Compounds In Aerosol Particles Research Articles

Enhancing characterization of organic nitrogen components in aerosols and droplets using high-resolution aerosol mass spectrometry

Abstract. This study aims to enhance the understanding and application of the Aerodyne high-resolution aerosol mass spectrometer (HR-AMS) for the comprehensive characterization of organic nitrogen (ON) compounds in aerosol particles and atmospheric droplets. To achieve this goal, we analyzed 75 N-containing organic compounds, representing a diverse range of ambient non-organonitrate ON (NOON) types, including amines, amides, amino acids, N heterocycles, protein, and humic acids. Our results show that NOON compounds can produce significant levels of NHx+ and NOx+ ion fragments, which are typically recognized as ions representative of inorganic nitrogen species. We also identified the presence of CH2N+ at m/z = 28.0187, an ion fragment rarely quantified in ambient datasets due to substantial interference from N2+. As a result, the utilization of an updated calibration factor of 0.79 is necessary for accurate NOON quantification via the HR-AMS. We also assessed the relative ionization efficiencies (RIEs) for various NOON species and found that the average RIE for NOON compounds (1.52 ± 0.58) aligns with the commonly used default value of 1.40 for organic aerosol. Moreover, through a careful examination of the HR-AMS mass spectral features of various NOON types, we propose fingerprint ion series that can aid the NOON speciation analysis. For instance, the presence of CnH2n+2N+ ions is closely linked with amines, with CH4N+ indicating primary amines, C2H6N+ suggesting secondary amines, and C3H8N+ representing tertiary amines. CnH2nNO+ ions (especially for n values of 1–4) are very likely derived from amides. The co-existence of three ions, C2H4NO2+, C2H3NO+, and CH4NO+, serves as an indicator for the presence of amino acids. Additionally, the presence of CxHyN2+ ions indicates the occurrence of 2N-heterocyclic compounds. Notably, an elevated abundance of NH4+ is a distinct signature for amines and amino acids, as inorganic ammonium salts produce only negligible amounts of NH4+ in the HR-AMS. Finally, we quantified the NOON contents in submicron particles (PM1) and fog water in Fresno, California, and PM1 in New York City (NYC). Our results revealed the substantial presence of amino compounds in both Fresno and NYC aerosols, whereas concurrently collected fog water in Fresno contained a broader range of NOON species, including N-containing aromatic heterocycle (e.g., imidazoles) and amides. These findings highlight the significant potential of employing the widespread HR-AMS measurements of ambient aerosols and droplets to enhance our understanding of the sources, transformation processes, and environmental impacts associated with NOON compounds in the atmosphere.

Chemical characterization of marine aerosols from two cruises over the South China Sea: Importance of biomass burning and secondary formation

Total suspended particle (TSP) samples were collected during June–July 2015 in the northern South China Sea (NSCS) and August–September 2016 in the western South China Sea (WSCS). Water-soluble ions (WSIs), organic carbon (OC), elemental carbon (EC), and organic compounds were measured. The average concentrations of WSIs, OC, EC and organic compounds were 19.4 ± 10.9 μg m−3, 2.48 ± 1.54 μgC m−3, 0.31 ± 0.25 μgC m−3 and 789 ± 217 ng m−3 in the NSCS, and were 10.2 ± 4.71 μg m−3, 1.76 ± 1.82 μgC m−3, 0.43 ± 0.32 μgC m−3 and 781 ± 342 ng m−3 in the WSCS. In both cruises, sea salt ions (Na+ and Cl−) and secondary inorganic ions (SO42−, NO3−, and NH4+) were the main species of WSIs, accounting for 54.0 % and 43.6 % in the NSCS, and for 35.0 % and 54.0 % in the WSCS. The secondary products (dicarboxylic acids and aromatic acids) (NSCS: 73.3 %; WSCS: 73.9 %) and saccharides (NSCS: 19.0 %; WSCS: 18.0 %) accounted large fractions of organic compounds in aerosol particles over the SCS. These results suggest sea salt emissions and secondary formation are the main sources of the aerosols over the SCS in summer. The positive correlations between the biomass burning tracers (nss-K+ and levoglucosan) and OC as well as organic compounds indicated that biomass burning from nearby continents was also an important source of organic aerosols over the SCS. Based on back-trajectory analysis and satellite fire spots, Indochina Peninsula and China were proposed as the main continental source areas of non-sea salt WSIs and organic compounds. Our results highlight the significant contribution of continental outflow especially biomass burning and photochemical secondary oxidation to the organic compositions of aerosol particles over the SCS in summertime.

