toluene. SOA particles generate a considerable amount of H2O2 in the aqueous phase. For the same particle mass, α-pinene and β-pinene SOA have higher H2O2 generation ability than toluene SOA. H2O2 levels were sensitive to the pH of the particle extraction solutions, decreasing as the pH was increased. SOA samples aged for 20 h in room air lost a significant fraction of the H2O2 compared to fresh samples. The H2O2 is likely from decomposition or hydrolysis of hydroxyhydroperoxides, peroxic acids and related species for α- and β-pinene SOA, and from redox cycling of quinoid compounds for toluene SOA. This study provides the first quantitative measurement of H2O2 for a range of SOA particle types.

Characterization of aerosol photooxidation flow reactors: heterogeneous oxidation, secondary organic aerosol formation and cloud condensation nuclei activity measurements

Abstract. Motivated by the need to develop instrumental techniques for characterizing organic aerosol aging, we report on the performance of the Toronto Photo-Oxidation Tube (TPOT) and Potential Aerosol Mass (PAM) flow tube reactors under a variety of experimental conditions. The PAM system was designed with lower surface-area-to-volume (SA/V) ratio to minimize wall effects; the TPOT reactor was designed to study heterogeneous aerosol chemistry where wall loss can be independently measured. The following studies were performed: (1) transmission efficiency measurements for CO2, SO2, and bis(2-ethylhexyl) sebacate (BES) particles, (2) H2SO4 yield measurements from the oxidation of SO2, (3) residence time distribution (RTD) measurements for CO2, SO2, and BES particles, (4) aerosol mass spectra, O/C and H/C ratios, and cloud condensation nuclei (CCN) activity measurements of BES particles exposed to OH radicals, and (5) aerosol mass spectra, O/C and H/C ratios, CCN activity, and yield measurements of secondary organic aerosol (SOA) generated from gas-phase OH oxidation of m-xylene and α-pinene. OH exposures ranged from (2.0 ± 1.0) × 1010 to (1.8 ± 0.3) × 1012 molec cm−3 s. Where applicable, data from the flow tube reactors are compared with published results from the Caltech smog chamber. The TPOT yielded narrower RTDs. However, its transmission efficiency for SO2 was lower than that for the PAM. Transmission efficiency for BES and H2SO4 particles was size-dependent and was similar for the two flow tube designs. Oxidized BES particles had similar O/C and H/C ratios and CCN activity at OH exposures greater than 1011 molec cm−3 s, but different CCN activity at lower OH exposures. The O/C ratio, H/C ratio, and yield of m-xylene and α-pinene SOA was strongly affected by reactor design and operating conditions, with wall interactions seemingly having the strongest influence on SOA yield. At comparable OH exposures, flow tube SOA was more oxidized than smog chamber SOA, possibly because of faster gas-phase oxidation relative to particle nucleation. SOA yields were lower in the TPOT than in the PAM, but CCN activity of flow-tube-generated SOA particles was similar. For comparable OH exposures, α-pinene SOA yields were similar in the PAM and Caltech chambers, but m-xylene SOA yields were much lower in the PAM compared to the Caltech chamber.

Correction to “Relationship between aerosol oxidation level and hygroscopic properties of laboratory generated secondary organic aerosol (SOA) particles”

Correction to “Relationship between aerosol oxidation level and hygroscopic properties of laboratory generated secondary organic aerosol (SOA) particles”

Evaporation kinetics and phase of laboratory and ambient secondary organic aerosol

Field measurements of secondary organic aerosol (SOA) find significantly higher mass loads than predicted by models, sparking intense effort focused on finding additional SOA sources but leaving the fundamental assumptions used by models unchallenged. Current air-quality models use absorptive partitioning theory assuming SOA particles are liquid droplets, forming instantaneous reversible equilibrium with gas phase. Further, they ignore the effects of adsorption of spectator organic species during SOA formation on SOA properties and fate. Using accurate and highly sensitive experimental approach for studying evaporation kinetics of size-selected single SOA particles, we characterized room-temperature evaporation kinetics of laboratory-generated α-pinene SOA and ambient atmospheric SOA. We found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models. Adsorption of "spectator" organic vapors during SOA formation, and aging of these coated SOA particles, dramatically reduced the evaporation rate, and in some cases nearly stopped it. Ambient SOA was found to exhibit evaporation behavior very similar to that of laboratory-generated coated and aged SOA. For all cases studied in this work, SOA evaporation behavior is nearly size-independent and does not follow the evaporation kinetics of liquid droplets, in sharp contrast with model assumptions. The findings about SOA phase, evaporation rates, and the importance of spectator gases and aging all indicate that there is need to reformulate the way SOA formation and evaporation are treated by models.

