Photochemistry of the Troposphere

Levy, H.

doi:10.1002/9780470133392.ch5

Cited by 70 publications

(7 citation statements)

References 187 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…0.5 ppm in the northern hemisphere, and 0.52 ppm in the southern (Simmonds et al, ). These concentrations reflect the balance of major sources of hydrogen, namely biomass burning and photolytic oxidation of hydrocarbons such as methane and isoprene in the atmosphere (Levy, ; Novelli et al, ), and sinks – oxidation by OH in the atmosphere, and bacterial consumption in soils which is weighted toward the northern hemisphere (Levy, ; Rhee et al, ). Coupled with the low aqueous solubility of hydrogen, the low atmospheric abundance leads to a low and easily calculated equilibrium concentration in surface waters.…”

Section: Introductionmentioning

confidence: 99%

On the Relationship Between Hydrogen Saturation in the Tropical Atlantic Ocean and Nitrogen Fixation by the Symbiotic Diazotroph UCYN‐A

et al. 2018

View full text Add to dashboard Cite

Dissolved hydrogen measurements were made at high resolution in surface waters along a tropical north Atlantic transect between Guadeloupe and Cape Verde in 2015 (Meteor 116). Parallel water samples acquired to assess the relative abundance of the nifH gene from several types of diazotrophs, indicated that Trichodesmium and UCYN‐A were dominant in this region. We show that a high degree of correlation exists between the hydrogen saturations and UCYN‐A nifH abundance, and a weak correlation with Trichodesmium. The findings suggest that nitrogen fixation by UCYN‐A is a major contributor to hydrogen supersaturations in this region of the ocean. The ratio of hydrogen released to nitrogen fixed has not been determined for this symbiont, but the indications are that it may be high in comparison with the small number of diazotrophs for which the ratio has been measured in laboratory cultures. We speculate that this would be consistent with the diazotroph being an exosymbiont on its haptophyte host. Our high resolution measurements of hydrogen concentrations are capable of illustrating the time and space scales of inferred activity of diazotrophs in near real‐time in a way that cannot be achieved by biological sampling and rate measurements requiring incubations with 15N2. Direct measurement of high resolution spatial variability would be relatively challenging through collection and analysis of biological samples by qPCR, and extremely challenging by 15N‐uptake techniques, neither of which methods yields real‐time data. Nonetheless, determination of fixation rates still firmly depends on the established procedure of incubations in the presence of 15N2.

show abstract

Section: Introductionmentioning

confidence: 99%

On the Relationship Between Hydrogen Saturation in the Tropical Atlantic Ocean and Nitrogen Fixation by the Symbiotic Diazotroph UCYN‐A

et al. 2018

View full text Add to dashboard Cite

show abstract

“…Eisele et al, 1996;Martinez et al, 2008). Since the 1970s OH radicals are recognised to be the major oxidant in the atmosphere converting more than 90% of the volatile organic matter (Levy, 1974). Since then many attempts were made to measure OH concentrations in the troposphere by various techniques (see review by Heard and Pilling, 2003).…”

Section: Introductionmentioning

confidence: 99%

Technical Note: Formal blind intercomparison of OH measurements: results from the international campaign HOxComp

Schlosser¹,

Brauers²,

Dorn³

et al. 2009

Atmos. Chem. Phys.

