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Atmospheric aerosol particles of primary or secondary, biogenic or anthropogenic origin are highly complex samples of changing composition in time and space. To assess their effects on climate or human health, the size-dependent chemical composition of these ubiquitous atmospheric constituents must be known. The development of novel analytical methods has enabled more detailed characterization of the organic composition of aerosols. This review gives an overview of the methods used in the chemical characterization of atmospheric aerosol particles, with a focus on mass-spectrometry techniques for organic compounds, either alone or in combination with chromatographic separation. Off-line, on-site, and on-line methods are covered, and the advantages and limitations of the different methods are discussed. The main emphasis is on methods used for detailed characterization of the composition of the organic compounds in aerosol particles. We address and summarize the current state of analytical methods used in aerosol research and discuss the importance of developing novel sampling strategies and analytical instrumentation. Graphical Abstract Challenges in the atmospheric aerosol analytics.

Rationale: On-line chemical characterization methods of atmospheric aerosols are essential to increase our understanding of physicochemical processes in the atmosphere, and to study biosphere-atmosphere interactions. Several techniques, including aerosol mass spectrometry, are nowadays available, but they all suffer from some disadvantages. In this research, desorption atmospheric pressure photoionization high-resolution (Orbitrap) mass spectrometry (DAPPI-HRMS) is introduced as a complementary technique for the fast analysis of aerosol chemical composition without the need for sample preparation., Methods: Atmospheric aerosols from city air were collected on a filter, desorbed in a DAPPI source with a hot stream of toluene and nitrogen, and ionized using a vacuum ultraviolet lamp at atmospheric pressure. To study the applicability of the technique for ambient aerosol analysis, several samples were collected onto filters and analyzed, with the focus being on selected organic acids. To compare the DAPPI-HRMS data with results obtained by an established method, each filter sample was divided into two equal parts, and the second half of the filter was extracted and analyzed by liquid chromatography/mass spectrometry (LC/MS)., Results: The DAPPI results agreed with the measured aerosol particle number. In addition to the targeted acids, the LC/MS and DAPPI-HRMS methods were found to detect different compounds, thus providing complementary information about the aerosol samples., Conclusions: DAPPI-HRMS showed several important oxidation products of terpenes, and numerous compounds were tentatively identified. Thanks to the soft ionization, high mass resolution, fast analysis, simplicity and on-line applicability, the proposed methodology has high potential in the field of atmospheric research., (Copyright © 2015 John Wiley & Sons, Ltd.)

A complete methodology based on LC-anisole-toluene dopant-assisted atmospheric pressure photoionization-IT-MS was developed for the determination of aldehydes in atmospheric aerosol particles. For the derivatization, ultrasound was used to accelerate the reaction between the target analytes and 2,4-dinitrophenylhydrazine. The developed methodology was validated for three different samples, gas phase, ultrafine (Dp = 30 ± 4 nm; where Dp stands for particle diameter) and all-sized particles, collected on Teflon filters. The method quantitation limits ranged from 5 to 227 pg. The accuracy and the potential matrix effects were evaluated using standard addition methodology. Recoveries ranged between 91.7 and 109.9%, and the repeatability and the reproducibility of the method developed between 0.5 and 8.0% and between 2.9 and 11.1%, respectively. The results obtained by the developed methodology compared to those provided by the previously validated method revealed no statistical differences. The method developed was applied to the determination of aldehydes in 16 atmospheric aerosol samples (30 nm and all-sized samples) collected at the Station for Measuring Forest Ecosystem-Atmosphere Relations II during spring 2011. The mean concentrations of aldehydes, and oxidation products of terpenes were between 0.05 and 82.70 ng/m(3)., (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Comprehensive two dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOF-MS) was used for screening and semiquantitation of semivolatile organic compounds in aerosol particles. As the volatility was a prerequisite parameter for the analysis, some compounds were transformed via derivatization such as silylation into more volatile ones. The identification of the analytes was made by comparing the GC retention indices and the TOF mass spectra with the NIST and the Golm metabolome database reference libraries. The data treatment was simplified by exploiting an additional classification of the identified compounds, namely the main functional group or specific element present in the molecule leading to different groups of compounds. This methodology was applied to identify compounds in 30 ± 4 nm, 50 ± 5 nm and total suspended particles (TSP) collected during spring and autumn of 2009 and summer of 2010 at the Station for Measuring Forest Ecosystem Atmosphere Relations (SMEAR II) at Hyytiälä (Finland). The number of identified compounds was higher than 400, which were the most relevant compounds present in the samples, in terms of concentrations. The analysis of aerosol particles of different sizes, collected simultaneously, revealed that the number of compounds increased with the particle size whereas the normalized response factor decreased in most of the cases, aldehydes being an exception. This decrease could be associated with the formation or aggregation of new compounds onto the particles when they grow in the atmosphere.

