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Our understanding of formation processes, physical properties, and climate/health effects of organic aerosols is still limited in part due to limited knowledge of organic aerosol composition. We present speciated measurements of organic aerosol composition by two methods: in situ thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and offline two-dimensional gas chromatography with a time-of-flight mass spectrometer (GC x GC/TOF-MS). Using the GC x GC/TOF-MS 153 compounds were identified, 123 of which were matched with 64 ions observed by the TD-PTR-MS. A reasonable overall correlation of 0.67 (r²) was found between the total matched TD-PTR-MS signal (sum of 64 ions) and the total matched GC x GC/TOF-MS signal (sum of 123 compounds) for the Los Angeles area. A reasonable quantitative agreement between the two methods was observed for most individual compounds with concentrations which were detected at levels above 2 ngm-3 using the GC x GC/TOF-MS. The analysis of monocarboxylic acids standards with TD-PTR-MS showed that alkanoic acids with molecular masses below 290 amu are detected well (recovery fractions above 60 %). However, the concentrations of these acids were consistently higher on quartz filters (quantified offline by GC x GC/TOF-MS) than those suggested by in situ TD-PTR-MS measurements, which is consistent with the semivolatile nature of the acids and corresponding positive filter sampling artifacts. [ABSTRACT FROM AUTHOR]

PTRwid is a fast and user friendly tool that has been developed to process data from proton-transfer-reaction time-of-flight mass-spectrometers (PTR-TOF-MS) that use HTOF time-of-flight mass-spectrometers from Tofwerk AG (Switzerland). PTRwid is designed for a comprehensive evaluation of whole laboratory or field based studies. All processing runs autonomously and whole laboratory or field campaigns can, in principle, be processed with a few mouse clicks. Unique features of PTRwid include (i) an autonomous and accurate mass scale calibration, (ii) the computation of an "Unified Mass list" that - in addition to an uniform data structure - provides a robust method to determine the precision of attributed peak masses, and (iii) fast data analysis due to well considered choices in data processing. [ABSTRACT FROM AUTHOR]

Our understanding of formation processes, physical properties and climate/health effects of organic aerosols is still limited in part due to limited knowledge of organic aerosol composition. We present speciated measurements of organic aerosol composition by two methods: in-situ thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and offline two-dimensional gas chromatography with a timeof- flight mass spectrometer (GC×GC/TOF-MS). 153 compounds were identified using the GC×GC/TOF-MS, 123 of which were matched with 64 ions observed by the TDPTR- MS. A reasonable overall correlation of 0.67 (r2) was found between the total 10 matched TD-PTR-MS signal (sum of 64 ions) and the total matched GC×GC/TOF-MS signal (sum of 123 compounds). A reasonable quantitative agreement between the two methods was observed for most individual compounds with concentrations which were detected at levels above 2 ngm-3 using the GC×GC/TOF-MS. The analysis of monocarboxylic acids standards with TD-PTR-MS showed that alkanoic acids with molecular 15 masses below 290 amu are detected well (recovery fractions above 60%). However, the concentrations of these acids were consistently higher on quartz filters (quantified offline by GC×GC/TOF-MS) than those suggested by in-situ TD-PTR-MS measurements, which is consistent with the semivolatile nature of the acids and corresponding positive filter sampling artifacts. [ABSTRACT FROM AUTHOR]

