Annular diffusion denuder for simultaneous removal of gaseous organic compounds and air oxidants during sampling of carbonaceous aerosols

Particle-phase accretion forms dimer esters in pinene secondary organic aerosol

Secondary organic aerosol (SOA) is ubiquitous in the atmosphere and plays a pivotal role in climate, air quality, and health. The production of low-volatility dimeric compounds through accretion reactions is a key aspect of SOA formation. However, despite extensive study, the structures and thus the formation mechanisms of dimers in SOA remain largely uncharacterized. In this work, we elucidate the structures of several major dimer esters in SOA from ozonolysis of α-pinene and β-pinene-substantial global SOA sources-through independent synthesis of authentic standards. We show that these dimer esters are formed in the particle phase and propose a mechanism of nucleophilic addition of alcohols to a cyclic acylperoxyhemiacetal. This chemistry likely represents a general pathway to dimeric compounds in ambient SOA.

Simultaneous Determination of Gaseous Ammonia and Particulate Ammonium in Ambient Air Using a Cylindrical Wet Effluent Diffusion Denuder and a Continuous Aerosol Sampler

A sensitive and fast method for simultaneous determination of gaseous ammonia (NH₃) and particulate ammonium (NH₄⁺) in ambient air is presented. NH₃ is sampled in a cylindrical wet effluent diffusion denuder (CWEDD) and analyzed online by a continuous flow system with a fluorescence detector (FLD), while NH₄⁺ bound to aerosol particles is sampled in parallel by a condensation growth unit-the aerosol counterflow two-jet unit (CGU-ACTJU) sampler-and analyzed online with another FLD. The sensitive fluorescence detection of ammonium in concentrates of the CWEDD and the ACTJU is based on its reaction with ortho-phthaldialdehyde and sulfite to form isoindol-1-sulfonate. The calibration curve of ammonium is linear in the concentration range of 5 × 10^-9 to 2 × 10^-6 M. The limit of detection (LOD = 3 s/n) values of NH₃ and NH₄⁺ are 3.52 ng m^-3 (5.05 ppt) and 1.04 ng m^-3, respectively. The developed method enables online measuring of distribution of NH₃/NH₄⁺ in ambient air with a time resolution of 1 s. The optimized method was used for the determination of NH₃/NH₄⁺ in urban air in Brno in two campaigns during the winter and summer of 2018. The results obtained by the developed method were compared with a reference method based on the sampling on filters and "dry" diffusion denuders coated by phosphoric acid.

Characterization and Source Identification of Elements and Water-Soluble Ions in Submicrometre Aerosols in Brno and Šlapanice (Czech Republic)

Submicrometre aerosol particles (particulate matter, PM1) were collected in two Czech cities (Brno and Šlapanice) during week campaigns in winter and summer of 2009 and 2010. The aerosols were analysed for 14 elements and 12 water-soluble ions using inductively coupled plasma–mass spectrometry and ion chromatography techniques. The average PM1 mass concentration was 14.4 and 20.4 µg m−3 in Brno and Šlapanice, respectively. Most of the analysed elements and ions exhibit distinct seasonal variability with higher concentrations in winter in comparison to summer. The determined elements and ions together accounted for about 29% of total PM1 mass, ranging between 16% and 44%. Ion species were the most abundant components in collected aerosols, accounting for 27.2% of mass of PM1 aerosols, and elements accounted for 1.8% of mass of PM1 aerosols. One-day backward trajectories were calculated using the Hysplit model to analyse air masses transported towards the sampling sites. The Pearson correlation coefficients between individual PM1 components and PM1 mass and air temperature were calculated. To identify the main aerosol sources, factor analysis was applied. Six factors were identified for each locality. The following sources of PM1 particles were identified in Brno: a municipal incinerator, vehicle exhausts, secondary sulphate, a cement factory, industry and biomass burning. The identified sources in Šlapanice were as follows: a combustion source, coal combustion, a cement factory, a municipal incinerator, vehicle exhausts and industry.

Determination of short-term changes in levoglucosan and dehydroabietic acid in aerosols with Condensation Growth Unit - Aerosol Counterflow Two-Jets Unit - LC-MS

