scholarly journals Speciation of OH reactivity above the canopy of an isoprene-dominated forest

2016 ◽  
Vol 16 (14) ◽  
pp. 9349-9359 ◽  
Author(s):  
J. Kaiser ◽  
K. M. Skog ◽  
K. Baumann ◽  
S. B. Bertman ◽  
S. B. Brown ◽  
...  
Keyword(s):  
Early Morning ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Oh Radical ◽  
Southeast United States ◽  
Reactive Carbon ◽  
Additional Constant ◽  
Measurement Suite ◽  
Primary Emissions ◽  
Comprehensive Measurement

Abstract. Measurements of OH reactivity, the inverse lifetime of the OH radical, can provide a top–down estimate of the total amount of reactive carbon in an air mass. Using a comprehensive measurement suite, we examine the measured and modeled OH reactivity above an isoprene-dominated forest in the southeast United States during the 2013 Southern Oxidant and Aerosol Study (SOAS) field campaign. Measured and modeled species account for the vast majority of average daytime reactivity (80–95 %) and a smaller portion of nighttime and early morning reactivity (68–80 %). The largest contribution to total reactivity consistently comes from primary biogenic emissions, with isoprene contributing ∼  60 % in the afternoon, and ∼  30–40 % at night and monoterpenes contributing ∼  15–25 % at night. By comparing total reactivity to the reactivity stemming from isoprene alone, we find that ∼  20 % of the discrepancy is temporally related to isoprene reactivity, and an additional constant ∼  1 s−1 offset accounts for the remaining portion. The model typically overestimates measured OVOC concentrations, indicating that unmeasured oxidation products are unlikely to influence measured OH reactivity. Instead, we suggest that unmeasured primary emissions may influence the OH reactivity at this site.

scholarly journals Speciation of OH reactivity above the canopy of an isoprene-dominated forest

2016 ◽  
Author(s):  
J. Kaiser ◽  
K. M. Skog ◽  
K. Baumann ◽  
S. B. Bertman ◽  
S. B. Brown ◽  
...  
Keyword(s):  
Oxidation Products ◽  
Ozone Production ◽  
Biogenic Emissions ◽  
Absolute Value ◽  
Reactive Carbon ◽  
Volatile Organic ◽  
Measurement Suite ◽  
Primary Emissions ◽  
Comprehensive Measurement ◽  
Good Agreement

Abstract. Measurements of OH reactivity, the inverse lifetime of the OH-radical, can provide a top-down estimate of the total amount of reactive carbon in an airmass. Because OH reactivity is tied to the RO2 production rate, the absolute value of OH reactivity has direct implications for ozone production. Additionally, as molecular structure determines volatility, the speciation of reactivity affects the production of secondary organic aerosol (SOA). Several studies have focused on the agreement of measured and calculated or modeled OH reactivity above and within the canopy of isoprene-dominated forests, as well as the relative contributions of volatile organic compounds (VOCs) and oxidized VOCs (OVOCs). Drawing definitive conclusions about the identity of the missing OH reactivity has been limited by the availability of VOC and OVOC measurements. In this work, using a comprehensive measurement suite, we examine the measured and modeled OH reactivity above an isoprene-dominated forest in the South East United States during the 2013 Southern Oxidant and Aerosol Study (SOAS) field campaign. We find good agreement between measured and modeled OH reactivity, with the largest contribution consistently coming from primary biogenic emissions. In contrast, there are small but significant discrepancies in the increase in OH reactivity per isoprene. As the model typically overestimates OVOCs, we do not attribute this discrepancy to unmeasured oxidation products. Instead, we suggest that unmeasured primary emissions may influence the OH reactivity at this site.