During the CalNex study (15 May to 16 June 2010) a large suite of instruments was operated at the Los Angeles area ground supersite to characterize the sources and atmospheric processing of atmospheric pollution. The thermal-desorption proton-transfer-reaction massspectrometer (TD-PTR-MS) was deployed to an urban area for the first time and detected 691 organic ions in aerosol samples, the mean total concentration of which was estimated as 3.3 µgm-3. Based on comparison to total organic aerosol (OA) measurements, we estimate that approximately 50% of the OA mass at this site was directly measured by the TD-PTR-MS. Based on correlations with aerosol mass spectrometer (AMS) OA components, the ions were grouped to represent hydrocarbon-like OA (HOA), local OA (LOA), semi-volatile oxygenated OA (SV-OOA), and low volatility oxygenated OA (LV-OOA). Mass spectra and thermograms of the ion groups are mostly consistent with the assumed sources and/or photochemical origin of the OA components. The mass spectra of ions representing the primary components HOA and LOA included the highest m/z, consistent with their higher resistance to thermal decomposition, and they were volatilized at lower temperatures (~150 °C). Photochemical ageing weakens C-C bond strengths (also resulting in chemical fragmentation), and produces species of lower volatility (through the addition of functional groups). Accordingly the mass spectra of ions representing the oxidized OA components (SV-OOA, and LV-OOA) lack the highest masses and they are volatilized at higher temperatures (250-300 °NC). Chemical parameters like mean carbon number (nC), mean carbon oxidation state (OSC), and the atomic ratios O/C and H/C of the ion groups are consistent with the expected sources and photochemical processing of the aerosol components. Our data suggest that chemical fragmentation gains importance over functionalization as photochemical age of OA increases. Surprisingly, the photochemical age of OA decreases during the daytime hours, demonstrating the importance of rapid production of new (photochemically young) SV-OOA during daytime. The PTR detects higher organic N concentrations than the AMS, the reasons for which are not well understood and cannot be explained by known artifacts related to PTR or the AMS. The median atomic N/C ratio (6.4 %) of the ion group representing LV-OOA is a factor 2 higher than N/C of any other ion group. This suggests a multiphase chemical source involving ammonium ions is contributing to LV-OOA. [ABSTRACT FROM AUTHOR]

During summer 2010, a proton transfer reaction - time of flight - mass spectrometer (PTR-TOF-MS) and a quadrupole proton transfer reaction mass spectrometer (PTR-MS) were deployed simultaneously for one month in an orange orchard in the Central Valley of California to collect continuous data suitable for eddy covariance (EC) flux calculations. The high time resolution (5 Hz) and high mass resolution (up to 5000 m/Δm) data from the PTR-TOF-MS provided the basis for calculating the concentration and flux for a wide range of volatile organic compounds (VOC). Throughout the campaign, 664 mass peaks were detected in mass-to-charge ratios between 10 and 1278. Here we present PTR-TOF-MS EC fluxes of the 27 ion species for which the vertical gradient was simultaneously measured by PTR-MS. These EC flux data were validated through spectral analysis (i.e., co-spectrum, normalized co-spectrum, and ogive). Based on inter-comparison of the two PTR instruments, no significant instrumental biases were found in either mixing ratios or fluxes, and the data showed agreement within 5% on average for methanol and acetone. For the measured biogenic volatile organic compounds (BVOC), the EC fluxes from PTR-TOF-MS were in agreement with the qualitatively inferred flux directions from vertical gradient measurements by PTR-MS. For the 27 selected ion species reported here, the PTR-TOF-MS measured total (24 h) mean net flux of 299 μg C m-2 h-1. The dominant BVOC emissions from this site were monoterpenes (m/z 81.070 +m/z 137.131 +m/z 95.086, 34 %, 102 μg C m-2 h-1) and methanol (m/z 33.032, 18 %, 72 μgC m-2 h-1). The next largest fluxes were detected at the following masses (attribution in parenthesis): m/z 59.048 (mostly acetone, 12.2 %, 36.5 μgC m-2 h-1), m/z 61.027 (mostly acetic acid, 11.9 %, 35.7 μg C m-2 h-1), m/z 93.069 (para-cymene + toluene, 4.1 %, 12.2 μgC m-2 h-1), m/z 45.033 (acetaldehyde, 3.8 %, 11.5 μgC m-2 h-1), m/z 71.048 (methylvinylketone + methacrolein, 2.4 %, 7.1 μgC m-2 h-1), and m/z 69.071 (isoprene + 2-methyl- 3-butene-2-ol, 1.8 %, 5.3 μg C m-2 h-1). Low levels of emission and/or deposition (<1.6% for each, 5.8% in total flux) were observed for the additional reported masses. Overall, our results show that EC flux measurements using PTR-TOFMS is a powerful new tool for characterizing the biosphereatmosphere exchange including both emission and deposition for a large range of BVOC and their oxidation products. [ABSTRACT FROM AUTHOR]

