scholarly journals Measurements of the OH radical yield from the ozonolysis of biogenic alkenes: A potential interference with laser-induced fluorescence measurements of ambient OH

2017 ◽  
Author(s):  
Pamela Rickly ◽  
Philip S. Stevens
Keyword(s):  
Flow Reactor ◽  
Laser Induced Fluorescence ◽  
Fluorescence Measurements ◽  
Criegee Intermediates ◽  
Volatile Organic ◽  
Forested Areas ◽  
Rigorous Test ◽  
Reactor Operating ◽  
Gas Expansion ◽  
Radical Yield

Abstract. Reactions of the hydroxyl radical (OH) play a central role in the chemistry of the atmosphere, and measurements of its concentration can provide a rigorous test of our understanding of atmospheric oxidation. Several recent studies have shown large discrepancies between measured and modeled OH concentrations in forested areas impacted by emissions of biogenic volatile organic compounds (BVOCs), where modeled concentrations were significantly lower than measurements. A potential reason for some of these discrepancies involves interferences associated with the measurement of OH using the Laser-Induced Fluorescence – Fluorescence Assay with Gas Expansion (LIF-FAGE) technique in these environments. In this study, a turbulent flow reactor operating at atmospheric pressure was coupled to a LIF-FAGE cell and the OH signal produced from the ozonolysis of several BVOCs was measured. To distinguish between OH produced from the ozonolysis reactions and any OH artefact produced inside the LIF-FAGE cell, an external chemical scrubbing technique was used, allowing for the direct measurement of any interference. An interference under high ozone and BVOC concentrations was observed that was not laser generated and was independent of the ozonolysis reaction time. Addition of acetic acid to the reactor eliminated the interference, suggesting that the source of the interference in these experiments involved the decomposition of stabilized Criegee intermediates inside the FAGE detection cell.

scholarly journals Measurements of a potential interference with laser-induced fluorescence measurements of ambient OH from the ozonolysis of biogenic alkenes

2018 ◽  
Vol 11 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Pamela Rickly ◽  
Philip S. Stevens
Keyword(s):  
Flow Reactor ◽  
Laser Induced Fluorescence ◽  
Fluorescence Measurements ◽  
Criegee Intermediates ◽  
Volatile Organic ◽  
Forested Areas ◽  
Ambient Concentrations ◽  
Rigorous Test ◽  
Reactor Operating ◽  
Gas Expansion

Abstract. Reactions of the hydroxyl radical (OH) play a central role in the chemistry of the atmosphere, and measurements of its concentration can provide a rigorous test of our understanding of atmospheric oxidation. Several recent studies have shown large discrepancies between measured and modeled OH concentrations in forested areas impacted by emissions of biogenic volatile organic compounds (BVOCs), where modeled concentrations were significantly lower than measurements. A potential reason for some of these discrepancies involves interferences associated with the measurement of OH using the laser-induced fluorescence–fluorescence assay by gas expansion (LIF-FAGE) technique in these environments. In this study, a turbulent flow reactor operating at atmospheric pressure was coupled to a LIF-FAGE cell and the OH signal produced from the ozonolysis of α-pinene, β-pinene, ocimene, isoprene, and 2-methyl-3-buten-2-ol (MBO) was measured. To distinguish between OH produced from the ozonolysis reactions and any OH artifact produced inside the LIF-FAGE cell, an external chemical scrubbing technique was used, allowing for the direct measurement of any interference. An interference under high ozone (between 2 × 1013 and 10 × 1013 cm−3) and BVOC concentrations (between approximately 0.1 × 1012 and 40 × 1012 cm−3) was observed that was not laser generated and was independent of the ozonolysis reaction time. For the ozonolysis of α- and β-pinene, the observed interference accounted for approximately 40 % of the total OH signal, while for the ozonolysis of ocimene the observed interference accounted for approximately 70 % of the total OH signal. Addition of acetic acid to the reactor eliminated the interference, suggesting that the source of the interference in these experiments involved the decomposition of stabilized Criegee intermediates (SCIs) inside the FAGE detection cell. Extrapolation of these measurements to ambient concentrations suggests that these interferences should be below the detection limit of the instrument.