Investigating the NO-dependent photooxidation of limonene by OH and O3 using the atmosphere simulation chamber SAPHIR

2021 ◽  
Author(s):  
Yat Sing Pang ◽  
Martin Kaminski ◽  
Anna Novelli ◽  
Philip Carlsson ◽  
Ismail-Hakki Acir ◽  
...  
Keyword(s):  
Organic Aerosol ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Reaction Pathways ◽  
Oh Radicals ◽  
Oh Radical ◽  
Simulation Experiments ◽  
Master Chemical Mechanism ◽  
Simulation Results ◽  
Atmosphere Simulation Chamber

<p>Limonene is the fourth-most abundant monoterpene in the atmosphere, which upon oxidation leads to the formation of secondary organic aerosol (SOA) and thereby influences climate and air quality.</p><p>In this study, the oxidation of limonene by OH at different atmospherically relevant NO and HO<sub>2</sub> levels (NO: 0.1 – 10 ppb; HO<sub>2</sub>: 20 ppt) was investigated in simulation experiments in the SAPHIR chamber at Forschungszentrum Jülich. The analysis focuses on comparing measured radical concentrations (RO<sub>2</sub>, HO<sub>2</sub>, OH) and OH reactivity (k<sub>OH</sub>) with modeled values calculated using the Master Chemical Mechanism (MCM) version 3.3.1.</p><p>At high and medium NO concentrations, RO<sub>2</sub> is expected to quickly react with NO. An HO<sub>2</sub> radical is produced during the process that can be converted back to an OH radical by another reaction with NO. Consistently, for experiments conducted at medium NO levels (~0.5 ppb, RO<sub>2</sub> lifetime ~10 s), simulated RO<sub>2</sub>, HO<sub>2</sub>, and OH agree with observations within the measurement uncertainties, if the OH reactivity of oxidation products is correctly described.</p><p>At lower NO concentrations, the regeneration of HO<sub>2</sub> in the RO<sub>2</sub> + NO reaction is slow and the reaction of RO<sub>2</sub> with HO<sub>2</sub> gains importance in forming peroxides. However, simulation results show a large discrepancy between calculated radical concentrations and measurements at low NO levels (<0.1 ppb, RO<sub>2</sub> lifetime ~ 100 s). Simulated RO<sub>2</sub> concentrations are found to be overestimated by a factor of three; simulated HO<sub>2</sub> concentrations are underestimated by 50 %; simulated OH concentrations are underestimated by about 35%, even if k<sub>OH</sub> is correctly described. This suggests that there could be additional RO<sub>2</sub> reaction pathways that regenerate HO<sub>2</sub> and OH radicals become important, but they are not taken into account in the MCM model.</p>

scholarly journals Terpenes and their oxidation products in the French Landes forest: insights from Vocus PTR-TOF measurements

2020 ◽  
Vol 20 (4) ◽  
pp. 1941-1959 ◽  
Author(s):  
Haiyan Li ◽  
Matthieu Riva ◽  
Pekka Rantala ◽  
Liine Heikkinen ◽  
Kaspar Daellenbach ◽  
...  
Keyword(s):  
Gas Phase ◽  
Detection Efficiency ◽  
Ambient Air ◽  
Reaction Rates ◽  
Early Morning ◽  
Oxidation Products ◽  
Atmospheric Oxidation ◽  
Organic Nitrates ◽  
Reaction Products ◽  
Wide Range

