We evaluate the performance of a new chemical ionization source called Vocus, consisting of a discharge reagent-ion source and focusing ion–molecule reactor (FIMR) for use in proton-transfer-reaction ...time-of-flight mass spectrometry (PTR-TOF) measurements of volatile organic compounds (VOCs) in air. The reagent ion source uses a low-pressure discharge. The FIMR consists of a glass tube with a resistive coating, mounted inside a radio frequency (RF) quadrupole. The axial electric field is used to enhance ion collision energies and limit cluster ion formation. The RF field focuses ions to the central axis of the reactor and improves the detection efficiency of product ions. Ion trajectory calculations demonstrate the mass-dependent focusing of ions and enhancement of the ion collision energy by the RF field, in particular for the lighter ions. Product ion signals are increased by a factor of 10 when the RF field is applied (5000–18 000 cps ppbv–1), improving measurement precision and detection limits while operating at very similar reaction conditions as traditional PTR instruments. Because of the high water mixing ratio in the FIMR, we observe no dependence of the sensitivity on ambient sample humidity. In this work, the Vocus is interfaced to a TOF mass analyzer with a mass resolving power up to 12 000, which allows clear separation of isobaric ions, observed at nearly every nominal mass when measuring ambient air. Measurement response times are determined for a range of ketones with saturation vapor concentrations down to 5 × 104 μg m–3 and compare favorably with previously published results for a PTR-MS instrument.
Abstract
It is now established that microplastics are a pervasive presence in aquatic and terrestrial ecosystems. The same is assumed to be true for nanoplastics but data are lacking due to technical ...difficulties associated with sample analysis. Here, we measured nanoplastics in waterbodies at two contrasting sites: remote Siberian Arctic tundra and a forest landscape in southern Sweden. Nanoplastics were detected in all sampled Swedish lakes (
n
= 7) and streams (
n
= 4) (mean concentration = 563
µ
g l
−1
) and four polymer types were identified (polyethylene, polyvinyl chloride (PVC), polypropylene, polyethylene terephthalate). In Siberia nanoplastics were detected in 7/12 sampled lakes, ponds and surface flooding, but only two polymer types were detected (PVC and polystyrene) and concentrations were lower (mean 51
µ
g l
−1
). Based on back-calculation of air mass trajectories and particle dispersion, we infer that nanoplastics arrive at both sites by aerial deposition from local and regional sources. Our results suggest that nanoplastics may be a near-ubiquitous presence even in remote ecosystems.
Warming in the Arctic accelerates thawing of permafrost-affected soils, which leads to a release of greenhouse gases to the atmosphere. We do not know whether permafrost thaw also releases ...non-methane volatile organic compounds that can contribute to both negative and positive radiative forcing on climate. Here we show using proton transfer reaction-time of flight-mass spectrometry that substantial amounts of ethanol and methanol and in total 316 organic ions were released from Greenlandic permafrost soils upon thaw in laboratory incubations. We demonstrate that the majority of this release is taken up in the active layer above. In an experiment using
C-labeled ethanol and methanol, we demonstrate that these compounds are consumed by microorganisms. Our findings highlight that the thawing permafrost soils are not only a considerable source of volatile organic compounds but also that the active layer regulates their release into the atmosphere.
There are few long-term datasets of volatile organic compounds (VOCs) in the High Arctic. Furthermore, knowledge about their source regions remains
lacking. To address this matter, we report a ...multiseason dataset of highly time-resolved VOC measurements in the High Arctic from April to October
2018. We have utilized a combination of measurement and modeling techniques to characterize the mixing ratios, temporal patterns, and sources of
VOCs at the Villum Research Station at Station Nord in northeastern Greenland. Atmospheric VOCs were measured using proton-transfer-reaction time-of-flight mass
spectrometry. Ten ions were selected for source apportionment with the positive matrix factorization (PMF) receptor model. A
four-factor solution to the PMF model was deemed optimal. The factors identified were biomass burning, marine cryosphere, background, and Arctic
haze. The biomass burning factor described the variation of acetonitrile and benzene and peaked during August and September. The marine cryosphere
factor was comprised of carboxylic acids (formic, acetic, and C3H6O2) as well as dimethyl sulfide (DMS). This factor displayed peak
contributions during periods of snow and sea ice melt. A potential source contribution function (PSCF) showed that the source regions for this
factor were the coasts around southeastern and northeastern Greenland. The background factor was temporally ubiquitous, with a slight decrease in
the summer. This factor was not driven by any individual chemical species. The Arctic haze factor was dominated by benzene with contributions from
oxygenated VOCs. This factor exhibited a maximum in the spring and minima during the summer and autumn. This temporal pattern and species profile
are indicative of anthropogenic sources in the midlatitudes. This study provides seasonal characteristics and sources of VOCs and can help
elucidate the processes affecting the atmospheric chemistry and biogeochemical feedback mechanisms in the High Arctic.
