VOC–OHM: A new technique for rapid measurements of ambient total OH reactivity and volatile organic compounds using a single proton transfer reaction mass spectrometer

Kumar, Vinod; Sinha, Vinayak

doi:10.1016/j.ijms.2014.10.012

Cited by 31 publications

(43 citation statements)

References 28 publications

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“…The OH reactivity was on average 5 ± 4 s −1 (1σ ) with a maximum value of 17 ± 6 s −1 (35 % uncertainty). The observed maximum is comparable to values of OH reactivity measured at forested locations in northern latitudes (temperate and boreal forests as reported by Di Carlo et al, 2004;Ren et al, 2006;Sinha et al, 2010;Noelscher et al, 2013;Kumar and Sinha, 2014;Nakashima et al, 2014). This finding highlights the importance of primary emitted biogenic VOCs on the OH reactivity, especially where air temperature and solar radiation are high, even though our site was specifically selected for a focused study on mixed and aged continental air masses reaching the basin.…”

Section: Discussionsupporting

confidence: 87%

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

et al. 2017

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Abstract. Total hydroxyl radical (OH) reactivity, the total loss frequency of the hydroxyl radical in ambient air, provides the total loading of OH reactants in air. We measured the total OH reactivity for the first time during summertime at a coastal receptor site located in the western Mediterranean Basin. Measurements were performed at a temporary field site located in the northern cape of Corsica (France), during summer 2013 for the project CARBOSOR (CARBOn within continental pollution plumes: SOurces and Reactivity)-ChArMEx (Chemistry and Aerosols Mediterranean Experiment). Here, we compare the measured total OH reactivity with the OH reactivity calculated from the measured reactive gases. The difference between these two parameters is termed missing OH reactivity, i.e., the fraction of OH reactivity not explained by the measured compounds. The total OH reactivity at the site varied between the instrumental LoD (limit of detection = 3 s −1 ) to a maximum of 17 ± 6 s −1 (35 % uncertainty) and was 5 ± 4 s −1 (1σ SDstandard deviation) on average. It varied with air temperature exhibiting a diurnal profile comparable to the reactivity calculated from the concentration of the biogenic volatile organic compounds measured at the site. For part of the campaign, 56 % of OH reactivity was unexplained by the measured OH reactants (missing reactivity). We suggest that oxidation products of biogenic gas precursors were among the contributors to missing OH reactivity.

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Section: Discussionsupporting

confidence: 87%

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

et al. 2017

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“…For example, the observed ranking in oxygenated VOCs is different from the ranking observed during wintertime in megacities like Paris and London (methanol > acetaldehyde > acetone) (Dolgorouky et al, 2012;Langford et al, 2010). Furthermore the ranking observed for aromatic VOCs during this study (benzene > toluene > sum of C8aromatics > sum of C9-aromatics) was in contrast to the ranking (toluene > benzene > sum of C8-aromatics > sum of C9-aromatics) observed in several urban sites such as Paris, London and Tokyo (Dolgorouky et al, 2012;Langford et al, 2010;Yoshino et al, 2012). This exemplifies that the nature and strength of emission sources for oxygenated and aromatic VOCs in the Kathmandu Valley differ from several urban areas in other parts of the world.…”

Section: General Trends In Voc Concentrations During Thementioning

confidence: 81%

“…This points to the fact that the major sources of oxygenated VOCs during wintertime in Kathmandu are different from what are generally considered to be the most important sources based on studies conducted in several other regions of the world, where photooxidation and industrial sources dominate and have large implications for wintertime oxidation chemistry in the valley, as these species play a key role in radical chemistry (Singh et al, 1995). For example, the observed ranking in oxygenated VOCs is different from the ranking observed during wintertime in megacities like Paris and London (methanol > acetaldehyde > acetone) (Dolgorouky et al, 2012;Langford et al, 2010). Furthermore the ranking observed for aromatic VOCs during this study (benzene > toluene > sum of C8aromatics > sum of C9-aromatics) was in contrast to the ranking (toluene > benzene > sum of C8-aromatics > sum of C9-aromatics) observed in several urban sites such as Paris, London and Tokyo (Dolgorouky et al, 2012;Langford et al, 2010;Yoshino et al, 2012).…”

Section: General Trends In Voc Concentrations During Thementioning

confidence: 98%

Overview of VOC emissions and chemistry from PTR-TOF-MS measurements during the SusKat-ABC campaign: high acetaldehyde, isoprene and isocyanic acid in wintertime air of the Kathmandu Valley