In this research, the two most common filter media, quartz and Teflon, were tested to obtain information about the possible adsorption of gas-phase compounds onto filters during long sample collection of atmospheric aerosols. Particles of nanometer-size for off-line chemical characterization were collected using a recently introduced differential mobility analyzer for size separation. Samples were collected at an urban site (Helsinki, SMEARIII station) during spring 2010. Sampling time was 4 to 10 days for particles 50, 40, or 30 nm in diameter. Sample air flow was 4 L/min. The sampling setup was arranged so that two samples were obtained for each sampling period almost simultaneously: one containing particles and adsorbed gas-phase compounds and one containing adsorbed gas-phase compounds only. Filters were extracted and analyzed for the presence of selected carboxylic acids, polyols, nitrogen-containing compounds, and aldehydes. The results showed that, in quartz filter samples, gas-phase adsorption may be responsible for as much as 100% of some compound masses. Whether quartz or Teflon, simultaneous collection of gas-phase zero samples is essential during the whole sampling period. The dependence of the adsorption of gas-phase compounds on vapor pressure and the effect of adsorption on the deposited aerosol layer are discussed.

In the present study, sample collection and preparation were directly integrated with a chromatographic system by coupling a particle-into-liquid sampler for the first time on-line with solid-phase extraction-liquid chromatography-tandem mass spectrometry. Several organic acids, such as adipic, hydroxyglutaric, mandelic, vanillic, cis-pinonic, pinic, azelaic and sebacic, were used in the research. For sample pretreatment and concentration, strong anion exchange material was used in the extraction. Sampling, extraction and analysis conditions were optimized to obtain reliable information about aerosol chemical composition. To evaluate the performance of the on-line coupled system, half of each sample was analysed on-line and the other half was derivatized and analysed off-line by gas chromatography-mass spectrometry. Comparison of the two techniques with use of t-test showed the results to be in an excellent agreement. Limits of detection of studied acids in on-line system were between 0.1 and 0.9 ng. The on-line coupled system is fast and reliable and a promising tool for the real time analysis of organic acids in atmospheric aerosols., (2010 Elsevier B.V. All rights reserved.)

Abstract: Twenty one organic compounds including three monocarboxylic and ten dicarboxylic acids, four aldehydes, three polyols and one amine were determined in 61 atmospheric aerosol particle samples with different sizes (30 ± 4-nm, 40 ± 5-nm, 50 ± 5-nm and total suspended particles) collected at two sampling sites, the SMEAR II and SMEAR III stations during different seasons of the year. Non supervised pattern recognition techniques, such as hierarchical cluster analysis and principal component analysis were used to study the influence of the collection place, the season of the year and the particle size on the concentration and behavior of the target compounds. The reliability of these results was proved using a supervised pattern recognition technique such as soft independent modeling of class analogy. The results achieved demonstrate that the chemical composition of the atmospheric aerosol particles is affected by the potential emission sources and the reactivity of the studied compounds under certain atmospheric conditions. In addition, from quantitative analysis methodologies partial least squares regression and principal component regression models were successfully used to clarify the influence of the number of nucleation events on the chemical composition of the particles. [Copyright &y& Elsevier]

Abstract: Atmospheric aerosol particles, collected with the particle-into-liquid sampler at SMEARII station in Finland in mid-August 2007, were analysed for biogenic acids. The sample pretreatment method, comprising solid-phase extraction with anion exchange and hydrophilic–lipophilic balance materials, was optimized. Extraction efficiencies of solid-phase extraction from 10 and 20ml samples were about 100%, with average relative standard deviation of 8.9%, in concentration range from 12.5 to 50ng/ml of the acid. Extraction of aldehydes was less successful, with efficiencies from 69 to 163% and average 10% deviation. Pretreated samples were analysed by reversed phase high performance liquid chromatography with ion trap mass spectrometric detection. Limits of detection achieved for organic acids with the analytical procedure developed ranged from 9 to 27μg/l of extracted sample, while limits of quantitation were from 31 to 90μg/l. Oxidation with ozone was used for the preparation of the acid of β-caryophyllene (β-caryophyllinic acid), which was also studied in aerosol samples. MS2 experiments were used to confirm the identification of trans-pinic, trans-pinonic and β-caryophyllinic acids. Azelaic, hexadecanoic, cis-pinonic, and cis- and trans-pinic acids were quantitated in the samples with use of authentic standards, while the concentrations of trans-pinonic and β-caryophyllinic acids were determined with cis-pinonic acid as surrogate. Also, the contribution of β-caryophyllene oxidation products to aerosol organic carbon was evaluated. Aldehydes could not be analysed in real samples due to the insufficient extraction. The particle-into-liquid sampler proved to be suitable for the collection of aerosol particles for the elucidation of daily and diurnal variation of selected species. The optimized sample pretreatment, together with the analysis method, offer a promising approach for the study of aerosol chemical composition, where artifact formation is minimal and time resolution is good. [Copyright &y& Elsevier]