Display omitted
•Methylsiloxanes were identified in aerosols emitted by a ship.•The natural abundance of silicon isotopes can be used to identify methylsiloxanes in high resolution mass ...spectrometry.•Particulate-phase methylsiloxanes were mainly emitted near the harbor under inefficient combustion conditions.•Considerably lower methylsiloxane emissions were observed under cruise conditions.
The chemical and stable carbon isotopic composition of the organic aerosol particles (OA) emitted by a shuttle passenger ship between mainland Naples and island Capri in Italy were investigated. Various methylsiloxanes and derivatives were found in particulate ship emissions for the first time, as identified in the mass spectra of a thermal desorption – proton transfer reaction – mass spectrometer (TD-PTR-MS) based on the natural abundance of silicon isotopes. Large contributions of methylsiloxanes to OA (up to 59.3%) were found under inefficient combustion conditions, and considerably lower methylsiloxane emissions were observed under cruise conditions (1.2% of OA). Furthermore, the stable carbon isotopic composition can provide a fingerprint for methylsiloxanes, as they have low δ13C values in the range of −44.91‰ ± 4.29‰. The occurrence of methylsiloxanes was therefore further supported by low δ13C values of particulate organic carbon (OC), ranging from −34.7‰ to −39.4‰, when carbon fractions of methylsiloxanes in OC were high. The δ13C values of OC increased up to around −26.7‰ under cruise conditions, when carbon fractions of methylsiloxanes in OC were low. Overall, the δ13C value of OC decreased linearly with increasing carbon fraction of methylsiloxanes in OC, and the slope is consistent with a mixture of methylsiloxanes and fuel combustion products. The methylsiloxanes in ship emissions may come from engine lubricants.
Abstract Microplastics and nanoplastics are hazardous to ecosystems, wildlife, and through seafood, also for human health. Due to biological, chemical, and physical characteristics, nanoplastics can ...slip through cell membranes, being even more toxicologically important than microplastics. Thermal Desorption - Proton Transfer Reaction - Mass Spectrometry was used to analyze mussels from the Apulian region, Italy. All the analyzed organisms have plastics (values ranging from 10 to 187 ng of microplastics and nanoplastics per dry weight mg). The highest mass of plastics was detected in the size groups >2.2 µm (218 ng per dry weight mg) and 20–200 nm (187 ng per dry weight mg). Upscaling data we estimated that people in Europe could ingest more than 2 mg of nanoplastics per year through seafood consumption. The detected presence of nanoplastics in farmed mussels here presented contributes to establishing a baseline for monitoring these pollutants.
This study reports emission of organic particulate matter by light-duty vehicles (LDVs) and heavy-duty vehicles (HDVs) in the city of São Paulo, Brazil, where vehicles run on three different fuel ...types: gasoline with 25 % ethanol (called gasohol, E25), hydrated ethanol (E100), and diesel (with 5 % biodiesel). The experiments were performed at two tunnels: Jânio Quadros (TJQ), where 99 % of the vehicles are LDVs, and RodoAnel Mário Covas (TRA), where up to 30 % of the fleet are HDVs. Fine particulate matter (PM2.5) samples were collected on quartz filters in May and July 2011 at TJQ and TRA, respectively. The samples were analyzed by thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and by thermal–optical transmittance (TOT). Emission factors (EFs) for organic aerosol (OA) and organic carbon (OC) were calculated for the HDV and the LDV fleet. We found that HDVs emitted more PM2.5 than LDVs, with OC EFs of 108 and 523 mg kg−1 burned fuel for LDVs and HDVs, respectively. More than 700 ions were identified by TD-PTR-MS and the EF profiles obtained from HDVs and LDVs exhibited distinct features. Unique organic tracers for gasoline, biodiesel, and tire wear have been tentatively identified. nitrogen-containing compounds contributed around 20 % to the EF values for both types of vehicles, possibly associated with incomplete fuel burning or fast secondary production. Additionally, 70 and 65 % of the emitted mass (i.e. the OA) originates from oxygenated compounds from LDVs and HDVs, respectively. This may be a consequence of the high oxygen content of the fuel. On the other hand, additional oxygenation may occur during fuel combustion. The high fractions of nitrogen- and oxygen-containing compounds show that chemical processing close to the engine / tailpipe region is an important factor influencing primary OA emission. The thermal-desorption analysis showed that HDVs emitted compounds with higher volatility, and with mainly oxygenated and longer chain hydrocarbons than LDVs.