Chemical properties of HULIS from three different environments

Humic-like substances (HULIS) comprise a significant fraction of the organic compounds in aerosol particles. In the present study we report the chemical properties of HULIS samples originating from urban (Copenhagen, Denmark), rural (Melpitz, Germany) and remote (Storm Peak Laboratory, CO, USA) environments. Suwannee River Fulvic Acid Standard (SRFA) was included in the study as a reference. Raman, Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy were used together with high performance liquid chromatography-mass spectrometry (HPLC-MS) for characterisation of the samples. The same main functional groups were present in all samples, but the relative abundance of functional groups varied among the studied samples, which was mainly evident from the FTIR spectra. The urban and rural samples were found to be very similar with respect to the relative abundance of functional groups. The remote sample contained relatively more C=O and COOH groups, which may be due to the remote environment. Organonitrates appeared to be present in the three atmospheric samples, while it did not appear to be present in the SRFA. The SRFA sample comprised significantly larger amounts of aromatic groups relative to the atmospheric samples in line with previous findings. All the obtained mass spectra showed clear periods of 14-16 Da in line with previous studies. The estimated average molecular weight (AMW) was comparable for the atmospheric samples within the errors - while the AMW of SRFA was higher. In general the atmospheric HULIS samples from different environments were rather similar with respect to the properties investigated.

Methods for characterization of organic compounds in atmospheric aerosol particles

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.

Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulations

Atmospheric amino acids constitute a large fraction of water-soluble organic nitrogen compounds in aerosol particles, and have been confirmed as effective cloud condensation nuclei (CCN) materials in laboratory experiments. We present a molecular dynamics (MD) study of six amino acids with different structures and chemical properties that are relevant to the remote marine atmospheric aerosol–cloud system, with the aim of investigating the detailed mechanism of their induced changes in surface activity and surface tension, which are important properties for cloud drop activation. Distributions and orientations of the amino acid molecules are studied; these l-amino acids are serine (SER), glycine (GLY), alanine (ALA), valine (VAL), methionine (MET) and phenylalanine (PHE) and are categorised as hydrophilic and amphiphilic according to their affinities to water. The results suggest that the presence of surface-concentrated amphiphilic amino acid molecules give rise to enhanced Lennard–Jones repulsion, which in turn results in decreased surface tension of a planar interface and an increased surface tension of the spherical interface of droplets with diameters below 10 nm. The observed surface tension perturbation for the different amino acids under study not only serves as benchmark for future studies of more complex systems, but also shows that amphiphilic amino acids are surface active. The MD simulations used in this study reproduce experimental results of surface tension measurements for planar interfaces and the method is therefore applicable for spherical interfaces of nano-size for which experimental measurements are not possible to conduct.

The effect of humidity on the ozonolysis of unsaturated compounds in aerosol particles

Atmospheric aerosol particles are important in many atmospheric processes such as: light scattering, light absorption, and cloud formation. Oxidation reactions continuously change the chemical composition of aerosol particles, especially the organic mass component, which is often the dominant fraction. These ageing processes are poorly understood but are known to significantly affect the cloud formation potential of aerosol particles. In this study we investigate the effect of humidity and ozone on the chemical composition of two model organic aerosol systems: oleic acid and arachidonic acid. These two acids are also compared to maleic acid an aerosol system we have previously studied using the same techniques. The role of relative humidity in the oxidation scheme of the three carboxylic acids is very compound specific. Relative humidity was observed to have a major influence on the oxidation scheme of maleic acid and arachidonic acid, whereas no dependence was observed for the oxidation of oleic acid. In both, maleic acid and arachidonic acid, an evaporation of volatile oxidation products could only be observed when the particle was exposed to high relative humidities. The particle phase has a strong effect on the particle processing and the effect of water on the oxidation processes. Oleic acid is liquid under all conditions at room temperature (dry or elevated humidity, pure or oxidized particle). Thus ozone can easily diffuse into the bulk of the particle irrespective of the oxidation conditions. In addition, water does not influence the oxidation reactions of oleic acid particles, which is partly explained by the structure of oxidation intermediates. The low water solubility of oleic acid and its ozonolysis products limits the effect of water. This is very different for maleic and arachidonic acid, which change their phase from liquid to solid upon oxidation or upon changes in humidity. In a solid particle the reactions of ozone and water with the organic particle are restricted to the particle surface and hence different regimes of reactivity are dictated by particle phase. The potential relevance of these three model systems to mimic ambient atmospheric processes is discussed.