Oxidation of β-caryophyllene with ozone followed by reduction was carried out in dichloromethane. Reaction led to the formation of β-caryophyllene aldehyde (11%, purity 90.8%) and β-nocaryophyllone aldehyde (79%, purity 99%). Compounds were purified and separated by liquid–liquid extraction and flash chromatography. Identifications were achieved by electron-impact and electrospray ionization mass spectrometry, and precise structures were confirmed by one and two-dimensional nuclear magnetic resonance spectroscopy. The prepared compounds were used in the analysis of ambient aerosol samples collected during spring 2003 at Hyytiälä, Finland. β-Nocaryophyllone aldehyde was positively identified and quantified in ambient aerosol samples for the first time. The amount of quantified β-nocaryophyllone aldehyde of aerosol origin was 17.4 ± 1.0 ng m−3 of sampled air. Comparison with previous findings led to the conclusion that oxidation products of β-caryophyllene participate in biogenic aerosol formation over boreal forest during late spring. [ABSTRACT FROM AUTHOR]

Measurements to clarify the chemical composition and especially the nitrogen compounds in 10nm ultrafine aerosol particles were carried out at the boreal forest site at the SMEAR II station, Hyytiälä, Finland, during spring–summer–autumn of 2010 and in spring 2011. In 2011, laser aerosol mass spectrometer (laser AMS) provided in-situ chemical composition data for 10nm particles. Laser AMS results, for samples collected in 2011, were clarified through comparison with findings for partly published 30nm and all-sized particles from filter samples analyzed by chromatographic techniques, re-analysis of the selected 30nm filter samples for quinoline identification by LC–MS and modified results from previously published atmospheric pressure interface time-of-flight mass spectrometer (APi-TOFMS) data. The chemistry of the atmosphere was found to change markedly in mid April 2011, just after snow melt: the concentrations of 35% of the laser AMS ions and compounds determined in 30nm particles from filter samples clearly increased or decreased at this time. Notably, the amount of nitrogen compounds increased and the amount of aldehydes decreased. The laser AMS results for 10nm aerosol samples demonstrated the tendency for nitrogen-containing compounds and oxygenated and non-oxygenated hydrocarbons to increase in concentration after snow melt. More detailed analysis confirmed that the two most interesting, frequently observed, and abundant laser AMS ions, m/z 143 and 185, originated from 1-(X-methylquinolin-X-yl) ethanone. According to laser AMS and APi-TOFMS data, when the quinoline concentrations in the 10nm particulate phase increased, the concentrations in the molecular clusters decreased, indicating changes in the partitioning between particle and gas phases. [ABSTRACT FROM AUTHOR]

Abstract: Organic compounds in atmospheric nanoparticles have an effect on human health and the climate. The determination of these particles is challenged by the difficulty of sampling, the complexity of sample composition, and the trace-level concentrations of the compounds. Meeting the challenge requires the development of sophisticated sampling systems for size-resolved particles and the optimization of sensitive, accurate and simple analytical techniques and methods. A new sampling system is proposed where particles are charged with a bipolar charger and size-segregated with a differential mobility analyzer. This system was successfully used to sample particles from wood pyrolysis with particle sizes 30–100nm. Particles were analyzed by four techniques: comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry, gas chromatography–time-of-flight mass spectrometry, gas chromatography–quadrupole mass spectrometry, and aerosol mass spectrometry (aerosol MS). In the chromatographic techniques, particles were collected on a filter and analyzed off-line after sample preparation, whereas in the aerosol MS, particle analysis was performed directly from the particle source. Target compounds of the samples were polyaromatic hydrocarbons and n-alkanes. The analytical techniques were compared and their advantages and disadvantages were evaluated. The sampling system operated well and target compounds were identified in low concentrations. [Copyright &y& Elsevier]

Abstract: The aim of this study was to characterize the organic composition of ambient ultrafine particles (<50nm) in a boreal forest environment and compare the analytical results obtained by different techniques with use a data analysis software. In the chromatographic techniques, particles were collected on a filter and analyzed off-line after sample preparation, whereas in the aerosol MS, particle analysis was performed directly from the particle source. Many compounds and chemical groups were identified with a laser aerosol mass spectrometer (laser AMS) and selected organic compounds, including acids, polyols, amines and aldehydes, from 50nm filter samples were quantified. Interesting components found with the laser AMS included oxygenated and aliphatic hydrocarbons, aromatic compounds, amines, and black carbon. The amines found on laser AMS may be related to new particle formation events at particle sizes 10–25nm. Correlations between the results obtained with different instruments were clarified, and the best correlations were found between laser AMS and 50-nm size filter samples. There were no correlations between the laser AMS data and meteorological data or on-line measured gas phase compounds. The black carbon found on laser AMS had moderate correlation for levoglucosan found on all-sized filter samples. Finally, the correlation analysis revealed that the information obtained from sub-50-nm size range particles and results for particles several times higher could not be directly compared. [Copyright &y& Elsevier]