In situ measurement for tropospheric OH radical by Laser Induced Fluorescence technique during STORM campaign

2020 ◽  
Author(s):  
Fengyang Wang ◽  
Renzhi Hu ◽  
Pinhua Xie ◽  
Yihui Wang ◽  
Shengrong Lou ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Photon Counting ◽  
Ambient Air ◽  
Laser Induced Fluorescence ◽  
Detection Sensitivity ◽  
Oh Radical ◽  
Fluorescence Technique ◽  
Radical Concentration ◽  
Mobile Observation

<p>Hydroxyl (OH) play an essential role in atmospheric chemistry. OH radical is an indicator of atmospheric oxidation and self-purification, which determines the removal of most trace gases in the atmosphere, such as CO, SO<sub>2</sub>, NO<sub>2</sub>, CH<sub>4</sub> and other volatile organic compounds (VOCs). A ground-based system for measurement of tropospheric OH radical by Laser Induced Fluorescence technique (AIOFM-LIF) was developed and integrated into a mobile observation platform for field observation. Ambient air expands through a 0.4 mm nozzle to low pressure. OH radical is irradiated by the 308 nm laser pulse at a repetition rate of 8.5 kHz, accompanying the release fluorescence of the A<sup>2</sup>Σ<sup>+</sup>(v’=0)—X<sup>2</sup>Π<sub>i</sub>(v’’=0) transition at 308 nm with the resultant fluorescence being detected by gated photon counting. The detection sensitivity of AIOFM-LIF system was calibrated by a portable standard OH radical source based on water photolysis-ozone actinometry. Following laboratory and field calibrations to characterise the instrument sensitivity, OH radical detection limits were (1.84±0.26) × 10<sup>5</sup> cm<sup>-3</sup> and (3.69±0.52) × 10<sup>5</sup> cm<sup>-3</sup> at night and noon, respectively. During “A comprehensive STudy of the Ozone foRmation Mechanism in Shenzhen” (STORM) campaign, AIOFM-LIF system was deployed in Shenzhen, China, and OH radical concentration was obtained validly except for the rainy days. Mean diurnal variation of HOx radical concentration was obtained, and the peak was 6.6×10<sup>6</sup> cm<sup>-3</sup> which appeared around 12:00 at noon. A general good agreement of OH radical concentration with j(O<sup>1</sup>D) was observed with a high correlation (R<sup>2</sup> =0.77), which illustrates that photolysis of ozone is an important source of OH radical during this campaign. A box model was applied to simulate the concentrations of OH at this field site, the primary production of OH radical was generally dominated by photolysis of O<sub>3</sub>, HONO, HCHO, while the other production was contributed by calculated species (OVOCs).</p>

Single-Molecule Detection by Laser-Induced Fluorescence Technique with a Position-Sensitive Photon-Counting Apparatus

1994 ◽  
Vol 33 (Part 1, No. 3A) ◽  
pp. 1571-1576 ◽  
Author(s):  
Mitsuru Ishikawa ◽  
Ken-ichi Hirano ◽  
Tsuyoshi Hayakawa ◽  
Shigeru Hosoi ◽  
Sydney Brenner
Keyword(s):  
Single Molecule ◽  
Photon Counting ◽  
Laser Induced Fluorescence ◽  
Single Molecule Detection ◽  
Fluorescence Technique ◽  
Position Sensitive

scholarly journals Implementation of a chemical background method for atmospheric OH measurements by laser-induced fluorescence: characterisation and observations from the UK and China

2020 ◽  
Vol 13 (6) ◽  
pp. 3119-3146 ◽  
Author(s):  
Robert Woodward-Massey ◽  
Eloise J. Slater ◽  
Jake Alen ◽  
Trevor Ingham ◽  
Danny R. Cryer ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Ambient Air ◽  
Laser Induced Fluorescence ◽  
Excitation Wavelength ◽  
Atmospheric Conditions ◽  
Wide Range ◽  
Model Predictions ◽  
The Difference ◽  
The Uk ◽  
Interference Tests

