Papers by R. Schnitzhofer
Scientific Reports, 2015
reported from the biosphere to the atmosphere. Here, using evidence from measurements at aircraft... more reported from the biosphere to the atmosphere. Here, using evidence from measurements at aircraft, ecosystem, tree, branch and leaf scales, with complementary isotopic labeling experiments, we show that vegetation (leaves, flowers, and phytoplankton) emits a wide variety of benzenoid compounds to the atmosphere at substantial rates. Controlled environment experiments show that plants are able to alter their metabolism to produce and release many benzenoids under stress conditions. The functions of these compounds remain unclear but may be related to chemical communication and protection against stress. We estimate the total global secondary organic aerosol potential from biogenic benzenoids to be similar to that from anthropogenic benzenoids (~10 Tg y −1 ), pointing to the importance of these natural emissions in atmospheric physics and chemistry.
Atmospheric Measurement Techniques Discussions, 2009
A method for real time profiling of volatile organic compounds (VOCs) was developed combining the... more A method for real time profiling of volatile organic compounds (VOCs) was developed combining the advantages of a tethered balloon as a research platform and of proton transfer reaction mass spectrometry (PTR-MS) as an analytical technique for fast and highly sensitive VOC measurements. A 200 m Teflon tube was used to draw sampling 5 air from a tethered aerodynamic balloon to the PTR-MS instrument. Potential positive and negative VOC artifacts of the inlet line were characterized in the laboratory and in the field and were found to be insignificant for most compounds. The method was successfully deployed during a winter field campaign to determine the small scale spatial and temporal pattern of air pollutants under winter inversion conditions. 10 flight altitude of ∼150 m above ground level (a.g.l.) over the continents. The lowest 1772 AMTD
Atmospheric Measurement Techniques, 2014
The CLOUD experiment (Cosmics Leaving OUtdoor Droplets) investigates the nucleation of new partic... more The CLOUD experiment (Cosmics Leaving OUtdoor Droplets) investigates the nucleation of new particles and how this process is influenced by galactic cosmic rays in an electropolished, stainless-steel environmental chamber at CERN (European Organization for Nuclear Research). Since volatile organic compounds (VOCs) can act as precursor gases for nucleation and growth of particles, great efforts have been made to keep their unwanted background levels as low as possible and to quantify them. In order to be able to measure a great set of VOCs simultaneously in the low parts per trillion (pptv) range, proton-transferreaction mass spectrometry (PTR-MS) was used. Initially the total VOC background concentration strongly correlated with ozone in the chamber and ranged from 0.1 to 7 parts per billion (ppbv). Plastic used as sealing material in the ozone generator was found to be a major VOC source. Especially oxygen-containing VOCs were generated together with ozone. These parts were replaced by stainless steel after CLOUD3, which strongly reduced the total VOC background. An additional ozone-induced VOC source is surfaceassisted reactions at the electropolished stainless steel walls. The change in relative humidity (RH) from very dry to humid conditions increases background VOCs released from the chamber walls. This effect is especially pronounced when the RH is increased for the first time in a campaign. Also the dead volume of inlet tubes for trace gases that were not continuously flushed was found to be a short but strong VOC contamination source. For lower ozone levels (below 100 ppbv) the total VOC contamination was usually below 1 ppbv and therewith considerably cleaner than a comparable Teflon chamber. On average about 75 % of the total VOCs come from only five exact masses (tentatively assigned as formaldehyde, acetaldehyde, acetone, formic acid, and acetic acid), which have a rather high vapour pressure and are therefore not important for nucleation and growth of particles.
Atmospheric Chemistry and Physics, 2015
The formation of particles from precursor vapors is an important source of atmospheric aerosol. R... more The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new-particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH 3 ) and sulfuric acid (H 2 SO 4 ). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH 3 -H 2 SO 4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH 3 ] in the range from < 2 to 1400 pptv, [H 2 SO 4 ] from 3.3 × 10 6 to 1.4 × 10 9 cm −3 (0.1 to 56 pptv), and a temperature range from −25 to +20 • C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF)
Atmospheric Chemistry and Physics Discussions, 2014
The Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H 2 O, Organics & Nitrogen (BE... more The Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H 2 O, Organics & Nitrogen (BEACHON) project seeks to understand the feedbacks and interrelationships between hydrology, biogenic emissions, carbon assimilation, aerosol properties, clouds and associated feedbacks within water-limited ecosystems. The
Plos One, 2011
Proton transfer reaction-time of flight (PTR-TOF) mass spectrometry was used to improve detection... more Proton transfer reaction-time of flight (PTR-TOF) mass spectrometry was used to improve detection of biogenic volatiles organic compounds (BVOCs) induced by leaf wounding and darkening. PTR-TOF measurements unambiguously captured the kinetic of the large emissions of green leaf volatiles (GLVs) and acetaldehyde after wounding and darkening. GLVs emission correlated with the extent of wounding, thus confirming to be an excellent indicator of mechanical damage. Transient emissions of methanol, C5 compounds and isoprene from plant species that do not emit isoprene constitutively were also detected after wounding. In the strong isoprene-emitter Populus alba, light-dependent isoprene emission was sustained and even enhanced for hours after photosynthesis inhibition due to leaf cutting. Thus isoprene emission can uncouple from photosynthesis and may occur even after cutting leaves or branches, e.g., by agricultural practices or because of abiotic and biotic stresses. This observation may have important implications for assessments of isoprene sources and budget in the atmosphere, and consequences for tropospheric chemistry. Citation: Brilli F, Ruuskanen TM, Schnitzhofer R, Mü ller M, Breitenlechner M, et al. (2011) Detection of Plant Volatiles after Leaf Wounding and Darkening by Proton Transfer Reaction ''Time-of-Flight'' Mass Spectrometry (PTR-TOF). PLoS ONE 6(5): e20419.
