Emily A. Bruns

Nonequilibrium atmospheric secondary organic aerosol formation and growth

Airborne particles play critical roles in air quality, health effects, visibility, and climate. Secondary organic aerosols (SOA) formed from oxidation of organic gases such as α-pinene account for a significant portion of total airborne particle mass. Current atmospheric models typically incorporate the assumption that SOA mass is a liquid into which semivolatile organic compounds undergo instantaneous equilibrium partitioning to grow the particles into the size range important for light scattering and cloud condensation nuclei activity. We report studies of particles from the oxidation of α-pinene by ozone and NO3 radicals at room temperature. SOA is primarily formed from low-volatility ozonolysis products, with a small contribution from higher volatility organic nitrates from the NO3 reaction. Contrary to expectations, the particulate nitrate concentration is not consistent with equilibrium partitioning between the gas phase and a liquid particle. Rather the fraction of organic nitrates in the particles is only explained by irreversible, kinetically determined uptake of the nitrates on existing particles, with an uptake coefficient that is 1.6% of that for the ozonolysis products. If the nonequilibrium particle formation and growth observed in this atmospherically important system is a general phenomenon in the atmosphere, aerosol models may need to be reformulated. The reformulation of aerosol models could impact the predicted evolution of SOA in the atmosphere both outdoors and indoors, its role in heterogeneous chemistry, its projected impacts on air quality, visibility, and climate, and hence the development of reliable control strategies.

Comparison of FTIR and Particle Mass Spectrometry for the Measurement of Particulate Organic Nitrates

While multifunctional organic nitrates are formed during the atmospheric oxidation of volatile organic compounds, relatively little is known about their signatures in particle mass spectrometers. High resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) and FTIR spectroscopy on particles impacted on ZnSe windows were applied to NH(4)NO(3), NaNO(3), and isosorbide 5-mononitrate (IMN) particles, and to secondary organic aerosol (SOA) from NO(3) radical reactions at 22 degrees C and 1 atm in air with alpha- and beta-pinene, 3-carene, limonene, and isoprene. For comparison, single particle laser ablation mass spectra (SPLAT II) were also obtained for IMN and SOA from the alpha-pinene reaction. The mass spectra of all particles exhibit significant intensity at m/z 30, and for the SOA, weak peaks corresponding to various organic fragments containing nitrogen [C(x)H(y)N(z)O(a)](+) were identified using HR-ToF-AMS. The NO(+)/NO(2)(+) ratios from HR-ToF-AMS were 10-15 for IMN and the SOA from the alpha- and beta-pinene, 3-carene, and limonene reactions, approximately 5 for the isoprene reaction, 2.4 for NH(4)NO(3) and 80 for NaNO(3). The N/H ratios from HR-ToF-AMS for the SOA were smaller by a factor of 2 to 4 than the -ONO(2)/C-H ratios measured using FTIR. FTIR has the advantage that it provides identification and quantification of functional groups. The NO(+)/NO(2)(+) ratio from HR-ToF-AMS can indicate organic nitrates if they are present at more than 15-60% of the inorganic nitrate, depending on whether the latter is NH(4)NO(3) or NaNO(3). However, unique identification of specific organic nitrates is not possible with either method.

Identification of significant precursor gases of secondary organic aerosols from residential wood combustion.

Organic gases undergoing conversion to form secondary organic aerosol (SOA) during atmospheric aging are largely unidentified, particularly in regions influenced by anthropogenic emissions. SOA dominates the atmospheric organic aerosol burden and this knowledge gap contributes to uncertainties in aerosol effects on climate and human health. Here we characterize primary and aged emissions from residential wood combustion using high resolution mass spectrometry to identify SOA precursors. We determine that SOA precursors traditionally included in models account for only ~3–27% of the observed SOA, whereas for the first time we explain ~84–116% of the SOA by inclusion of non-traditional precursors. Although hundreds of organic gases are emitted during wood combustion, SOA is dominated by the aging products of only 22 compounds. In some cases, oxidation products of phenol, naphthalene and benzene alone comprise up to ~80% of the observed SOA. Identifying the main precursors responsible for SOA formation enables improved model parameterizations and SOA mitigation strategies in regions impacted by residential wood combustion, more productive targets for ambient monitoring programs and future laboratories studies, and links between direct emissions and SOA impacts on climate and health in these regions.