Occurrence of Zinc and Lead in Aerosols and Deposits in the Fluidized-Bed Combustion of Recovered Waste Wood. Part 2: Thermodynamic Considerations

In the present work, which is the second part in a series of two, multi-phase, multi-component equilibrium calculations were used to study the chemistry and deposition behavior of lead and zinc in the combustion of recovered waste wood (RWW). Particular attention was paid to the deposition behavior in different parts of the boiler under varying flue gas and material temperature conditions. In addition, the influence of fuel composition was considered by studying three different fuel compositions. The results from the calculations were compared to experimental results from two measurement campaigns, whose goal was to experimentally determine the distribution and speciation of zinc and lead compounds in aerosol particles and deposits in the fluidized-bed combustion of RWW. The results from the experimental work are presented in part 1 (10.1021/ef101478n) of this work.

Occurrence of Zinc and Lead in Aerosols and Deposits in the Fluidized-Bed Combustion of Recovered Waste Wood. Part 1: Samples from Boilers

Combustion of recovered waste wood (RWW) has led to increased fouling and corrosion of furnace walls, superheaters, and economizers. These problems have been associated mainly with chlorine, zinc, and lead in the deposits but also with sodium and titanium. The presence of lead and zinc compounds, especially lead and zinc chlorides, has been shown to increase the corrosivity of the deposits even at relatively low metal temperatures (230−450 °C). The present work determined experimentally the distribution and speciation of zinc and lead compounds in aerosol particles and deposits in the fluidized-bed combustion of RWW. Measurements were conducted in both a full-scale (20 MWth) plant with as-received RWW and in a pilot-scale (2 MWth) setup with as-received RWW and RWW doped with zinc and lead. The results show that the amount and speciation of zinc and lead in the deposits vary depending upon the fuel composition, flue gas temperature, and metal temperature. Both lead and zinc chlorides are found in temperat...

Comprehensive two-dimensional gas chromatography, a valuable technique for screening and semiquantitation of different chemical compounds in ultrafine 30 nm and 50 nm aerosol particles

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.

A VUV photoionization organic aerosol mass spectrometric study with synchrotron radiation

A photoionization aerosol time-of-flight mass spectrometer (ATOFMS) has been developed for on-line analysis of organic compounds in aerosol particles using tunable vacuum ultraviolet (VUV) synchrotron radiation. Aerosol particles can be sampled directly from atmospheric pressure and are focused through an aerodynamic lens assembly into the mass spectrometer. The particles are vaporized when they impact on a heater, and then the nascent vapor is softly photoionized by synchrotron radiation. The degree of fragmentation of molecule can be controlled either by the heater temperature or by the photon energy. Thus, fragment-free tunable VUV mass spectra are obtained by tuning the photon energy close to the ionization energies (IEs) of the sample molecules. The direct determination of the IEs of benzophenone (9.07 eV), salicylic acid (8.72 eV), and urea (9.85 eV) are measured from the photoionization efficiency spectra with uncertainties of ±50 meV. Ab initio calculations have been employed to predict the theoretical ionization energy.

Characterization of organic compounds in aerosol particles from a coniferous forest by GC–MS

Atmospheric aerosol particles were collected in a Finnish Scots pine forest as part of a European Union project. Sampling was done in March–April 2003 with a high-volume sampler. Dynamic ultrasonic-assisted solvent extraction and gas chromatography–mass spectrometry (GC–MS) were applied to the analysis of aerosol samples for analytes such as n-alkanes, polycyclic aromatic hydrocarbons (PAH), oxidized polycyclic aromatic hydrocarbons (oxy-PAHs), sesquiterpenes (SQT) and oxidized sesquiterpenes (oxy-SQT). The highest concentrations were found for the n-alkanes, which were present in a wide range (C11–C32) indicating both biogenic and anthropogenic sources. PAH compounds were found in every sample while oxy-PAH compounds were present in low concentrations in a few samples. A few oxidized monoterpenes, most notably (−)-verbenone and pinonaldehyde, were found in several samples in concentrations clearly exceeding the PAH concentrations. The effect of temperature could be seen in most samples, where the concentrations of n-alkanes declined with decreasing temperatures. Particle formation events were accompanied by higher concentrations of heavy n-alkanes, verbenone and pinonaldehyde.

Characterisation of organic compounds in aerosol particles from a Finnish forest by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry.

