Aerosol Chemistry Resolved by Mass Spectrometry: Insights into

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Aerosol Chemistry Resolved by Mass Spectrometry: Insights into Particle Growth after Ambient New Particle Formation Alexander L. Vogel,*,†,§ Johannes Schneider,‡ Christina Müller-Tautges,† Thomas Klimach,‡ and Thorsten Hoffmann*,† †

Institute for Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany Particle Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany

‡

S Supporting Information *

ABSTRACT: Atmospheric oxidation of volatile organic compounds (VOCs) yields a large number of different organic molecules which comprise a wide range of volatility. Depending on their volatility, they can be involved in new particle formation and particle growth, thus affecting the number concentration of cloud condensation nuclei in the atmosphere. Here, we identified oxidation products of VOCs in the particle phase during a field study at a rural mountaintop station in central Germany. We used atmospheric pressure chemical ionization mass spectrometry ((−)APCI-MS) and aerosol mass spectrometry for time-resolved measurements of organic species and of the total organic aerosol (OA) mass in the size range of 0.02−2.5 and 0.05−0.6 μm, respectively. The elemental composition of organic molecules was determined by offline analysis of colocated PM 2.5 filter samples using liquid chromatography coupled to electrospray ionization ultrahigh-resolution mass spectrometry. We found extremely low volatile organic compounds, likely from sesquiterpene oxidation, being the predominant signals in the (−)APCI-MS mass spectrum during new particle formation. Low volatile organic compounds started to dominate the spectrum when the newly formed particles were growing to larger diameters. Furthermore, the APCI-MS mass spectra pattern indicated that the average molecular weight of the OA fraction ranged between 270 and 340 amu, being inversely related to OA mass. Our observations can help further the understanding of which biogenic precursors and which chemical processes drive particle growth after atmospheric new-particle formation.

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(ELVOCs).11−13 Experiments at a simulation chamber showed that gas-phase ELVOCs are sufficiently functionalized and their mixing ratios (at atmospherically relevant precursor concentrations) are large enough for the nucleation of molecular clusters, even without sulfuric acid being involved.14 Typical saturation mass concentration of molecules that nucleate falls into the ELVOC regime with C* < 10−4.5 μg/m3, while LVOCs are necessary to explain observed growth rates of particles >5 nm.15 In particular, the dimers observed from α-pinene ozonolysis are effectively nonvolatile and therefore potentially important for new particle formation and growth.16 However, evidence that these dimers play a role in ambient new particle formation needs to be provided while only a few field studies have described α-pinene derived dimers in ambient particlephase samples.17,18 Furthermore, it remains poorly elucidated whether it is condensation of gas-phase oxidation products,

INTRODUCTION A major source of uncertainty in global climate models is caused by aerosol particle number concentration related effects on cloud properties.1 New particle formation can be a dominant source of cloud condensation nuclei (CCN) if condensable vapors grow small clusters fast enough to prevent coagulational scavenging and large enough that the particles can be activated into cloud droplets.2−4 Understanding of nucleation and growth of ambient aerosol particles requires knowledge about the involved molecules, their sources or formation pathways, and their physicochemical properties. Although it has been shown that sulfuric acid is an essential gas involved in ambient new particle formation, it cannot explain observed ambient nucleation rates alone.5 Other trace gases, such as ammonia and amines, are suspected to promote atmospheric nucleation.6,7 Oxidation products of volatile organic compounds (VOCs) were already considered over a decade ago as potential candidates involved in atmospheric new particle formation.8−10 Recent studies have identified highly oxidized multifunctional compounds (HOMs) in the gas phase, of which a fraction is considered as extremely low volatility organic compounds © XXXX American Chemical Society