Identification of Organic Nitrates in the NO3 Radical Initiated Oxidation of α-Pinene by Atmospheric Pressure Chemical Ionization Mass Spectrometry

The gas-phase reactions of nitrate radicals (NO3) with biogenic organic compounds are a major sink for these organics during night-time. These reactions form secondary organic aerosols, including organic nitrates that can undergo long-range transport, releasing NOx downwind. We report here studies of the reaction of NO3 with alpha-pinene at 1 atm in dry synthetic air (relative humidity approximately 3%) and at 298 K using atmospheric pressure chemical ionization triple quadrupole mass spectrometry (APCI-MS) to identify gaseous and particulate products. The emphasis is on the identification of individual organic nitrates in the particle phase that were obtained by passing the product mixture through a denuder to remove gas-phase reactants and products prior to entering the source region of the mass spectrometer. Filter extracts were also analyzed by GC-MS and by APCI time-of-flight mass spectrometry (APCI-ToF-MS) with methanol as the proton source. In addition to pinonaldehyde and pinonic acid, five organic nitrates were identified in the particles as well as in the gas phase: 3-oxopinane-2-nitrate, 2-hydroxypinane-3-nitrate, pinonaldehyde-PAN, norpinonaldehyde-PAN, and (3-acetyl-2,2-dimethyl-3-nitrooxycyclobutyl)acetaldehyde. Furthermore, there was an additional first-generation organic nitrate product tentatively identified as a carbonyl hydroxynitrate with a molecular mass of 229. These studies suggest that a variety of organic nitrates would partition between the gas phase and particles in the atmosphere, and serve as a reservoir for NOx.

Atmospheric solids analysis probe mass spectrometry: a new approach for airborne particle analysis.

Secondary organic aerosols (SOA) formed in the atmosphere from the condensation of semivolatile oxidation products are a significant component of airborne particles which have deleterious effects on health, visibility, and climate. In this study, atmospheric solids analysis probe mass spectrometry (ASAP-MS) is applied for the first time to the identification of organics in particles from laboratory systems as well as from ambient air. SOA were generated in the laboratory from the ozonolysis of alpha-pinene and isoprene, as well as from NO(3) oxidation of alpha-pinene, and ambient air was sampled at forested and suburban sites. Particles were collected by impaction on ZnSe disks, analyzed by Fourier transform-infrared spectroscopy (FT-IR) and then transferred to an ASAP-MS probe for further analysis. ASAP-MS data for the laboratory-generated samples show peaks from well-known products of these reactions, and higher molecular weight oligomers are present in both laboratory and ambient samples. Oligomeric products are shown to be present in the NO(3) reaction products for the first time. A major advantage of this technique is that minimal sample preparation is required, and complementary information from nondestructive techniques such as FT-IR can be obtained on the same samples. In addition, a dedicated instrument is not required for particle analysis. This work establishes that ASAP-MS will be useful for identification of organic components of SOA in a variety of field and laboratory studies.

Characterization of Gas-Phase Organics Using Proton Transfer Reaction Time-of-Flight Mass Spectrometry: Cooking Emissions.

Cooking processes produce gaseous and particle emissions that are potentially deleterious to human health. Using a highly controlled experimental setup involving a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS), we investigate the emission factors and the detailed chemical composition of gas phase emissions from a broad variety of cooking styles and techniques. A total of 95 experiments were conducted to characterize nonmethane organic gas (NMOG) emissions from boiling, charbroiling, shallow frying, and deep frying of various vegetables and meats, as well as emissions from vegetable oils heated to different temperatures. Emissions from boiling vegetables are dominated by methanol. Significant amounts of dimethyl sulfide are emitted from cruciferous vegetables. Emissions from shallow frying, deep frying and charbroiling are dominated by aldehydes of differing relative composition depending on the oil used. We show that the emission factors of some aldehydes are particularly large which may result in considerable negative impacts on human health in indoor environments. The suitability of some of the aldehydes as tracers for the identification of cooking emissions in ambient air is discussed.