Abstract. The capabilities of the recently developed Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF) are reported for the first time based on ambient measurements. With the deployment of the Vocus PTR-TOF, we present an overview of the observed gas-phase (oxygenated) molecules in the French Landes forest during summertime 2018 and gain insights into the atmospheric oxidation of terpenes, which are emitted in large quantities in the atmosphere and play important roles in secondary organic aerosol production. Due to the greatly improved detection efficiency compared to conventional PTR instruments, the Vocus PTR-TOF identifies a large number of gas-phase signals with elemental composition categories including CH, CHO, CHN, CHS, CHON, CHOS, and others. Multiple hydrocarbons are detected, with carbon numbers up to 20. Particularly, we report the first direct observations of low-volatility diterpenes in the ambient air. The diurnal cycle of diterpenes is similar to that of monoterpenes and sesquiterpenes but contrary to that of isoprene. Various types of terpene reaction products and intermediates are also characterized. Generally, the more oxidized products from terpene oxidations show a broad peak in the day due to the strong photochemical effects, while the less oxygenated products peak in the early morning and/or in the evening. To evaluate the importance of different formation pathways in terpene chemistry, the reaction rates of terpenes with main oxidants (i.e., hydroxyl radical, OH; ozone, O3; and nitrate radical, NO3) are calculated. For the less oxidized non-nitrate monoterpene oxidation products, their morning and evening peaks have contributions from both O3- and OH-initiated monoterpene oxidation. For the monoterpene-derived organic nitrates, oxidations by O3, OH, and NO3 radicals all contribute to their formation, with their relative roles varying considerably over the course of the day. Through a detailed analysis of terpene chemistry, this study demonstrates the capability of the Vocus PTR-TOF in the detection of a wide range of oxidized reaction products in ambient and remote conditions, which highlights its importance in investigating atmospheric oxidation processes.

scholarly journals Chemical insights, explicit chemistry, and yields of secondary organic aerosol from OH radical oxidation of methylglyoxal and glyoxal in the aqueous phase

2013 ◽  
Vol 13 (17) ◽  
pp. 8651-8667 ◽  
Author(s):  
Y. B. Lim ◽  
Y. Tan ◽  
B. J. Turpin
Keyword(s):  
Acetic Acid ◽  
Aqueous Phase ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Oxidation Products ◽  
Radical Reactions ◽  
Organic Radical ◽  
Oh Radical ◽  
Radical Oxidation

Abstract. Atmospherically abundant, volatile water-soluble organic compounds formed through gas-phase chemistry (e.g., glyoxal (C2), methylglyoxal (C3), and acetic acid) have great potential to form secondary organic aerosol (SOA) via aqueous chemistry in clouds, fogs, and wet aerosols. This paper (1) provides chemical insights into aqueous-phase OH-radical-initiated reactions leading to SOA formation from methylglyoxal and (2) uses this and a previously published glyoxal mechanism (Lim et al., 2010) to provide SOA yields for use in chemical transport models. Detailed reaction mechanisms including peroxy radical chemistry and a full kinetic model for aqueous photochemistry of acetic acid and methylglyoxal are developed and validated by comparing simulations with the experimental results from previous studies (Tan et al., 2010, 2012). This new methylglyoxal model is then combined with the previous glyoxal model (Lim et al., 2010), and is used to simulate the profiles of products and to estimate SOA yields. At cloud-relevant concentrations (~ 10−6 − ~ 10−3 M; Munger et al., 1995) of glyoxal and methylglyoxal, the major photooxidation products are oxalic acid and pyruvic acid, and simulated SOA yields (by mass) are ~ 120% for glyoxal and ~ 80% for methylglyoxal. During droplet evaporation oligomerization of unreacted methylglyoxal/glyoxal that did not undergo aqueous photooxidation could enhance yields. In wet aerosols, where total dissolved organics are present at much higher concentrations (~ 10 M), the major oxidation products are oligomers formed via organic radical–radical reactions, and simulated SOA yields (by mass) are ~ 90% for both glyoxal and methylglyoxal. Non-radical reactions (e.g., with ammonium) could enhance yields.

scholarly journals A dynamic plant chamber system with downstream reaction chamber to study the effects of pollution on biogenic emissions

2013 ◽  
Vol 6 (5) ◽  
pp. 9005-9036
Author(s):  
J. Timkovsky ◽  
P. Gankema ◽  
R. Pierik ◽  
R. Holzinger
Keyword(s):  
Degradation Products ◽  
Proton Transfer Reaction ◽  
Reaction Chamber ◽  
Oxidation Products ◽  
Chemical Degradation ◽  
Biogenic Emissions ◽  
Dynamic Plant ◽  
Cryogenic Trapping ◽  
Plant Emissions ◽  
Set Up