Meteorology and Atmospheric Physics, 2009
This study analyzes the structure of the wintertime boundary layer in an Alpine valley (Inn Valle... more This study analyzes the structure of the wintertime boundary layer in an Alpine valley (Inn Valley, Austria) for a case of high air pollution. We present airborne aerosol observations collected with particle counters and a backscatter lidar. The effect of upslope winds on the spatial distribution of pollutants is investigated. An asymmetry in the aerosol distribution is observed in the cross-valley direction which presumably is related to differences in orientation and albedo of the two valley slopes. A one-sided thermal circulation, which develops above the sun-exposed slope, is most likely responsible for the observed redistribution of aerosols during daytime. Elevated aerosol layers form at the height of shallow inversion layers. Despite this vertical transport of pollutants by slope winds, no effective vertical venting of the polluted air mass into the free atmosphere can be achieved.
Journal of Geophysical Research, 2011
1] Eddy covariance flux measurements were carried out for two subsequent vegetation periods above... more 1] Eddy covariance flux measurements were carried out for two subsequent vegetation periods above a temperate mountain grassland in an alpine valley using a proton-transfer-reaction-mass spectrometer (PTR-MS) and a PTR time-of-flight-mass spectrometer (PTR-TOF). In 2008 and during the first half of the vegetation period 2009 the volume mixing ratios (VMRs) for the sum of monoterpenes (MTs) were typically well below 1 ppbv and neither MT emission nor deposition was observed. After a hailstorm in July 2009 an order of magnitude higher amount of terpenes was transported to the site from nearby coniferous forests causing elevated VMRs. As a consequence, deposition fluxes of terpenes to the grassland, which continued over a time period of several weeks without significant reemission, were observed. For days without precipitation the deposition occurred at velocities close to the aerodynamic limit. In addition to monoterpene uptake, deposition fluxes of the sum of sesquiterpenes (SQTs) and the sum of oxygenated terpenes (OTs) were detected. Considering an entire growing season for the grassland (i.e., 1 April to 1 November 2009), the cumulative carbon deposition of monoterpenes reached 276 mg C m −2 . This is comparable to the net carbon emission of methanol (329 mg C m −2 ), which is the dominant nonmethane volatile organic compound (VOC) emitted from this site, during the same time period. It is suggested that deposition of monoterpenes to terrestrial ecosystems could play a more significant role in the reactive carbon budget than previously assumed.
Atmospheric Measurement Techniques, 2009
A method for real-time profiling of volatile organic compounds (VOCs) was developed combining the... more A method for real-time profiling of volatile organic compounds (VOCs) was developed combining the advantages of a tethered balloon as a research platform and of proton transfer reaction mass spectrometry (PTR-MS) as an analytical technique for fast and highly sensitive VOC measurements. A 200 m Teflon tube was used to draw sampling air from a tethered aerodynamic balloon to the PTR-MS instrument. Positive and negative artefacts (i.e. formation and loss of VOCs in the tube) were characterised in the laboratory and in the field by a set of 11 atmospherically relevant VOCs including both pure and oxygenated hydrocarbons. The only two compounds that increased or decreased when sampled through the tube were acetone (+7%) and xylene (−6%). The method was successfully deployed during a winter field campaign to determine the small scale spatial and temporal patterns of air pollutants under winter inversion conditions.