Received: April 5, 2016 Revised: August 23, 2016 Accepted: September 16, 2016

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DOI: 10.1021/acs.est.6b01673 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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Environmental Science & Technology

process, can still result in fragmentation of thermo-labile molecules. Different to the earlier described setup, in this work the HEPA-filter/valve setup between the concentrator and the APCI-MS was replaced by a charcoal denuder to remove gaseous species (see Figure S2). Blank values were measured daily by manually inserting a particle filter in front of the concentrator. The mean signal height on each mass-to-charge ratio (m/z) during the blank filter intervals were linearly interpolated and subtracted from the measured signal. Mass spectra were acquired between m/z 80 and m/z 500, and 200 microscans were averaged into one recorded spectrum resulting in a measurement frequency of approximately one mass spectrum per minute. Offline UHPLC/(−)ESI-UHRMS/Nontarget Analysis. PTFE-coated quartz fiber filters (Pallflex T60A20, Pall Life Science, U.S.) were used for sampling the excess PM 2.5 inlet air flow (∼27.5 LPM) between 6 and 30 h throughout the campaign (Figure S2). The filters were stored in glass vials at −18 °C until analysis. A field blank sample was collected by placing a filter in the filter holder at the field site for approximately half an hour without sample flow. Depending on the sampled volume, one-quarter or a half of the filter was cut into small pieces and extracted with 1.5 mL methanol (HPLC grade) using a vortex shaker for 30 min. The extraction step was repeated twice with 1 mL of methanol, and the combined extracts were evaporated to dryness under a gentle stream of nitrogen at 30 °C. The residue was dissolved in 10% methanolic solution and directly measured by liquid chromatography−mass spectrometry (LC-MS) to avoid esterification reactions. The measurements were carried out using an UHPLC system (Dionex UltiMate 3000, Thermo Scientific) with a Hypersil Gold column (C18, 50 × 2.0 mm, 1.9 μm particle size, Thermo Scientific). During the measurements the auto sampler temperature was set to 20 °C, and the column compartment temperature was 25 °C. Eluent A (ultrapure water with 2% acetonitrile and 0.04% formic acid) and B (acetonitrile with 2% ultrapure water) were used in gradient mode with a flow rate of 500 μL/min. The optimized gradient was 1% B at 0 min, 1% B at 1 min, 20% B at 2 min, 20% B at 5 min, 30% B at 6 min, 50% B at 7 min, 99% B at 7.5 min, and 99% B at 8 min. The injection volume was 10 μL per run, and each filter extract was measured in triplicate. High-resolution mass spectra were obtained using a QExactive mass spectrometer (Thermo Scientific, U.S.) equipped with a heated electrospray ionization (HESI) ion source at 120 °C. The HESI source was operated in negative ion mode with 60 psi sheath gas, 20 psi auxiliary gas (both nitrogen), 320 °C capillary temperature, and −3.3 kV spray voltage. The fullMS mode was used with a scan range of m/z 80−500 and a resolving power of R = 70 000 at m/z 200. Mass calibration was carried out using the Pierce ESI Negative Calibration Solution with additional 4-hydroxybutanoic-acid to calibrate for masses smaller than 250 amu. The resulting data were analyzed by the nontarget screening approach using a commercially available software (SIEVE, Thermo Scientific). A signal intensity threshold value of 1 × 105 counts in the three-dimensional space of retention time 0.7−7 min vs m/z 80−500 versus signal intensity was applied for all filter samples. The software automatically searches for signals above the threshold value which are significantly different from the blank chromatogram. Further-