Abstract. Hydroxyl (OH) and hydroperoxy (HO2) radicals are central to the understanding of atmospheric chemistry. Owing to their short lifetimes, these species are frequently used to test the accuracy of model predictions and their underlying chemical mechanisms. In forested environments, laser-induced fluorescence–fluorescence assay by gas expansion (LIF–FAGE) measurements of OH have often shown substantial disagreement with model predictions, suggesting the presence of unknown OH sources in such environments. However, it is also possible that the measurements have been affected by instrumental artefacts, due to the presence of interfering species that cannot be discriminated using the traditional method of obtaining background signals via modulation of the laser excitation wavelength (“OHwave”). The interference hypothesis can be tested by using an alternative method to determine the OH background signal, via the addition of a chemical scavenger prior to sampling of ambient air (“OHchem”). In this work, the Leeds FAGE instrument was modified to include such a system to facilitate measurements of OHchem, in which propane was used to selectively remove OH from ambient air using an inlet pre-injector (IPI). The IPI system was characterised in detail, and it was found that the system did not reduce the instrument sensitivity towards OH (< 5 % difference to conventional sampling) and was able to efficiently scavenge external OH (> 99 %) without the removal of OH formed inside the fluorescence cell (< 5 %). Tests of the photolytic interference from ozone in the presence of water vapour revealed a small but potentially significant interference, equivalent to an OH concentration of ∼4×105 molec. cm−3 under typical atmospheric conditions of [O3] =50 ppbv and [H2O] =1 %. Laboratory experiments to investigate potential interferences from products of isoprene ozonolysis did result in interference signals, but these were negligible when extrapolated down to ambient ozone and isoprene levels. The interference from NO3 radicals was also tested but was found to be insignificant in our system. The Leeds IPI module was deployed during three separate field intensives that took place in summer at a coastal site in the UK and both in summer and winter in the megacity of Beijing, China, allowing for investigations of ambient OH interferences under a wide range of chemical and meteorological conditions. Comparisons of ambient OHchem measurements to the traditional OHwave method showed excellent agreement, with OHwave vs OHchem slopes of 1.05–1.16 and identical behaviour on a diel basis, consistent with laboratory interference tests. The difference between OHwave and OHchem (“OHint”) was found to scale non-linearly with OHchem, resulting in an upper limit interference of (5.0±1.4) ×106 molec. cm−3 at the very highest OHchem concentrations measured (23×106 molec. cm−3), accounting for ∼14 %–21 % of the total OHwave signal.

OH reactivity in three major city clusters of China in ozone seasons: insights for regional ozone formation

2020 ◽  
Author(s):  
Shengrong Lou ◽  
Xiangsen Shen ◽  
Xin Li ◽  
Qian Wang ◽  
Shuoying Liu
Keyword(s):  
Control Strategies ◽  
Ambient Air ◽  
Ozone Production ◽  
Trace Gas ◽  
Ozone Formation ◽  
Oh Radical ◽  
Ozone Pollution ◽  
Major City ◽  
Photochemical Process

&lt;p&gt;&lt;span&gt;OH radical is the key driver of the photochemical process and closely related to ozone formation. OH reactivity is the quantification of OH radical sink in ambient air. In this study, in-situ OH reactivity measurements are carried out in Shenzhen, Chengdu and Changzhou, three typical cities in major city clusters of China, during their ozone pollution seasons. The measured OH reactivity is ranging from 5~35 s-1 under various meteorological conditions and trace gas concentrations. Aldehydes such as HCHO and acetaldehyde, mainly from the secondary formation of VOCs, are the principal contributors at day time. Primary VOCs such as toluene and biogenic VOCs such as isoprene play different roles in three measurement locations. The missing OH reactivity, which is defined as the OH reactivity that cannot be explained by trace gas measurements, are evaluated by in-situ measurement results as well as an observation-based model. Gas-phase secondary pollutants could be the main source of the missing OH reactivity. The sensitivity tests by the OBM model show ozone production in all areas is mainly VOC-limited but the key precursors of ozone are not identical, leading to different control strategies.&lt;/span&gt;&lt;/p&gt;

scholarly journals Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

2020 ◽  
Author(s):  
Changmin Cho ◽  
Andreas Hofzumahaus ◽  
Hendrik Fuchs ◽  
Hans-Peter Dorn ◽  
Marvin Glowania ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Trace Gases ◽  
Ambient Air ◽  
Laser Induced Fluorescence ◽  
Optical Absorption Spectroscopy ◽  
Oh Radicals ◽  
Atmospheric Conditions ◽  
Atmospheric Measurements ◽  
Chemical Modulation ◽  
Scavenging Efficiency