During the European Union project Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST), which began in spring 2003, atmospheric aerosol particles were collected in a Finnish Scots pine forest using a high-volume sampler. The organic compounds in the filter samples were then analysed by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS). The sample was first extracted by SFE. During LC the extracts were fractionated into three fractions according to polarity. The final separation was carried out by GC-MS. A fraction volume as high as 840 microL was transferred to the GC, using the partial concurrent eluent evaporation technique. The same instrumentation, with an in-situ SFE derivatisation method, was used to analyse organic acids. Major compounds such as n-alkanes and PAH were analysed quantitatively. Their concentrations were lower than those usually observed in urban areas or in other forest areas in Europe. The wind direction was one of the most important factors affecting changes in the daily concentrations of these compounds. Scots pine needles were analysed with the same system to obtain reference data for identification of biogenic compounds in aerosol particles. Other organic compounds found in this study included hopanes, steranes, n-alkanals, n-alkan-2-ones, oxy-PAH, and alkyl-PAH; some biogenic products, including oxidation products of monoterpenes, were also identified.

Concentration trends and mixing states of particulate oxalate in Arctic boundary layer in winter/spring

Particulate organic species contribute to the formation of cloud condensation nuclei and may play a role in the formation/growth of condensation nuclei. The field measurements in this paper investigated size distribution and mixing states of particulate oxalate (one of major organic compounds in aerosol particles) in the Arctic boundary layer in during the winter and spring. The variation of particulate oxalate concentration correlated well with nss‐SO42− concentration. This correlation may be due to the direct emissions of oxalate and its precursors of oxalate from anthropogenic sources. The molar ratio of oxalate to nss‐SO42− was found to gradually increase from winter to early spring with the recovery of solar radiation to the Arctic Circle. Individual aerosol particle analysis by means of laser microprobe mass spectrometry showed that most of the oxalate was internally mixed with sulfate in fine particle mode (0.2–2.0 μm).

Coupling two-step laser desorption/ ionization with aerosol time-of-flight mass spectrometry for the analysis of individual organic particles

Analysis of organic compounds in aerosol particles using real-time single particle techniques is difficult because of extensive fragmentation that occurs in the laser desorption/ionization step. In an effort to avoid such fragmentation processes, we coupled a “soft” two-step laser desorption/ionization technique (L2MS) with aerosol time-of-flight mass spectrometry (ATOFMS). In these studies, we find this combination preserves intact organic molecules while providing the real-time mass spectra of suspended aerosol particles. Mass spectra of particles analyzed by one-step desorption mass spectrometry and L2MS are presented for comparison. These include 2,4-dihydroxybenzoic acid as a test case and wood and cigarette combustion particles as real world examples. This is the first published demonstration of L2MS performed on single particles not deposited on a substrate prior to analysis.

Principal component analysis of summertime organic aerosols at Niwot Ridge, Colorado

The organic constituents of atmospheric aerosols collected at Niwot Ridge, Colorado, along with various physical and meteorological data, were measured during a collaborative field study. Temporal changes in the composition of samples collected during summertime at Niwot Ridge, a rural site in the Rocky Mountains west of Denver, were studied. Volatile organic compounds were thermally desorbed from aerosol particles, separated by gas chromatography, and identified by mass spectrometry. For each of 48 2‐ to 5‐hour samples, 18 organic compounds in aerosol particles, 11 organic and inorganic compounds in the vapor phase, wind direction, and time of day were measured. Relationships among the variables were analyzed by principal component analysis in order to examine the covariations within the data set. The 31 variables are grouped into seven factors, and individual compounds, as well as the factors, serve as molecular markers for biologic and anthropogenic emission sources. Elucidation of several distinct associations within both rural and urban air masses was possible because of the high time resolution achieved in the collection and analysis of aerosols. In addition, factor scores were used to illustrate how several organic compounds vary with respect to local atmospheric dynamics.

Chromatographic measurement of molecular markers of sources of atmospheric aerosol particles

Various organic compounds in aerosol particles in ambient air near a coniferous forest fire in Boulder, Colorado were identified as molecular markers of wood burning and forest fires. Particle samples were collected by filtering small volumes of air. The samples were analysed using thermal desorption followed by gas chromatographic separation and detection, a highly sensitive analytical method. Several compounds unique to softwood combustion were identified in the samples. Additionally, a predominance of odd-carbon-numbered n-alkanes over the corresponding even-carbon-numbered n-alkanes was observed. This predominance is a well-documented molecular pattern indicative of epicutical waxes in plants.