reactive uptake and salt formation, or oligomerization of small organics that drives ambient particle growth.19 Real-time measurements of particle-phase composition in the relevant size range between 5 and 100 nm are very rare. Especially the organic fraction, which dominates this size regime, requires new soft ionization techniques to produce molecular ions for mass spectrometric detection. Recent online techniques that try to address organic speciation of the organic fraction are either designed for size-resolved20,21 or bulk aerosol measurements.22−26 Other size-resolved mass spectrometric techniques, such as the nano aerosol mass spectrometer (NAMS), can provide additional information on the elemental composition of nanoparticles and derive an oxygen-to-carbon ratio of the carbonaceous fraction.27,28 The objective of this work was to characterize the ambient organic aerosol fraction at a rural mountaintop station in central Germany using state-of-the-art mass spectrometry techniques. We used two complementary online aerosol mass spectrometers: the AMS for quantitative measurements of the aerosol inorganic and organic fraction and a chemical ionization mass spectrometer operating at atmospheric pressure ((−)APCI-MS) for measuring organic aerosol species which are ionized in the negative mode. Furthermore, offline analysis of filter samples using ultrahigh-performance liquid chromatography coupled to electrospray ionization ultrahigh-resolution mass spectrometry (UHPLC/(−)ESI-UHRMS) was used as a complementary technique to the online (−)APCI-MS to determine the elemental composition of the organic molecules. A companion paper, describing results from the same field campaign, addresses how soft ionization techniques allow the linking of the chemical composition of secondary organic aerosol (SOA) to their CCN activity.29

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EXPERIMENTAL SECTION Field Site Description. Measurements were conducted during the INUIT-TO campaign at the rural mountaintop research station at Mt. Kleiner Feldberg, located in central Germany (Taunus Observatorium, 826 m a.s.l., operated by the Goethe-University/Frankfurt) in August 2012. The surrounding area is dominated by Norway spruce; the large-scale area to the northwest is dominated by mixed forests and agricultural lands. To the northwest, the area is sparsely populated, whereas in the south to southeast the heavily populated Rhine-Main area with the cities Frankfurt, Wiesbaden, and Mainz lies within a distance of approximately 30 km. All instruments were arranged closely with the inlets at the same altitude and at a distance of 30 nm; thus, we emphasize that the mass spectra are not representative of the chemical composition of freshly nucleated particles below 20 nm. The 30 min average mass spectrum in the early morning represents the composition of a residual particle size mode. The second average mass spectrum from 12:00 to 12:30 h indicates that the concentration of the organic compounds as well as sulfuric acid (m/z 97) increased compared to the early morning spectrum. When new particles are forming, the strongest signals appear on odd masses in the range between 250 and 350 amu. Comparison between the noon and the evening spectrum shows the most pronounced

Figure 3. (A) FMPS number-size distribution (5 min average). (B) FMPS mass-size distribution (density = 1.5 g/cm3) and measurement ranges of the APCI-MS and AMS. The signal above the white lines in the FMPS distributions is caused by instrumental counting noise. (C) Average 30 min APCI-MS mass spectra during three different time intervals on the August 16, 2012. The early morning average spectrum comprises the chemical composition of residual particles. The noon average spectrum (dark green) during the ongoing nucleation event shows highest relative intensities in the 250−350 amu size range. The evening spectrum (light green) indicates a strong increase of compounds in the 150−250 amu size range. The signal at m/z 97 originates from sulfate.

changes of characteristics of the mass spectrum. Between those two average periods, particles have grown considerably to larger sizes and the base peak of the mass spectrum has shifted from m/z 299 to m/z 203. The evening mass spectrum shows a clear bimodal distribution which cannot be observed in the average noon mass spectrum during the nucleation event. D