Measurement of vapor pressures and heats of sublimation of dicarboxylic acids using atmospheric solids analysis probe mass spectrometry.

Vapor pressures of low volatility compounds are important parameters in several atmospheric processes, including the formation of new particles and the partitioning of compounds between the gas phase and particles. Understanding these processes is critical for elucidating the impacts of aerosols on climate, visibility, and human health. Dicarboxylic acids are an important class of compounds in the atmosphere for which reported vapor pressures often vary by more than an order of magnitude. In this study, atmospheric solids analysis probe mass spectrometry (ASAP-MS), a relatively new atmospheric pressure ionization technique, is applied for the first time to the measurement of vapor pressures and heats of sublimation of a series of dicarboxylic acids. Pyrene was also studied because its vapor pressures and heat of sublimation are relatively well-known. The heats of sublimation measured using ASAP-MS were in good agreement with published values. The vapor pressures, assuming an evaporation coefficient of unity, were typically within a factor of ∼3 lower than published values made at similar temperatures for most of the acids. The underestimation may be due to diffusional constraints resulting from evaporation at atmospheric pressure. However, this study establishes that ASAP-MS is a promising new technique for such measurements.

A New Aerosol Flow System for Photochemical and Thermal Studies of Tropospheric Aerosols

For studying the formation and photochemical/thermal reactions of aerosols relevant to the troposphere, a unique, high-volume, slow-flow, stainless steel aerosol flow system equipped with UV lamps has been constructed and characterized experimentally. The total flow system length is 8.5 m and includes a 1.2 m section used for mixing, a 6.1 m reaction section and a 1.2 m transition cone at the end. The 45.7 cm diameter results in a smaller surface to volume ratio than is found in many other flow systems and thus reduces the potential contribution from wall reactions. The latter are also reduced by frequent cleaning of the flow tube walls which is made feasible by the ease of disassembly. The flow tube is equipped with ultraviolet lamps for photolysis. This flow system allows continuous sampling under stable conditions, thus increasing the amount of sample available for analysis and permitting a wide variety of analytical techniques to be applied simultaneously. The residence time is of the order of an hour, and sampling ports located along the length of the flow tube allow for time-resolved measurements of aerosol and gas-phase products. The system was characterized using both an “inert” gas (CO 2 ) and particles (atomized NaNO 3 ). Instruments interfaced directly to this flow system include a NO x analyzer, an ozone analyzer, relative humidity and temperature probes, a scanning mobility particle sizer spectrometer, an aerodynamic particle sizer spectrometer, a gas chromatograph-mass spectrometer, an integrating nephelometer, and a Fourier transform infrared spectrophotometer equipped with a long path (64 m) cell. Particles collected with impactors and filters at the various sampling ports can be analyzed subsequently by a variety of techniques. Formation of secondary organic aerosol from α-pinene reactions (NO x photooxidation and ozonolysis) are used to demonstrate the capabilities of this new system.

The filter loading effect by ambient aerosols in filter absorption photometers depends on the mixing state of the sampled particles

[1] Research and Development Department, Aerosol d.o.o., Ljubljana, Slovenia [2] Condensed Matter Physics Department, Jožef Stefan Institute, Ljubljana, Slovenia 10 [3] Center for Atmospheric Research, University of Nova Gorica, Nova Gorica, Slovenia [4] Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland [5] Institut National de l’Environnement Industriel et des Risques, Verneuil-en-Halatte, France [6 ]Laboratoire des Sciences du Climat et de l’Environnement (CNRS-CEA-UVSQ), CEA Orme des Merisiers, Gif-sur-Yvette, France 15 [7] Energy Environment and Water Research Center,The Cyprus Institute, Nicosia, Cyprus [8] Desert Research Institute, Nevada System of Higher Education, Reno, USA [9] MTA-SZTE Research Group on Photoacoustic Spectroscopy, Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary [#] now at: Lucerne University of Applied Sciences and Arts, School of Engineering and Architecture, 20 Bioenergy Research, Horw, Switzerland [

Development, characterization and first deployment of an improved online reactive oxygen species analyzer

] now at: Air Lorraine, Metz, France [+] now at: Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, MO, USA [%] now at: College of Optical Sciences, University of Arizona, Tucson, AZ, USA 25