Abstract. A system of two dynamic plant chambers and a downstream reaction chamber has been set up to investigate the emission of biogenic volatile organic compounds (BVOC) and possible effects from pollutants such as ozone. The system can be used to compare BVOC emissions from two sets of differently treated plants, or to study the photochemistry of real plant emissions under polluted conditions without exposing the plants to pollutants. The main analytical tool is a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) which allows online monitoring of biogenic emissions and chemical degradation products. The identification of BVOCs and their oxidation products is aided by cryogenic trapping and subsequent in situ gas chromatographic analysis. The data presented in the paper demonstrates the good performance of the setup.

scholarly journals Current estimates of biogenic emissions from Eucalypts uncertain for Southeast Australia

2016 ◽  
Author(s):  
K. M. Emmerson ◽  
I. E. Galbally ◽  
A. B. Guenther ◽  
C. Paton-Walsh ◽  
E.-A. Guerette ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Species ◽  
Field Measurements ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Emission Rates ◽  
Chemical Transport Model ◽  
Southeast Australia ◽  
Unusual Position ◽  
Adult Trees

Abstract. The biogenic emissions of isoprene and monoterpenes are one of the main drivers of atmospheric photochemistry, including oxidant and secondary organic aerosol production. In this paper, the emission rates of isoprene and monoterpenes from Australian vegetation are investigated for the first time using the Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGANv2.1), the CSIRO chemical transport model, and atmospheric observations of isoprene, monoterpenes and isoprene oxidation products (methacrolein and methyl-vinyl-ketone). Observations from four field campaigns during three different seasons are used, covering urban, coastal suburban and inland forest areas. The observed concentrations of isoprene and monoterpenes were of a broadly similar magnitude, which may indicate that southeast Australia holds an unusual position where neither chemical species dominates. The model results overestimate the observed atmospheric concentrations of isoprene (up to a factor of 6) and underestimate the monoterpene concentrations (up to a factor of 4). This may occur because the emission rates currently used in MEGANv2.1 for Australia are drawn mainly from young Eucalypt trees (< 7 years), which may emit more isoprene than adult trees. There is no single increase/decrease factor for the emissions which suits all seasons and conditions studied. There is a need for further field measurements of in-situ isoprene and monoterpene emission fluxes in Australia.

scholarly journals Fragmentation vs. functionalization: chemical aging and organic aerosol formation

2011 ◽  
Vol 11 (20) ◽  
pp. 10553-10563 ◽  
Author(s):  
H. J. Chacon-Madrid ◽  
N. M. Donahue
Keyword(s):  
Organic Aerosol ◽  
Transformation Process ◽  
Oxidation Products ◽  
Oxidation States ◽  
Oh Radical ◽  
Vapor Pressures ◽  
Aerosol Formation ◽  
Chemical Aging ◽  
Carbon Backbone ◽  
Insight Into

Abstract. The transformation process that a carbon backbone undergoes in the atmosphere is complex and dynamic. Understanding all these changes for all the species in detail is impractical; however, choosing different molecules that resemble progressively higher stages of oxidation or aging and studying them can give us an insight into general characteristics and mechanisms. Here we determine secondary organic aerosol (SOA) mass yields of two sequences of molecules reacting with the OH radical at high NOx. Each sequence consists of species with similar vapor pressures, but a succession of oxidation states. The first sequence consists of n-pentadecane, n-tridecanal, 2-, 7-tridecanone, and pinonaldehyde. The second sequence consists of n-nonadecane, n-heptadecanal and cis-pinonic acid. Oxidized molecules tend to have lower relative SOA mass yields; however, oxidation state alone was not enough to predict how efficiently a molecule forms SOA. Certain functionalities are able to fragment more easily than others, and even the position of these functionalities on a molecule can have an effect. n-Alkanes tend to have the highest yields, and n-aldehydes the lowest. n-Ketones have slightly higher yields when the ketone moiety is located on the side of the molecule and not in the center. In general, oxidation products remain efficient SOA sources, though fragmentation makes them less effective than comparable alkanes.