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well-resolved isomers can be observed. Although the intensities are very low, the peaks show a low standard deviation and are significantly different from the field blank samples. According to the accurate mass measurement, the elemental composition of the compounds at m/z 299.1502 can be determined with high certainty to be C15H24O6. Zhao et al. postulate a structure to this elemental composition based on laboratory-generated secondary organic aerosol from α-cedrene.38 Because the LCMS analysis was conducted in the negative ESI-mode, this compound likely contains a carboxylic acid functional group. If we assume that the remaining oxygen atoms are due to two hydroxyl- and two keto-functional groups (similar to the hydrated ß-oxocaryophyllonic acid), the SIMPOL.1 model predicts an equilibrium vapor pressure of 1.7 × 10−13 Torr (at 293 K). The saturation vapor pressure of the molecule at m/ z 299 postulated by Zhao et al. can be estimated to be 1.8 × 10−14 Torr (at 293 K). The two other chromatograms of nominal mass m/z 313 and 345 do not reveal proper signals in the LC-MS analysis, although these signals are prominent in the online APCI-MS spectrum. However, we observe a broad enhancement in the exact mass traces of m/z 313.1295 and m/z 345.1192 compared to the blank samples. As it has been described by Kourtchev et al.,40 poor chromatographic resolution might smear compounds on the column, which can result in broad peaks and bad detection limits. However, the exact masses of those two compounds refer to the elemental composition of C15H22O7 and C15H22O9, respectively. Increasing number of oxygen is associated with a further reduction of the saturation vapor pressure and the presence of additional functional groups. Although we cannot provide direct evidence, the overall high abundance of C15-compounds during the nucleation event suggests an important role of sesquiterpene oxidation products in the initial formation and growth of molecular clusters. Low saturation vapor pressures and sufficient hydrogen bonding sites are key for the formation of stable molecular clusters. It has been shown that higher volatile and less functionalized compounds than sesquiterpene oxidation products can already form stable molecular clusters together with sulfuric acid or other ELVOCs and that it is the number of hydrogen bonding sites which correlates with the stability of molecular cluster.41 Therefore, ambient studies in different environments and chamber studies on nucleation rates from sesquiterpene oxidation are needed to better understand their role in new particle formation. Linking SOA Composition to Particle Growth. Immediately after the new particle formation event on August 16, 2012 we observed particle growth up to sizes at which they can act as CCN. Figure 5 depicts a parametrization of the FMPS measurements on August 16, 2012 into four different lognormal size distribution modes. Starting conditions and boundaries as well as an animation of the parametrization are provided in the Supporting Information. The integrated particle number concentration of mode 1 (Dp ∼ 10 nm) and 2 (Dp ∼ 20 nm) peaks around noon, when new particles are formed most efficiently (Figure 5B). At 15:00 h, the number concentration of these two size modes appear back at the levels observed before the event. Particles at 10 nm are likely affected by a low-voltage drift in the FMPS, which results in the counting of smaller particles at this size channel. This artifact might explain the strong band of particles observed at 10 nm. During the event, the number concentration of mode 3 increased by almost 1 order of magnitude and remains at higher

Elemental composition of the unit mass resolution online (−)APCI-MS signals has been achieved by complementary offline UHPLC/(−)ESI-UHRMS analysis of filter samples. The nontarget screening approach resulted in a peak list of molecules with identified elemental composition (see Table S1). If a molecule on a certain unit mass has been verified by the offline measurement, it is indicated by colored circles on top of the APCI-MS spectrum in Figure 4. This analysis

Figure 4. Average (−)APCI-MS mass spectrum during August 16, 2012 18:00−19:00 h. Circles represent identified molecules by the offline UHPLC/(−)ESI-UHRMS nontarget analysis, classified into the composition groups CHO, CHNOS, CHOS, and CHNO (see Table S1). The colored bar is an estimate of the volatility classes.