Residential areas in urban agglomerations and also in the countryside are often burdened with high concentrations of aerosol in winter, this originating from local combustion sources. Aerosol sources can be identified by a monitoring of organic markers of biomass burning. Abundant markers of biomass and softwood burning are levoglucosan and dehydroabietic acid, respectively. The aim of this research was to develop an analytical method for the determination of levoglucosan and dehydroabietic acid in aerosol over short time periods involving aerosol sampling into liquid samples, quantitative pre-concentration of analytes, and their determination by liquid chromatography - mass spectrometry. A Condensation Growth Unit - Aerosol Counterflow Two-Jets Unit (CGU-ACTJU) sampler was used for the quantitative collection of aerosol directly into water. Dehydroabietic acid was pre-concentrated from the aqueous phase by solid phase extraction (C-18). Afterwards, levoglucosan in water samples was concentrated on a vacuum evaporator. The detection limits of levoglucosan and dehydroabietic acid were 28 ng m^-3 and 5.5 ng m^-3, respectively. The results obtained by the developed method were compared with an independent determination of both markers in aerosol by means of the sampling of aerosols on a filter and subsequent analysis by GC-MS. The developed method demonstrated sufficient agreement with the independent determination for generated standard aerosol as well as for urban aerosol over an eight-day winter campaign. The presented method allows the monitoring of concentration changes in biomass burning markers in 2-h intervals.

Aerosol sampler for analysis of fine and ultrafine aerosols

A new aerosol sampler based on the original version of Aerosol Counterflow Two-Jets Unit (ACTJU) is described. The ACTJU collector, connected with a water-based Condensation Growth Unit (CGU) placed upstream of the ACTJU, accomplished the quantitative collection of fine and ultrafine aerosol particles down to a few nanometers in diameter. Condensation of water vapor in the CGU enlarges nanometer sized particles to larger sizes in the supermicrometer range and the formed droplets are then collected into water in the ACTJU collector. The continuous collection of aerosols with the CGU-ACTJU sampler allows for the time-resolved measurement of changes in the concentration of particulate constituents. Coupling of the CGU-ACTJU sampler with on-line detection devices allows in-situ automated analysis of water-soluble aerosol components with high time resolution of 1 s (e.g., FIA detection for nitrite or nitrate) or 1 h (e.g., IC detection with preconcentration step for inorganic anions). Under the optimum conditions (the air flow rate of 10 L min^-1 and water flow rate of 1.5 mL min^-1), the limit of detection (IC including the preconcentration) for particulate fluoride, chloride, nitrite, nitrate, sulphate and phosphate is 2.53, 6.64, 24.2, 16.8, 0.12 and 5.03 ng m^-3, respectively. The apparatus is sufficiently robust for its application at routine monitoring of aerosol composition in real-time.

VUV photoionization aerosol mass spectrometric study on the iodine oxide particles formed from O3-initiated photooxidation of diiodomethane (CH2I2)

IOPs formed from O₃-initiated photooxidation of CH₂I₂ were investigated based on the combination of a thermal desorption/tunable vacuum ultraviolet time-of-flight photoionization aerosol mass spectrometer with a flow reactor for the first time.

Reactions of Atmospheric Particulate Stabilized Criegee Intermediates Lead to High-Molecular-Weight Aerosol Components

Aging of organic aerosol particles is one of the most poorly understood topics in atmospheric aerosol research. Here, we used an aerosol flow tube together with an iodide-adduct high-resolution time-of-flight chemical-ionization mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-HRToF-CIMS) to investigate heterogeneous ozonolysis of oleic acid (OL), developing a comprehensive oxidation mechanism with observed products. In addition to the well-known first-generation C9 products including nonanal, nonanoic acid, azelaic acid, and 9-oxononanoic acid, the iodide-adduct chemical ionization permitted unambiguous determination of a large number of high-molecular-weight particulate products up to 670 Da with minimum amounts of fragmentation. These high-molecular-weight products are characterized by a fairly uniform carbon oxidation state but stepwise addition of a carbon backbone moiety, and hence continuous decrease in the volatility. Our results demonstrate that heterogeneous oxidation of organic aerosols has a significant effect on the physiochemical properties of organic aerosols and that reactions of particulate SCIs from ozonolysis of an unsaturated particulate species represent a previously underappreciated mechanism that lead to formation of high-molecular-weight particulate products that are stable under typical atmospheric conditions.

Use of a versatile high efficiency multiparallel denuder for the sampling of PAHs in ambient air: gas and particle phase concentrations, particle size distribution and artifact formation

The design and performance of a multiparallel plate denuder able to operate at low and high-flow (3-30 L/min) for the collection of polycyclic aromatic hydrocarbon (PAH) vapor is described. The denuder, in combination with a micro orifice uniform deposit impactor (MOUDI) was used to assess processes of artifact formation in MOUDIs used with and without an upstream denuder. Duplicate sampling trains with an upstream denuder showed good repeatability of the measured gas and particle-phase concentrations and low breakthrough in the denuder (3.5-15%). The PAH size distributions within undenuded and denuded MOUDIs were studied. Use of the denuder altered the measured size distribution of PAHs toward smaller sizes, but both denuded and undenuded systems are subject to sampling artifacts.