scholarly journals Terpenes and their oxidation products in the French Landes forest: insight from Vocus PTR-TOF measurements

2019 ◽  
Author(s):  
Haiyan Li ◽  
Matthieu Riva ◽  
Pekka Rantala ◽  
Liine Heikkinen ◽  
Kaspar Daellenbach ◽  
...  
Keyword(s):  
Gas Phase ◽  
Detection Efficiency ◽  
Ambient Air ◽  
Reaction Rates ◽  
Early Morning ◽  
Oxidation Products ◽  
Atmospheric Oxidation ◽  
Organic Nitrates ◽  
Reaction Products ◽  
Wide Range

Abstract. The capabilities of the recently developed Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF) are reported for the first time based on ambient measurements. With the deployment of the Vocus PTR-TOF, we present an overview of the observed gas-phase (oxygenated) molecules in the French Landes forest during summertime 2018 and gain insights into the atmospheric oxidation of terpenes, which are emitted in large quantities in the atmosphere and play important roles in secondary organic aerosol production. Due to the greatly improved detection efficiency compared to traditional PTR instruments, the Vocus PTR-TOF identifies a large amount of gas-phase signals with elemental composition categories including CH, CHO, CHN, CHS, CHON, CHOS, and others. Multiple hydrocarbons are detected, with carbon numbers up to 20. Particularly, we report the first direct observations of low-volatility diterpenes in the ambient air. The diurnal cycle of diterpenes is similar to that of monoterpenes and sesquiterpenes, but contrary to that of isoprene. Various types of terpene reaction products and intermediates are also characterized. Generally, the more oxidized products from terpene oxidations show a broad peak in the day due to the strong photochemical effects, while the less oxygenated products peak in the early morning and/or in the evening. To evaluate the importance of different formation pathways in terpene chemistry, the reaction rates of terpenes with main oxidants (i.e., hydroxyl radical, OH; ozone, O3; and nitrate radical, NO3) are calculated. For the less oxidized non-nitrate monoterpene oxidation products, their morning peaks likely have contributions from both O3- and OH-initiated monoterpene oxidation. Due to the decreased OH concentration at night, monoterpene ozonolysis becomes more important in the evening. For the monoterpene-derived organic nitrates, oxidations by O3, OH, and NO3 radicals all contribute to their formation, with their relative roles varying considerably over the course of the day. Through a detailed analysis of terpene chemistry, this study demonstrates the capability of the Vocus PTR-TOF in the detection of a wide range of oxidized reaction products in ambient and remote conditions, which highlights its importance in investigating atmospheric oxidation processes.

scholarly journals Chemistry of new particle growth in mixed urban and biogenic emissions – insights from CARES

2014 ◽  
Vol 14 (2) ◽  
pp. 2043-2085 ◽  
Author(s):  
A. Setyan ◽  
C. Song ◽  
M. Merkel ◽  
W. B. Knighton ◽  
T. B. Onasch ◽  
...  
Keyword(s):  
Sierra Nevada ◽  
Bulk Composition ◽  
Particle Growth ◽  
Climate Impacts ◽  
Oxidation Products ◽  
Rural Site ◽  
Urban Site ◽  
Biogenic Emissions ◽  
Urban Plumes ◽  
New Particles