INDOOR AIR QUALITY: Scented Products Emit a Bouquet of VOCs

A survey of selected scented consumer goods showed the products emitted more than 100 volatile organic compounds (VOCs), including some that are classified as toxic or hazardous by federal laws.1 Even products advertised as “green,” “natural,” or “organic” emitted as many hazardous chemicals as standard ones. Anne Steinemann, a professor of civil and environmental engineering and public affairs at the University of Washington, Seattle, and colleagues used gas chromatography–mass spectrometry to analyze VOCs given off by the products. They tested 25 air fresheners, laundry detergents, fabric softeners, dryer sheets, disinfectants, dish detergents, all-purpose cleaners, soaps, hand sanitizers, lotions, deodorants, and shampoos. Many of the products tested are top sellers in their category. A single fragrance in a product can contain a mixture of hundreds of chemicals, some of which (e.g., limonene, a citrus scent) react with ozone in ambient air to form dangerous secondary pollutants, including formaldehyde.2 The researchers detected 133 different VOCs. Most commonly detected were limonene, α- and β-pinene (pine scents), and ethanol and acetone (often used as carriers for fragrance chemicals).1 Steinemann and colleagues found the average number of VOCs emitted was 17.1 Each product emitted 1–8 toxic or hazardous chemicals, and close to half (44%) generated at least 1 of 24 carcinogenic hazardous air pollutants, such as acetaldehyde, 1,4-dioxane, formaldehyde, or methylene chloride.1 These hazardous air pollutants have no safe exposure level, according to the U.S. Environmental Protection Agency.3 Of the 133 VOCs detected, only ethanol was listed on any label (for 2 products), and only ethanol and 2-butoxyethanol were listed on any Material Safety Data Sheet (for 5 products and 1 product, respectively).1 The Consumer Product Safety Commission, which regulates cleaning supplies, air fresheners, and laundry products, currently does not require manufacturers to disclose any ingredients on the label, including fragrances in these products.4 The same is true for fragrances in personal care items, which are overseen by the Food and Drug Administration.5 The Household Product Labeling Act, currently under review in the U.S. Senate, would require manufacturers to label consumer products with all ingredients, including fragrance mixtures.6 “Disclosing all ingredients could be a first step to understanding potential toxicity and health effects,” says Steinemann. Although the authors did not seek to assess whether use of any of the products studied would be associated with any risk,1 Steinemann says she receives hundreds of letters, phone calls, and e-mails from people who report a variety of respiratory, dermatological, and neurological problems they attribute to scented products: “Children have seizures after exposure to dryer sheets, and adults pass out around air fresheners,” she says.7 Steinemann and colleague Stanley M. Caress have written elsewhere that 19% of respondents across two U.S. telephone surveys reported health problems they attributed to air fresheners, and nearly 11% reported irritation they attributed to scented laundry products vented outdoors.8 “It’s important to take people’s complaints seriously,” says Steinemann, because “these human experiences are helping to inform science.” One of her next projects will focus on biomarkers of exposure and effect to better understand how fragranced products may cause a range of adverse health effects. “The ultimate goal is to improve public health,” Steinemann says. For now, she recommends cleaning with basic supplies like vinegar and baking soda. Steinemann’s study “strongly suggests that we need to find unscented alternatives for cleaning our homes, laundry, and ourselves,” says Claudia Miller, an allergist and immunologist at the University of Texas Health Science Center at San Antonio. An expert in chemical sensitivity, or toxicant-induced loss of tolerance, Miller created the Quick Environmental Exposure and Sensitivity Inventory,9 a screening tool for chemical intolerance. According to Miller, products intended to keep homes smelling fresh can set people up for a lifetime of chemically induced illness, and repeated exposure to small amounts of household chemicals can trigger symptoms to previously tolerated chemicals.10 “The best smell is no smell,” Miller says.