Abstract. Precise and accurate hydroxyl radical (OH) measurements are essential to investigate how trace gases are oxidized and transformed in the troposphere and how secondary pollutants like ozone (O3) are formed. Laser induced fluorescence (LIF) is a widely used technique for the measurement of ambient OH radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell. In this study, we describe the application, characterization, and validation of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the atmospheric simulation chamber SAPHIR. Besides dedicated experiments in synthetic air, the new technique was extensively tested during the year-round Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. It allowed performing OH measurement comparisons with Differential Optical Absorption Spectroscopy (DOAS) and investigation of interferences in a large variety of chemical and meteorological conditions. A good agreement was obtained in the LIF DOAS intercomparison within instrumental accuracies (18 % for LIF, 6.5 % for DOAS) which confirms that the new chemical modulation system of the FZJ-LIF instrument is suitable for measurement of interference-free OH concentrations. Known interferences from O3 + H2O and the nitrate radical (NO3) were quantified with the CMR in synthetic air in the chamber and found to be 3.0 × 105 cm-3 and 0.6 × 105 cm-3, respectively, for typical ambient air condition (O3 = 50 ppbv, H2O = 1 %, NO3 = 10 pptv). The interferences measured in ambient air during the JULIAC campaign in summer season had the median diurnal variation of the interference with a maximum daytime value of 0.9 × 106 cm-3 and a minimum nighttime value of 0.4 × 106 cm-3. The highest interference of 2 × 106 cm-3 occurred in a heat wave from 22–29 August, when the air temperature and ozone increased to 40 °C and 100 ppbv, respectively. All observed interferences could be fully explained by the known O3 + H2O interference, which is routinely corrected in FZJ-LIF measurements when no chemical modulation is applied. No evidence for unexplained interference was found during the JULIAC campaign. A kinetic chemical model of the chemical modulation reactor was developed and applied to estimate the possible perturbation of the OH transmission and scavenging efficiency by reactive atmospheric trace gases. These can remove OH by gas phase reactions in the reactor, or produce OH by non-photolytical reactions, most importantly by the reaction of ambient HO2 with NO. The interfering processes become relevant at high atmospheric OH reactivities. For the conditions of the JULIAC campaign with OH reactivities below 20 s-1, the influence on the determination of ambient OH concentrations was small (on average: 2 %). However, in environments with high OH reactivities, such as in a rain forest or megacity, the expected perturbation in the currently used chemical modulation reactor could be large (more than a factor of 2) and would need careful analysis and correction. This implies that chemical modulation, which was developed to eliminate interferences in ambient OH measurements, itself can be subject to interferences that depend on ambient atmospheric conditions.

scholarly journals Chemical composition of pre-monsoon air in the Indo-Gangetic Plain measured using a new air quality facility and PTR-MS: high surface ozone and strong influence of biomass burning

2014 ◽  
Vol 14 (12) ◽  
pp. 5921-5941 ◽  
Author(s):  
V. Sinha ◽  
V. Kumar ◽  
C. Sarkar
Keyword(s):  
Air Quality ◽  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Air Pollutants ◽  
Surface Ozone ◽  
Ambient Air ◽  
Ambient Air Quality ◽  
Gangetic Plain ◽  
Indo Gangetic Plain