► Leaf litter of several halophyte species emits methyl chloride, but the emission rates vary largely between plant species. ► The emission rates were not correlated to the chloride- and methoxyl ...group content of the leaf material. ► The temperature dependence of the emission rates was similar for all investigated plant species.
Methyl chloride (CH3Cl) is the most abundant natural chlorine containing compound in the atmosphere, and responsible for a significant fraction of stratospheric ozone destruction. Understanding the global CH3Cl budget is therefore of great importance. However, the strength of the individual sources and sinks is still uncertain. Leaf litter is a potentially important source of methyl chloride, but factors controlling the emissions are unclear. This study investigated CH3Cl emissions from leaf litter of twelve halophyte species. The emissions were not due to biological activity, and emission rates varied between halophyte species up to two orders of magnitude. For all species, the CH3Cl emission rates increased with temperature following the Arrhenius relation. Activation energies were similar for all investigated plant species, indicating that even though emissions vary largely between plant species, their response to changing temperatures is similar. The chloride and methoxyl group contents of the leaf litter samples were determined, but those parameters were not significantly correlated to the CH3Cl emission rate.
An intercomparison of different aerosol chemical characterization techniques has been performed as part of a chamber study of biogenic secondary organic aerosol (BSOA) formation and aging at the ...atmosphere simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). Three different aerosol sampling techniques – the aerosol collection module (ACM), the chemical analysis of aerosol online (CHARON) and the collection thermal-desorption unit (TD) were connected to proton transfer reaction time-of-flight mass spectrometers (PTR-ToF-MSs) to provide chemical characterization of the SOA. The techniques were compared among each other and to results from an aerosol mass spectrometer (AMS) and a scanning mobility particle sizer (SMPS). The experiments investigated SOA formation from the ozonolysis of β-pinene, limonene, a β-pinene–limonene mix and real plant emissions from Pinus sylvestris L. (Scots pine). The SOA was subsequently aged by photo-oxidation, except for limonene SOA, which was aged by NO3 oxidation. Despite significant differences in the aerosol collection and desorption methods of the PTR-based techniques, the determined chemical composition, i.e. the same major contributing signals, was found by all instruments for the different chemical systems studied. These signals could be attributed to known products expected from the oxidation of the examined monoterpenes. The sampling and desorption method of ACM and TD provided additional information on the volatility of individual compounds and showed relatively good agreement. Averaged over all experiments, the total aerosol mass recovery compared to an SMPS varied within 80 ± 10, 51 ± 5 and 27 ± 3 % for CHARON, ACM and TD, respectively. Comparison to the oxygen-to-carbon ratios (O : C) obtained by AMS showed that all PTR-based techniques observed lower O : C ratios, indicating a loss of molecular oxygen either during aerosol sampling or detection. The differences in total mass recovery and O : C between the three instruments resulted predominantly from differences in the field strength (E∕N) in the drift tube reaction ionization chambers of the PTR-ToF-MS instruments and from dissimilarities in the collection/desorption of aerosols. Laboratory case studies showed that PTR-ToF-MS E∕N conditions influenced fragmentation which resulted in water and further neutral fragment losses of the detected molecules. Since ACM and TD were operated in higher E∕N than CHARON, this resulted in higher fragmentation, thus affecting primarily the detected oxygen and carbon content and therefore also the mass recovery. Overall, these techniques have been shown to provide valuable insight on the chemical characteristics of BSOA and can address unknown thermodynamic properties such as partitioning coefficient values and volatility patterns down to a compound-specific level.
PDF