indicates that each major signal in the APCI-MS spectrum has been verified by offline analysis. Hence, ion source cluster formation is not distorting the online (−)APCI-MS mass spectrum. Furthermore, it can be seen that molecules which contain only carbon, hydrogen, and oxygen dominate the mass spectrum at that certain time period. Offline UHPLC/(−)ESI-UHRMS analysis of a filter, which was sampled during the NPF event, enabled us to identify two isobaric interferences at the APCI-MS base peak (m/z 299) as C14H20O7 and C15H24O6. Exemplary LC-UHRMS chromatograms of UMR masses at m/z 283, 299, 313, and 345 are shown in Figure S3. The chromatogram of the accurate mass at m/ z 283.1555 can be attributed to the elemental composition of C15H24O5 (Figure S3A). It shows the abundance of five isomers which seem to be partly lipophilic because of the relatively long retention time on the reversed phase column. An oxidation product of the sesquiterpene ß-caryophyllene on this accurate mass has been described by Chan et al.,37 namely hydrated ßoxocaryophyllonic acid. More recently, a study by Zhao et al.38 describes the identification of several oxidation products from α-cedrene in a chamber experiment. Molecules with the same elemental composition were observed during the ambient nucleation event. Furthermore, the abundance of five isomers resolved by LC-MS suggests that different sesquiterpene precursors form similar oxidation products. The estimation of the saturation vapor pressure of the hydrated ß-oxocaryophyllonic acid by applying the SIMPOL.139 model results in 3.9 × 10−12 Torr (at 293 K). Although this molecule is not as highly oxidized as ELVOCs described by Ehn et al., it falls into the ELVOC regime because of the organic acid functionality and the larger number of carbon atoms. The extracted ion chromatogram (EIC) of m/z 299.1502 is shown in Figure S3B. Three distinct and chromatographically E


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Figure 5. Parametrized FMPS size distribution using four log-normal size distributions. (A) Particle growth can be observed most clearly in mode 3 starting from 28 nm at 15:00 h to 40 nm at 19:00 h. (B) Mode 1 and 2 peak during the early new particle formation, while mode 3 and 4 increase later during the event.

Figure 6. (A) AMS chemical composition during the new particle formation event and subsequent particle growth on August 16, 2012. (B) Particle growth being linked to the evolution of two organic mass traces of the APCI-MS. The MBTCA signal (m/z 203) is rising while the mean diameter of mode 3 increases. (C) The appearance of mode 4 is linked to the appearance of sulfuric acid. While mode 3 starts growing from 15:00 h onward, sulfuric acid remains constant, indicating that sulfuric acid is not contributing to the particle growth.

values, although new particle formation has slowed during the later hours of the day. It is likely that mode 3 is continuously supplied with particles which are growing out of the size modes 1 and 2. Particle growth is shown in Figure 5A as the progression of the mean diameter of the four different modes. It can be seen that mode 1 remains constant throughout the whole day, while the diameter of mode 2 starts increasing in the early afternoon. Shortly afterward, the fitted mode diameter decreases because it grew out of the allowed fitting boundaries. From 15:00 h onward, mode 3 shows clear particle growth throughout the whole afternoon and early night, starting at Dp = 27 nm at 15:00 h to Dp = 41 nm at 24:00 h. The average growth rate from 15:00 h until 18:00 h is 2.9 ± 1.8 nm/h. We observe that organic aerosol mass from AMS measurements and particle-phase organic acid signals in the 150−250 amu region in the APCI-MS spectrum increase during the observed particle growth of mode 3 (Figure 6A+B). The depicted APCI-MS mass traces m/z 203 and m/z 299 are exemplary molecules representing the S-/LVOC and L-/ ELVOC regions, respectively. A higher signal intensity of m/z 299 can be observed during the peak of the new particle formation event (11:00 h−13:00 h). Both signals rise during the afternoon; however, when particle size mode 3 starts growing at around 15:00 h, the signal at m/z 203 continues increasing while m/z 299 stays constant for the rest of the day. The increase of this signal is not affected by larger accumulation mode particles, as the mass of these particles slightly decreases during the afternoon. We interpret this observation as a contribution to particle growth by LVOCs formed in the gas phase from more volatile precursor molecules.42 The exemplary case of this process is the gas-phase MBTCA production from cis-pinonic acid under OH oxidation.35 We note that a part of