Abstract. One seventh of the world's population lives in the Indo-Gangetic Plain (IGP) and the fertile region sustains agricultural food crop production for much of South Asia, yet it remains one of the most under-studied regions of the world in terms of atmospheric composition and chemistry. In particular, the emissions and chemistry of volatile organic compounds (VOCs) that form surface ozone and secondary organic aerosol through photochemical reactions involving nitrogen oxides are not well understood. In this study, ambient levels of VOCs such as methanol, acetone, acetaldehyde, acetonitrile and isoprene were measured for the first time in the IGP. A new atmospheric chemistry facility that combines India's first high-sensitivity proton transfer reaction mass spectrometer, an ambient air quality station and a meteorological station, was used to quantify in situ levels of several VOCs and air pollutants in May 2012 at a suburban site in Mohali (northwest IGP). Westerly winds arriving at high wind speeds (5–20 m s−1) in the pre-monsoon season at the site were conducive for chemical characterization of regional emission signatures. Average levels of VOCs and air pollutants in May~2012 ranged from 1.2 to 2.7 nmol mol−1 for aromatic VOCs, 5.9 to 37.5 nmol mol−1 for the oxygenated VOCs, 1.4 nmol mol−1 for acetonitrile, 1.9 nmol mol−1 for isoprene, 567 nmol mol−1 for carbon monoxide, 57.8 nmol mol−1 for ozone, 11.5 nmol mol−1 for nitrogen oxides, 7.3 nmol mol−1 for sulfur dioxide, 104 μg m−3 for PM2.5 and 276 μg m−3 for PM10. By analyzing the one-minute in situ data with meteorological parameters and applying chemical tracers (e.g., acetonitrile for biomass burning) and inter-VOC correlations, we were able to constrain major emission source activities on both temporal and diel scales. Wheat residue burning caused massive increases (> 3 times the baseline values) for all the measured VOCs and primary pollutants. Other forms of biomass burning at night were also a significant source of oxygenated VOCs and isoprene (r2 with acetonitrile &amp;geq;0.5 for nighttime data), which is remarkable in terms of atmospheric chemistry implications. Surface ozone exceeded the 8 h national ambient air quality limit of 100 μg O3 m−3 (~50 ppbv) on a daily basis, except for 17 May 2012, when a severe dust storm event (PM2.5 > 800 μg m−3; PM10 > 2700 μg m−3) characterized by long-range transport from the west impacted the site. The novel data set and results point to the occurrence of high primary emissions of reactive VOCs. They also highlight the urgent need for establishing more comprehensive observational facilities in the IGP to constrain the spatial and seasonal variability of atmospheric chemical constituents. Such efforts will enable a mechanistic-level understanding of the in situ chemical processes controlling the formation of surface ozone, a necessary step for effective ozone mitigation and improvement of the regional air quality.

scholarly journals A Sensor Array Realized by a Single Flexible TiO2/POMs Film to Contactless Detection of Triacetone Triperoxide

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 915 ◽  
Author(s):  
Xiaorong Lü ◽  
Puqi Hao ◽  
Guanshun Xie ◽  
Junyuan Duan ◽  
Bingxin Liu
Keyword(s):  
Sensor Array ◽  
Sensor Arrays ◽  
Ambient Air ◽  
Detection Sensitivity ◽  
Excitation Wavelength ◽  
Triacetone Triperoxide ◽  
Sensor Film ◽  
Vapor Sensor ◽  
The Stability

The homemade explosive, triacetone triperoxide (TATP), is easy to synthesize, sensitive to detonation but hard to detect directly. Vapor sensor arrays composed of a few sensor materials have the potential to discriminate TATP, but the stability of the sensor array is always a tricky problem since each sensor may encounter a device fault. Thus, a sensor array based on a single optoelectronic TiO2/PW11 sensor was first constructed by regulating the excitation wavelength to discriminate TATP from other explosives. By in situ doping of Na3PW12O40, a Keggin structure of PW11 formed on the TiO2 to promote the photoinduced electron-hole separation, thus obviously improving the detection sensitivity of the sensor film and shortening the response time. The response of the TiO2/PW11 sensor film to TATP under 365, 450 and 550 nm illumination is 81%, 42%, and 37%, respectively. The TiO2/PW11 sensor features selectivity to TATP and is able to detect less than 50 ppb. The flexibility and stability of the flexible sensor film is also demonstrated with the extent of bending. Furthermore, the sensing response cannot be affected by ambient air below 60% relative humidity.