Abstract. Regional new particle formation and growth events (NPE) were observed on most days over the Sacramento and western Sierra Foothills area of California in June 2010 during the Carbonaceous Aerosols and Radiative Effect Study (CARES). Simultaneous particle measurements at both the T0 (Sacramento, urban site) and the T1 (Cool, rural site located ~40 km northeast of Sacramento) sites of CARES indicate that the NPE usually occurred in the morning with the appearance of an ultrafine mode centered at ~15 nm (in mobility diameter, Dm, measured by a scanning mobility particle sizer operating in the range 10–858 nm) followed by the growth of this mode to ~50 nm in the afternoon. These events were generally associated with southwesterly winds bringing urban plumes from Sacramento to the T1 site. The growth rate was on average higher at T0 (7.1 ± 2.7 nm h−1) than at T1 (6.2 ± 2.5 nm h−1), likely due to stronger anthropogenic influences at T0. Using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), we investigated the evolution of the size-resolved chemical composition of new particles at T1. Our results indicate that the growth of new particles was driven primarily by the condensation of oxygenated organic species and, to a lesser extent, ammonium sulfate. New particles appear to be fully neutralized during growth, consistent with high NH3 concentration in the region. Nitrogen-containing organic ions (i.e., CHN+, CH4N+, C2H3N+, and C2H4N+) that are indicative of the presence of alkyl-amine species in submicrometer particles enhanced significantly during the NPE days, suggesting that amines might have played a role in these events. Our results also indicate that the bulk composition of the ultrafine mode organics during NPE was very similar to that of anthropogenically-influenced secondary organic aerosol (SOA) observed in transported urban plumes. In addition, the concentrations of species representative of urban emissions (e.g., black carbon, CO, NOx, and toluene) were significantly higher whereas the photo-oxidation products of biogenic VOC and the biogenically-influenced SOA also increased moderately during the NPE days compared to the non-event days. These results indicate that the frequently occurring NPE over the Sacramento and Sierra Nevada regions were mainly driven by urban plumes from Sacramento and that the interaction of regional biogenic emissions with the urban plumes has enhanced the new particle growth. This finding has important implication for quantifying the climate impacts of NPE on global scale.

scholarly journals Evidence for an unidentified non-photochemical ground-level source of formaldehyde in the Po Valley with potential implications for ozone production

2015 ◽  
Vol 15 (3) ◽  
pp. 1289-1298 ◽  
Author(s):  
J. Kaiser ◽  
G. M. Wolfe ◽  
B. Bohn ◽  
S. Broch ◽  
H. Fuchs ◽  
...  
Keyword(s):  
Agricultural Land ◽  
Ground Level ◽  
Early Morning ◽  
Oxidation Products ◽  
Ozone Production ◽  
Model Calculations ◽  
Po Valley ◽  
International Regulations ◽  
Convective Mixed Layer ◽  
D Model

Abstract. Ozone concentrations in the Po Valley of northern Italy often exceed international regulations. As both a source of radicals and an intermediate in the oxidation of most volatile organic compounds (VOCs), formaldehyde (HCHO) is a useful tracer for the oxidative processing of hydrocarbons that leads to ozone production. We investigate the sources of HCHO in the Po Valley using vertical profile measurements acquired from the airship Zeppelin NT over an agricultural region during the PEGASOS 2012 campaign. Using a 1-D model, the total VOC oxidation rate is examined and discussed in the context of formaldehyde and ozone production in the early morning. While model and measurement discrepancies in OH reactivity are small (on average 3.4 ± 13%), HCHO concentrations are underestimated by as much as 1.5 ppb (45%) in the convective mixed layer. A similar underestimate in HCHO was seen in the 2002–2003 FORMAT Po Valley measurements, though the additional source of HCHO was not identified. Oxidation of unmeasured VOC precursors cannot explain the missing HCHO source, as measured OH reactivity is explained by measured VOCs and their calculated oxidation products. We conclude that local direct emissions from agricultural land are the most likely source of missing HCHO. Model calculations demonstrate that radicals from degradation of this non-photochemical HCHO source increase model ozone production rates by as much as 0.6 ppb h−1 (12%) before noon.

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