the increase in LVOC signal can also originate from particlephase transformation (aging) which is not necessarily affecting the mass-size distribution measured by the FMPS. While different organic molecules correlate with growing particles of size mode 3 (Figure 6B), the organic aerosol measured by AMS shows already at 13:00 h a steeper increase of OA (Figure 6A). This is likely caused by hydrocarbon-like OA that is not detected by APCI-MS. The trend of the sulfuric acid signal (m/z 97) (Figure 6A,C) shows that particle growth is not driven by sulfuric acid condensation. Because the sulfuric acid signal is strongly linked to the sudden increase of particles in the largest size mode (mode 4), it seems likely that these particles rather originate from a distant pollution source. Molecular Weight of SOA. The appearance of the mode at 150−250 amu between the noon and evening average mass spectra (Figure 3 C) can be explained by the partitioning theory,43 which implies that a species of a certain volatility partitions with increasing particle mass to a greater extent into the particle phase. Volatility of organic molecules is, beside their functionalities, also affected by their molecular weight.44 Thus, it explains that the compounds of the smaller m/z mode are less present in the particle phase during nucleation because of their semivolatile character. However, those compounds appear to be important for the growth of particles to larger sizes. The increased partitioning of smaller molecules with higher particle mass appears in Figure 7 as a decrease of the average molecular weight with increasing particle mass. We observe that the F


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A.L.V.: Laboratory for Environmental Chemistry & Laboratory for Atmospheric Chemistry, Paul Scherrer Institute, Villigen 5232, Switzerland. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Max Planck Graduate Center together with the Johannes Gutenberg-Universität Mainz (MPGC). The INUIT-TO 2012 field campaign was initiated by the DFG-funded research unit INUIT (FOR 1525). We thank H. Bingemer and University of Frankfurt technicial staff for field site support, F. Drewnick for providing the MoLa, and T. Böttger and S.-L. von der Weiden-Reinmüller for support during the setup of the aerosol inlets and the MoLa.

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Figure 7. Intensity weighted average molecular weight versus mass concentration of the particle-phase organic composition. OA is organic aerosol mass determined by the AMS, and PM1 is total aerosol mass determined by the EDM 180.