Many monoterpenes have been identified in forest emissions using gas chromatography (GC). Until now, it has been impossible to determine whether all monoterpenes are appropriately measured using GC techniques. We used a proton transfer reaction mass spectrometer (PTR-MS) coupled with the eddy covariance (EC) technique to measure mixing ratios and fluxes of total monoterpenes above a ponderosa pine plantation. We compared PTR-MS-EC results with simultaneous measurements of eight speciated monoterpenes, β-pinene, α-pinene, 3-carene, d-limonene, β-phellandrene, α-terpinene, camphene, and terpinolene, made with an automated, in situ gas chromatograph with flame ionization detectors (GC-FID), coupled to a relaxed eddy accumulation system (REA). Monoterpene mixing ratios and fluxes measured by PTR-MS averaged 30±2.3% and 31±9.2% larger than by GC-FID, with larger mixing ratio discrepancies between the two techniques at night than during the day. Two unidentified peaks that correlated with β-pinene were resolved in the chromatograms and completely accounted for the daytime difference and reduced the nighttime mixing ratio difference to 20±2.9%. Measurements of total monoterpenes by PTR-MS-EC indicated that GC-FID-REA measured the common, longer-lived monoterpenes well, but that additional terpenes were emitted from the ecosystem that represented an important contribution to the total mixing ratio above the forest at night. [ABSTRACT FROM AUTHOR]

Airborne measurements of acetone, methanol, PAN, acetonitrile (by Proton Transfer Reaction Mass Spectrometry), and CO (by Tunable Diode Laser Absorption Spectroscopy) have been performed during the Mediterranean Intensive Oxidants Study (MINOS August 2001). We have identified ten biomass burning plumes from strongly elevated acetonitrile mixing ratios. The characteristic biomass burning signatures obtained from these plumes reveal secondary production of acetone and methanol, while CO photochemically declines in the plumes. Mean excess mixing ratios -- normalized to CO -- of 1.8%, 0.20%, 3.8%, and 0.65% for acetone, acetonitrile, methanol, and PAN, respectively, were found. By scaling to an assumed global annual source of 663--807 Tg CO, biomass burning emissions of 25--31 and 29--35 Tg/yr for acetone and methanol are estimated, respectively. Our measurements suggest that the present biomass burning contributions of acetone and methanol are significantly underestimated due to the neglect of secondary formation within the plume. Median acetonitrile mixing ratios throughout the troposphere were around 150 pmol/mol, in accord with current biomass burning inventories and an atmospheric lifetime of ∼6 months. [ABSTRACT FROM AUTHOR]

We present a novel approach to study the organic composition of aerosol filter samples using thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) in the laboratory. The method is tested and validated based on the comparison with in situ TD-PTR-MS measurements. In general, we observe correspondence within the levels of uncertainty between in situ and offline TD-PTR-MS measurements for compounds desorbing at temperatures above 100 °C and for quartz fiber filters that were sampled for more than one day. Positive sampling artifacts (50–80%, with respect to the in situ measurements) from adsorption of semivolatile organic gas phase compounds are apparent on filters sampled for one day. Detailed chemical analysis shows that these positive sampling artifacts are likely caused by primary emissions that have not been strongly oxidized. Negative sampling artifacts (7–35%, with respect to the in situ measurements) are observed for most filters sampled for two and three days, and potentially caused by incomplete desorption of aerosols (in particular, nitrogen-containing organics) from the filters during the offline measurements and chemical reactions on the filters. [ABSTRACT FROM AUTHOR]

Numerous volatile organic compounds (VOCs) exist in Earth's atmosphere, most of which originate from biogenic emissions. Despite VOCs' critical role in tropospheric chemistry, studies for evaluating their atmosphere-ecosystem exchange (emission and deposition) have been limited to a few dominant compounds owing to a lack of appropriate measurement techniques. Using a high-mass resolution proton transfer reaction-time of flight-mass spectrometer and an absolute value eddy-covariance method, we directly measured 186 organic ions with net deposition, and 494 that have bidirectional flux. This observation of active atmosphere-ecosystem exchange of the vast majority of detected VOCs poses a challenge to current emission, air quality, and global climate models, which do not account for this extremely large range of compounds. This observation also provides new insight for understanding the atmospheric VOC budget. [ABSTRACT FROM AUTHOR]