scholarly journals Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

2018 ◽  
Vol 11 (1) ◽  
pp. 95-109 ◽  
Author(s):  
Michelle M. Lew ◽  
Sebastien Dusanter ◽  
Philip S. Stevens
Keyword(s):  
Laser Induced Fluorescence ◽  
Biogenic Emissions ◽  
Peroxy Radicals ◽  
Indiana University ◽  
Hydroperoxy Radical ◽  
Volatile Organic ◽  
Field Campaigns ◽  
Gas Expansion ◽  
The Impact ◽  
Ho2 Radical

Abstract. One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2-to-HO2 conversion for the Indiana University laser-induced fluorescence–fluorescence assay by gas expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds (VOCs) with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene-derived RO2 radicals and 20 % of alkane-derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign (MCMA-2006), where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene.

scholarly journals Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

2017 ◽  
Author(s):  
Michelle M. Lew ◽  
Sebastien Dusanter ◽  
Philip S. Stevens
Keyword(s):  
Laser Induced Fluorescence ◽  
Biogenic Emissions ◽  
Peroxy Radicals ◽  
Indiana University ◽  
Hydroperoxy Radical ◽  
Volatile Organic ◽  
Field Campaigns ◽  
Gas Expansion ◽  
The Impact ◽  
Ho2 Radical

Abstract. One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2 to HO2 conversion for the Indiana University Laser-Induced Fluorescence – Fluorescence Assay by Gas Expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene derived RO2 radicals and 20 % of alkane derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign, where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene.

scholarly journals Insights into hydroxyl measurements and atmospheric oxidation in a California forest

2012 ◽  
Vol 12 (17) ◽  
pp. 8009-8020 ◽  
Author(s):  
J. Mao ◽  
X. Ren ◽  
L. Zhang ◽  
D. M. Van Duin ◽  
R. C. Cohen ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Traditional Method ◽  
Laser Induced Fluorescence ◽  
New Method ◽  
Biogenic Volatile Organic Compounds ◽  
Temperature Dependent ◽  
Volatile Organic ◽  
Penn State ◽  
Oxidation Chemistry ◽  
Gas Expansion

Abstract. The understanding of oxidation in forest atmospheres is being challenged by measurements of unexpectedly large amounts of hydroxyl (OH). A significant number of these OH measurements were made by laser-induced fluorescence in low-pressure detection chambers (called Fluorescence Assay with Gas Expansion (FAGE)) using the Penn State Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS). We deployed a new chemical removal method to measure OH in parallel with the traditional FAGE method in a California forest. The new method gives on average only 40–60% of the OH from the traditional method and this discrepancy is temperature dependent. Evidence indicates that the new method measures atmospheric OH while the traditional method is affected by internally generated OH, possibly from oxidation of biogenic volatile organic compounds. The improved agreement between OH measured by this new technique and modeled OH suggests that oxidation chemistry in at least one forest atmosphere is better understood than previously thought.

scholarly journals Insights into hydroxyl measurements and atmospheric oxidation in a California forest

2012 ◽  
Vol 12 (3) ◽  
pp. 6715-6744 ◽  
Author(s):  
J. Mao ◽  
X. Ren ◽  
W. H. Brune ◽  
D. M. Van Duin ◽  
R. C. Cohen ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Traditional Method ◽  
Laser Induced Fluorescence ◽  
New Method ◽  
Biogenic Volatile Organic Compounds ◽  
Temperature Dependent ◽  
Volatile Organic ◽  
Penn State ◽  
Oxidation Chemistry ◽  
Gas Expansion

Abstract. The understanding of oxidation in forest atmospheres is being challenged by measurements of unexpectedly large amounts of hydroxyl (OH). A significant number of these OH measurements were made by laser-induced fluorescence in low-pressure detection chambers (called Fluorescence Assay with Gas Expansion (FAGE)) using the Penn State Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS). We deployed a new chemical removal method to measure OH in parallel with the traditional FAGE method. The new method gives on average only 40–50% of the OH from the traditional method and this discrepancy is temperature-dependent. Evidence indicates that the new method measures atmospheric OH while the traditional method is affected by internally generated OH, possibly from oxidation of biogenic volatile organic compounds. The agreement between OH measured by this new technique and modeled OH suggests that oxidation chemistry in at least one forest atmosphere is better understood than previously thought.

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