Atmospheric Measurement Techniques, 2010
The recently developed PTR-TOF instrument was evaluated to measure methanol fluxes emitted from g... more The recently developed PTR-TOF instrument was evaluated to measure methanol fluxes emitted from grass land using the eddy covariance method. The high time resolution of the PTR-TOF allowed storing full mass spectra up to m/z 315 with a frequency of 10 Hz. Three isobaric ions were found at a nominal mass of m/z 33 due to the high mass resolving power of the PTR-TOF. Only one of the three peaks contributed to eddy covariance fluxes. The exact mass of this peak agrees well with the exact mass of protonated methanol (m/z 33.0335). The eddy covariance methanol fluxes measured with PTR-TOF were compared to virtual disjunct eddy covariance methanol fluxes simultaneously measured with a conventional PTR-MS. The methanol fluxes from both instruments show excellent agreement.
Atmospheric Chemistry and Physics, 2009
In order to investigate the spatial distribution of air pollutants in the Inn valley (Tyrol, Aust... more In order to investigate the spatial distribution of air pollutants in the Inn valley (Tyrol, Austria) during wintertime, a joint field campaign of the three research projects
Atmospheric Chemistry and Physics, 2011
Eddy covariance (EC) is the preferable technique for flux measurements since it is the only direc... more Eddy covariance (EC) is the preferable technique for flux measurements since it is the only direct flux determination method. It requires a continuum of high time resolution measurements (e.g. 5-20 Hz). For volatile organic compounds (VOC) soft ionization via proton transfer reaction has proven to be a quantitative method for real time mass spectrometry; here we use a proton transfer reaction time of flight mass spectrometer (PTR-TOF) for 10 Hz EC measurements of full mass spectra up to m/z 315. The mass resolution of the PTR-TOF enabled the identification of chemical formulas and separation of oxygenated and hydrocarbon species exhibiting the same nominal mass. We determined 481 ion mass peaks from ambient air concentration above a managed, temperate mountain grassland in Neustift, Stubai Valley, Austria. During harvesting we found significant fluxes of 18 compounds distributed over 43 ions, including protonated parent compounds, as well as their isotopes and fragments and VOC-H + -water clusters. The dominant BVOC fluxes were methanol, acetaldehyde, ethanol, hexenal and other C 6 leaf wound compounds, acetone, acetic acid, monoterpenes and sequiterpenes.
Atmospheric Chemistry and Physics, 2009
As part of a field campaign in the framework of the NitroEurope project, three different instrume... more As part of a field campaign in the framework of the NitroEurope project, three different instruments for atmospheric ammonia (NH 3 ) measurements were operated sideby-side on a managed grassland site in Switzerland: a modified Proton Transfer Reaction Mass Spectrometer (PTR-MS), a GRadient of AErosol and Gases Online Registrator (GRAEGOR), and an Automated Ammonia Analyzer (AiRRmonia). The modified PTR-MS approach is based on chemical ionization of NH 3 using O + 2 instead of H 3 O + as ionizing agent, GRAEGOR and AiRRmonia measure NH + 4 in liquids after absorption of gaseous NH 3 in a rotating wetannular denuder and through a gas permeable membrane, respectively. Bivariate regression slopes using uncorrected data from all three instruments ranged from 0.78 to 0.97 while measuring ambient NH 3 levels between 2 and 25 ppbv during a 5 days intercomparison period. Correlation coefficients r 2 were in the range of 0.79 to 0.94 for hourly average mixing ratios. Observed discrepancies could be partly attributed to temperature effects on the GRAEGOR calibration. Bivariate regression slopes using corrected data were >0.92 with offsets ranging from 0.22 to 0.58 ppbv. The intercomparison demonstrated the potential of PTR-MS to resolve short-time NH 3 fluctuations which could not be measured by the two other slow-response instruments. During conditions favoring condensation in inlet lines, the PTR-MS underestimated NH 3 mixing ratios, underlining the importance of careful inlet designs as an essential component for any inlet-based instrument.
Applied and Environmental Microbiology, 2008
A method for analysis of volatile organic compounds (VOCs) from microbial cultures was establishe... more A method for analysis of volatile organic compounds (VOCs) from microbial cultures was established using proton transfer reaction-mass spectrometry (PTR-MS). A newly developed sampling system was coupled to a PTR-MS instrument to allow on-line monitoring of VOCs in the dynamic headspaces of microbial cultures. The novel PTR-MS method was evaluated for four reference organisms: Escherichia coli, Shigella flexneri, Salmonella enterica, and Candida tropicalis. Headspace VOCs in sampling bottles containing actively growing cultures and uninoculated culture medium controls were sequentially analyzed by PTR-MS. Characteristic marker ions were found for certain microbial cultures: C. tropicalis could be identified by several unique markers compared with the other three organisms, and E. coli and S. enterica were distinguishable from each other and from S. flexneri by specific marker ions, demonstrating the potential of this method to differentiate between even closely related microorganisms. Although the temporal profiles of some VOCs were similar to the growth dynamics of the microbial cultures, most VOCs showed a different temporal profile, characterized by constant or decreasing VOC levels or by single or multiple peaks over 24 h of incubation. These findings strongly indicate that the temporal evolution of VOC emissions during growth must be considered if characterization or differentiation based on microbial VOC emissions is attempted. Our study may help to establish the analysis of VOCs by on-line PTR-MS as a routine method in microbiology and as a tool for monitoring environmental and biotechnological processes.