(1) Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change: Summary for Policymakers; IPCC, Ed.; Cambridge University Press: Cambridge, United Kingdom, 2013. (2) Kulmala, M.; Kontkanen, J.; Junninen, H.; Lehtipalo, K.; Manninen, H. E.; Nieminen, T.; Petaja, T.; Sipila, M.; Schobesberger, S.; Rantala, P.; Franchin, A.; Jokinen, T.; Jarvinen, E.; Aijala, M.; Kangasluoma, J.; Hakala, J.; Aalto, P. P.; Paasonen, P.; Mikkila, J.; Vanhanen, J.; Aalto, J.; Hakola, H.; Makkonen, U.; Ruuskanen, T.; Mauldin, R. L., III; Duplissy, J.; Vehkamaki, H.; Back, J.; Kortelainen, A.; Riipinen, I.; Kurten, T.; Johnston, M. V.; Smith, J. N.; Ehn, M.; Mentel, T. F.; Lehtinen, K. E. J.; Laaksonen, A.; Kerminen, V.-M.; Worsnop, D. R. Direct Observations of Atmospheric Aerosol Nucleation. Science 2013, 339 (6122), 943−946. (3) Vehkamaki, H.; Riipinen, I. Thermodynamics and kinetics of atmospheric aerosol particle formation and growth. Chem. Soc. Rev. 2012, 41 (15), 5160−5173. (4) Dusek, U.; Frank, G. P.; Hildebrandt, L.; Curtius, J.; Schneider, J.; Walter, S.; Chand, D.; Drewnick, F.; Hings, S.; Jung, D.; Borrmann, S.; Andreae, M. O. Size matters more than chemistry for cloud-nucleating ability of aerosol particles. Science 2006, 312 (5778), 1375−1378. (5) Kerminen, V.-M.; Petaja, T.; Manninen, H. E.; Paasonen, P.; Nieminen, T.; Sipila, M.; Junninen, H.; Ehn, M.; Gagne, S.; Laakso, L.; Riipinen, I.; Vehkamaki, H.; Kurten, T.; Ortega, I. K.; Dal Maso, M.; Brus, D.; Hyvarinen, A.; Lihavainen, H.; Leppa, J.; Lehtinen, K. E. J.; Mirme, A.; Mirme, S.; Horrak, U.; Berndt, T.; Stratmann, F.; Birmili, W.; Wiedensohler, A.; Metzger, A.; Dommen, J.; Baltensperger, U.; Kiendler-Scharr, A.; Mentel, T. F.; Wildt, J.; Winkler, P. M.; Wagner, P. E.; Petzold, A.; Minikin, A.; Plass-Duelmer, C.; Poeschl, U.; Laaksonen, A.; Kulmala, M. Atmospheric nucleation: highlights of the EUCAARI project and future directions. Atmos. Chem. Phys. 2010, 10 (22), 10829−10848. (6) Kirkby, J.; Curtius, J.; Almeida, J.; Dunne, E.; Duplissy, J.; Ehrhart, S.; Franchin, A.; Gagne, S.; Ickes, L.; Kuerten, A.; Kupc, A.; Metzger, A.; Riccobono, F.; Rondo, L.; Schobesberger, S.; Tsagkogeorgas, G.; Wimmer, D.; Amorim, A.; Bianchi, F.; Breitenlechner, M.; David, A.; Dommen, J.; Downard, A.; Ehn, M.; Flagan, R. C.; Haider, S.; Hansel, A.; Hauser, D.; Jud, W.; Junninen, H.; Kreissl, F.; Kvashin, A.; Laaksonen, A.; Lehtipalo, K.; Lima, J.; Lovejoy, E. R.; Makhmutov, V.; Mathot, S.; Mikkila, J.; Minginette, P.; Mogo, S.; Nieminen, T.; Onnela, A.; Pereira, P.; Petaja, T.; Schnitzhofer, R.; Seinfeld, J. H.; Sipila, M.; Stozhkov, Y.; Stratmann, F.; Tome, A.; Vanhanen, J.; Viisanen, Y.; Vrtala, A.; Wagner, P. E.; Walther, H.; Weingartner, E.; Wex, H.; Winkler, P. M.; Carslaw, K. S.; Worsnop, D. R.; Baltensperger, U.; Kulmala, M. Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature 2011, 476 (7361), 429−U77. (7) Almeida, J.; Schobesberger, S.; Kuerten, A.; Ortega, I. K.; Kupiainen-Maatta, O.; Praplan, A. P.; Adamov, A.; Amorim, A.;

average molecular weight of the organic aerosol fraction can be found as high as 340 g/mol when the particle mass is below 1 μg/m3 and as low as 270 g/mol for higher particle mass. Our findings demonstrate that particle growth to CCN sizes at regions influenced by biogenic VOC emissions can substantially be driven by condensation of semi- and lowvolatile organic species which are likely formed by gas-phase oxidation processes. The majority of the condensing organic species are molecules which consist of only carbon, hydrogen, and oxygen. Organonitrates, organosulfates, and nitrooxyorganosulfates have been observed during this study as well, but not during the investigated nucleation event day. The identification of several highly abundant C15-compounds is an indication for sesquiterpene emissions at this field site, which has been investigated by other studies.45,46 Sesquiterpene oxidation products generally fall into the ELVOC regime and can thus be considered as potentially important molecules for the initial cluster formation during new particle formation events.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.6b01673. Figures related to the text (e.g., chromatograms of the LC-UHRMS analysis), the boundaries for the FMPS parametrization, an FMPS parametrization example figure, a table containing the results of the nontarget analysis, and a number−size distribution plot of the aerodynamic particle sizer (PDF) Animation of the FMPS parametrization (AVI)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*Paul Scherrer Institut, 5232 Villigen, Switzerland; phone: +41 56 310 4395; e-mail: [email protected]. *Duesbergweg 10-14, Johannes Gutenberg-Universität, 55128 Mainz; phone: +49 6131 39 25716; e-mail: t.hoff[email protected]. G


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Aerosol Chemistry Resolved by Mass Spectrometry: Insights into

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