et al. 2016

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The Kathmandu Valley in Nepal suffers from severe wintertime air pollution. Volatile organic compounds (VOCs) are key constituents of air pollution, though their specific role in the valley is poorly understood due to insufficient data. During the SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) field campaign conducted in Nepal in the winter of 2012-2013, a comprehensive study was carried out to characterise the chemical composition of ambient Kathmandu air, including the determination of speciated VOCs, by deploying a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) -the first such deployment in South Asia. In the study, 71 ion peaks (for which measured ambient concentrations exceeded the 2σ detection limit) were detected in the PTR-TOF-MS mass scan data, highlighting the chemical complexity of ambient air in the valley. Of the 71 species, 37 were found to have campaign average concentrations greater than 200 ppt and were identified based on their spectral characteristics, ambient diel profiles and correlation with specific emission tracers as a result of the high mass resolution (m / m > 4200) and temporal resolution (1 min) of the PTR-TOF-MS. The concentration ranking in the average VOC mixing ratios dur-ing our wintertime deployment was acetaldehyde (8.8 ppb) > methanol (7.4 ppb) > acetone + propanal (4.2 ppb) > benzene (2.7 ppb) > toluene (1.5 ppb) > isoprene (1.1 ppb) > acetonitrile (1.1 ppb) > C8-aromatics (∼1 ppb) > furan (∼0.5 ppb) > C9-aromatics (0.4 ppb). Distinct diel profiles were observed for the nominal isobaric compounds isoprene (m / z = 69.070) and furan (m / z = 69.033). Comparison with wintertime measurements from several locations elsewhere in the world showed mixing ratios of acetaldehyde (∼ 9 ppb), acetonitrile (∼ 1 ppb) and isoprene (∼ 1 ppb) to be among the highest reported to date. Two "new" ambient compounds, namely formamide (m / z = 46.029) and acetamide (m / z = 60.051), which can photochemically produce isocyanic acid in the atmosphere, are reported in this study along with nitromethane (a tracer for diesel exhaust), which has only recently been detected in ambient studies. Two distinct periods were selected during the campaign for detailed analysis: the first was associated with high wintertime emissions of biogenic isoprene and the second with elevated levels of ambient acetonitrile, benzene and isocyanic acid from biomass burning activities. Emissions from biomass burning and biomass co-fired brick kilns were found to be the dominant sources for compounds such Published by Copernicus Publications on behalf of the European Geosciences Union. C. Sarkar et al.: Wintertime high acetaldehyde, isoprene and isocyanic acid in Kathmandu Valleyas propyne, propene, benzene and propanenitrile, which correlated strongly with acetonitrile (r 2 > 0.7), a chemical tracer for biomass burning. The calculated total VOC OH reactivity was dominated by acetaldehyde (24.0 %), isoprene (20.2 %) and propene (18.7 %), while oxygenated VOCs and is...

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“…This can be used to determine ozone production regimes on local and regional scales and to calculate instantaneous ozone production rates as shown for the DOMINO field campaign . More recently, Kumar and Sinha (2014) have shown that CRM coupled to sequential ambient VOC measurements using a new "VOC-OHM" system can be used to constrain the rate coefficient of the reactive nominal isobaric compound contributing to a given m/z ratio (e.g. isoprene and furan at m/z = 69), adding more specificity to mass spectrometers with unity mass resolution.…”

Section: Introductionmentioning

confidence: 99%

Intercomparison of the comparative reactivity method (CRM) and pump–probe technique for measuring total OH reactivity in an urban environment

et al. 2015

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Abstract. The investigation of hydroxyl radical (OH) chemistry during intensive field campaigns has led to the development of several techniques dedicated to ambient measurements of total OH reactivity, which is the inverse of the OH lifetime. Three techniques are currently used during field campaigns, including the total OH loss rate method, the pump-probe method, and the comparative reactivity method. However, no formal intercomparison of these techniques has been published so far, and there is a need to ensure that measurements of total OH reactivity are consistent among the different techniques.An intercomparison of two OH reactivity instruments, one based on the comparative reactivity method (CRM) and the other based on the pump-probe method, was performed in October 2012 in a NO x -rich environment, which is known to be challenging for the CRM technique. This study presents an extensive description of the two instruments, the CRM instrument from Mines Douai (MD-CRM) and the pumpprobe instrument from the University of Lille (UL-FAGE), and highlights instrumental issues associated with the two techniques.It was found that the CRM instrument used in this study underestimates ambient OH reactivity by approximately 20 % due to the photolysis of volatile organic compounds (VOCs) inside the sampling reactor; this value is dependent on the position of the lamp within the reactor. However, this issue can easily be fixed, and the photolysis of VOCs was successfully reduced to a negligible level after this intercomparison campaign. The UL-FAGE instrument may also underestimate ambient OH reactivity due to the difficulty to accurately measure the instrumental zero. It was found that the measurements are likely biased by approximately 2 s −1 , due to impurities in humid zero air.Two weeks of ambient sampling indicate that the measurements performed by the two OH reactivity instruments are in agreement, within the measurement uncertainties for each instrument, for NO x mixing ratios up to 100 ppbv. The CRM technique has hitherto mainly been used in low-NO x environments, i.e. environments with ambient NO x mixing ratios lower than a few ppbv, due to a measurement artifact generated by ambient NO inside the sampling reactor. However, this study shows that this technique can also be used under NO x -rich conditions if a NO x -dependent correction is carefully applied on the OH reactivity measurements.A full suite of 52 VOCs, NO x , and other inorganic species were monitored during this intercomparison. An investigation of the OH reactivity budget for this urban site suggests that this suite of trace gases can account for the measured total OH reactivity.

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VOC–OHM: A new technique for rapid measurements of ambient total OH reactivity and volatile organic compounds using a single proton transfer reaction mass spectrometer

Cited by 31 publications

References 28 publications

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

Overview of VOC emissions and chemistry from PTR-TOF-MS measurements during the SusKat-ABC campaign: high acetaldehyde, isoprene and isocyanic acid in wintertime air of the Kathmandu Valley

Intercomparison of the comparative reactivity method (CRM) and pump–probe technique for measuring total OH reactivity in an urban environment

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