scholarly journals Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

2021 ◽  
Vol 14 (3) ◽  
pp. 1851-1877
Author(s):  
Changmin Cho ◽  
Andreas Hofzumahaus ◽  
Hendrik Fuchs ◽  
Hans-Peter Dorn ◽  
Marvin Glowania ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Trace Gases ◽  
Ambient Air ◽  
Laser Induced Fluorescence ◽  
Optical Absorption Spectroscopy ◽  
Oh Radicals ◽  
Atmospheric Measurements ◽  
Chemical Modulation ◽  
Scavenging Efficiency

Abstract. Precise and accurate hydroxyl radical (OH) measurements are essential to investigate mechanisms for oxidation and transformation of trace gases and processes leading to the formation of secondary pollutants like ozone (O3) in the troposphere. Laser-induced fluorescence (LIF) is a widely used technique for the measurement of ambient OH radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell (Mao et al., 2012; Novelli et al., 2014a). In this study, we describe the application and characterization of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber). Besides dedicated experiments in synthetic air, the new technique was extensively tested during the year-round Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. It allowed for performing OH measurement comparisons with differential optical absorption spectroscopy (DOAS) and investigation of interferences in a large variety of chemical and meteorological conditions. Good agreement was obtained in the LIF–DOAS intercomparison within instrumental accuracies (18 % for LIF and 6.5 % for DOAS) which confirms that the new chemical modulation system of the FZJ-LIF instrument is suitable for measurement of interference-free OH concentrations under the conditions of the JULIAC campaign (rural environment). Known interferences from O3+H2O and the nitrate radical (NO3) were quantified with the CMR in synthetic air in the chamber and found to be 3.0×105 and 0.6×105 cm−3, respectively, for typical ambient-air conditions (O3=50 ppbv, H2O = 1 % and NO3=10 pptv). The interferences measured in ambient air during the JULIAC campaign in the summer season showed a median diurnal variation with a median maximum value of 0.9×106 cm−3 during daytime and a median minimum value of 0.4×106 cm−3 at night. The highest interference of 2×106 cm−3 occurred in a heat wave from 22 to 29 August, when the air temperature and ozone increased to 40 ∘C and 100 ppbv, respectively. All observed interferences could be fully explained by the known O3+H2O interference, which is routinely corrected in FZJ-LIF measurements when no chemical modulation is applied. No evidence for an unexplained interference was found during the JULIAC campaign. A chemical model of the CMR was developed and applied to estimate the possible perturbation of the OH transmission and scavenging efficiency by reactive atmospheric trace gases. These can remove OH by gas phase reactions in the CMR or produce OH by non-photolytic reactions, most importantly by the reaction of ambient HO2 with NO. The interfering processes become relevant at high atmospheric OH reactivities. For the conditions of the JULIAC campaign with OH reactivities below 20 s−1, the influence on the determination of ambient OH concentrations was small (on average: 2 %). However, in environments with high OH reactivities, such as in a rain forest or megacity, the expected perturbation in the currently used chemical modulation reactor could be large (more than a factor of 2). Such perturbations need to be carefully investigated and corrected for the proper evaluation of OH concentrations when applying chemical scavenging. This implies that chemical modulation, which was developed to eliminate interferences in ambient OH measurements, itself can be subject to interferences that depend on ambient atmospheric conditions.

scholarly journals Spatially resolved measurement of hydroxyl (OH) radical concentration in a microwave plasma jet by planar laser-induced fluorescence

2014 ◽  
Vol 13 (1) ◽  
Author(s):  
Jan Voráč ◽  
Jaroslav Hnilica ◽  
Vít Kudrle ◽  
Pavel Dvořák
Keyword(s):  
Microwave Plasma ◽  
Plasma Jet ◽  
Laser Induced Fluorescence ◽  
Oh Radicals ◽  
Oh Radical ◽  
Maximal Concentration ◽  
Spatially Resolved ◽  
Radical Concentration ◽  
Planar Laser Induced Fluorescence ◽  
Planar Laser

AbstractThe spatially resolved concentration of OH radicals in the effluent of a microwave (MW) surfatron plasma jet was measured by planar laser-induced fluorescence. Two cases were compared – constant MW power and MW power modulated by 80 Hz. In both cases the maximal concentration was at the tip of the visible discharge, but for constant MW power the OH was spread over a larger volume. The maximum concentration in both cases was on the order of 10

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