Grasslands comprise natural tropical savannah over managed temperate fields to tundra and cover o... more Grasslands comprise natural tropical savannah over managed temperate fields to tundra and cover over a quarter of the Earth's land surface. Plant growth, maintenance and decay result in volatile organic compound (VOCs) emissions to the atmosphere. Furthermore, biogenic VOCs (BVOCs) are emitted due to various environmental stresses 5 including cutting and drying during harvesting. Fluxes of BVOCs were measured with a proton-transfer-reaction -mass-spectrometer (PTR-MS) over temperate mountain grassland in Stubai Valley (Tyrol, Austria) over one growing season (2008). VOC fluxes were calculated from the disjunct PTR-MS data using the virtual disjunct eddy covariance method and the gap filling method. The two independent methods ob-10 tained methanol fluxes following a regression line of y=0.94x−0.06 (correlation factor: R 2 =0.94). Methanol showed strong daytime emissions throughout the growing season.
Number of pages (excl. cover sheet): 6 Number of figures: 2 Number of tables: 0 2 3 Figure S1 Tim... more Number of pages (excl. cover sheet): 6 Number of figures: 2 Number of tables: 0 2 3 Figure S1 Time course of BVOC detected by PTR-TOF immediately after wounding plants of T. repens, D. glomerata and R. acris and during the first hour of the desiccation process. Different colors and symbols indicate different protonated mass ions. Green leaves volatiles (GLVs) are shown in panels a, d and g, terpenoid-like compounds in panels b, e and h, and other oxygenated volatiles in panels c, f and i. Letters (L) and (R) in the figure legends indicate that values shown refer to the left and right y-axis, respectively. All the data shown are from a single measurement, but are representative of experiments replicated four times on different individuals from the same plant species.
Atmospheric Chemistry and Physics, 2014
An overview of acetaldehyde exchange above a managed temperate mountain grassland in Austria over... more An overview of acetaldehyde exchange above a managed temperate mountain grassland in Austria over four growing seasons is presented. The meadow acted as a net source of acetaldehyde in all 4 years, emitting between 7 and 28 mg C m −2 over the whole growing period. The cutting of the meadow resulted in huge acetaldehyde emission bursts of up to 16.5 nmol m −2 s −1 on the day of harvesting or 1 day later. During undisturbed conditions both periods with net uptake and net emissions of acetaldehyde were observed. The bidirectional nature of acetaldehyde fluxes was also reflected by clear diurnal cycles during certain time periods, indicating strong deposition processes before the first cut and emission towards the end of the growing season.
Nature, 2013
Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half o... more Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei 1 . Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes 2 . Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases 2 . However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere 3 . It is thought that amines may enhance nucleation 4-16 , but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.
Atmospheric Chemistry and Physics, 2012
We present simultaneous fast, in-situ measurements of formaldehyde and glyoxal from two rural cam... more We present simultaneous fast, in-situ measurements of formaldehyde and glyoxal from two rural campaigns, BEARPEX 2009 and BEACHON-ROCS, both located in Pinus Ponderosa forests with emissions dominated by biogenic volatile organic compounds (VOCs). Despite considerable variability in the formaldehyde and glyoxal concentra-5 tions, the ratio of glyoxal to formaldehyde, R GF , displayed a very regular diurnal cycle over nearly 2 weeks of measurements. The only deviations in R GF were toward higher values and were the result of a biomass burning event during BEARPEX 2009 and very fresh anthropogenic influence during BEACHON-ROCS. Other rapid changes in glyoxal and formaldehyde concentrations have hardly any affect on R GF and could re-10 flect transitions between low and high NO regimes. The trend of increased R GF from both anthropogenic reactive VOC mixtures and biomass burning compared to biogenic reactive VOC mixtures is robust due to the short timescales over which the observed changes in R GF occurred. Satellite retrievals, which suggest higher R GF for biogenic areas, are in contrast to our observed trends. It remains important to address this 15 discrepancy, especially in view of the importance of satellite retrievals and in-situ measurements for model comparison. In addition, we propose that R GF , together with the absolute concentrations of glyoxal and formaldehyde, represents a useful metric for biogenic or anthropogenic reactive VOC mixtures. In particular, R GF yields information about not simply the VOCs in an airmass, but the VOC processing that directly couples 20 ozone and secondary organic aerosol production. et al., 2000), and production of secondary organic aerosol (Dockery et al.,
Atmospheric Chemistry and Physics, 2013
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Papers by R. Schnitzhofer