104

148

View full text Add to dashboard Cite

Abstract. Hydroxyl radicals (OH) are the major oxidizing species in the troposphere. Because of their central importance, absolute measurements of their concentrations are needed to validate chemical mechanisms of atmospheric models. The extremely low and highly variable concentrations in the troposphere, however, make measurements of OH difficult. Three techniques are currently used worldwide for tropospheric observations of OH after about 30 years of technical developments: Differential Optical Laser Absorption Spectroscopy (DOAS), Laser-Induced Fluorescence Spectroscopy (LIF), and Chemical Ionisation Mass Spectrometry (CIMS). Even though many measurement campaigns with OH data were published, the question of accuracy and precision is still under discussion.Here, we report results of the first formal, blind intercomparison of these techniques. Six OH instruments (4 LIF, 1 CIMS, 1 DOAS) participated successfully in the ground-based, international HOxComp campaign carried out in Jülich, Germany, in summer 2005. Comparisons were performed for three days in ambient air (3 LIF, 1 CIMS) and for six days in the atmosphere simulation chamber SAPHIR (3 LIF, 1 DOAS). All instruments were found to measure tropospheric OH concentrations with high sensitivity and good time resolution. The pairwise correlations between different data sets were linear and yielded high correlation coefficients (r 2 =0.75−0.96). Excellent absolute agreement wasCorrespondence to: H.-P. Dorn (h.p.dorn@fz-juelich.de) observed for the instruments at the SAPHIR chamber, yielding slopes between 1.01 and 1.13 in the linear regressions. In ambient air, the slopes deviated from unity by factors of 1.06 to 1.69, which can partly be explained by the stated instrumental accuracies. In addition, sampling inhomogeneities and calibration problems have apparently contributed to the discrepancies. The absolute intercepts of the linear regressions did not exceed 0.6×10 6 cm −3 , mostly being insignificant and of minor importance for daytime observations of OH. No relevant interferences with respect to ozone, water vapour, NO x and peroxy radicals could be detected. The HOxComp campaign has demonstrated that OH can be measured reasonably well by current instruments, but also that there is still room for improvement of calibrations.

show abstract

“…The hydroxyl radical (OH) is the main daytime oxidant controlling the removal and transformation of gaseous pollutants in the atmosphere (Levy, 1974). Its high efficiency in the oxidation of trace gases is based on the effective regeneration of OH by radical chain reactions, in which nitric oxide (NO) is oxidized to nitrogen dioxide (NO 2 ), linking the OH chemistry to the formation of the tropospheric pollutant ozone (O 3 ).…”

Section: Introduction 35mentioning

confidence: 99%

Importance of isomerization reactions for the OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

Novelli¹,

Vereecken²,

Dorn³

et al. 2019

Preprint

View full text Add to dashboard Cite

Abstract. Theoretical, laboratory and chamber studies have shown fast regeneration of hydroxyl radical (OH) in the photochemistry of isoprene largely due to previously disregarded unimolecular reactions. Based on early field measurements, nearly complete regeneration was hypothesized for a wide range of tropospheric conditions, including areas such as the rainforest where slow regeneration of OH radicals is expected due to low concentrations of nitric oxide (NO). In this work the OH regeneration in the isoprene oxidation is directly quantified for the first time through experiments covering a wide range of atmospheric conditions (i.e. NO between 0.15 and 2&#8201;ppbv and temperature between 25 and 41&#8201;&#176;C) in the atmospheric simulation chamber SAPHIR. These conditions cover remote areas partially influenced by anthropogenic NO emissions, giving a regeneration efficiency of OH close to one, and areas like the Amazonian rainforest with very low NO, resulting in a surprisingly high regeneration efficiency of 0.5, i.e. a factor of 2 to 3 higher than explainable in the absence of unimolecular reactions. The measured radical concentrations were compared to model calculations and the best agreement was observed when at least 50&#8201;% of the total loss of isoprene peroxy radicals conformers (weighted by their abundance) occurs via isomerization reactions for NO lower than 0.2 parts per billion (ppbv). For these levels of NO, up to 50&#8201;% of the OH radicals are regenerated from the products of the 1,6 &#945;-hydroxy-hydrogen shift (1,6-H shift) of Z-&#948;-RO2 radicals through photolysis of an unsaturated hydroperoxy aldehyde (HPALD) and/or through the fast aldehyde hydrogen shift (rate constant &#8764;&#8201;10&#8201;s&#8722;1 at 300&#8201;K) in di-hydroperoxy carbonyl peroxy radicals (di-HPCARP-RO2), depending on their relative yield. The agreement between all measured and modelled trace gases (hydroxyl, hydroperoxy and organic peroxy radicals, carbon monoxide and the sum of methyl vinyl ketone, methacrolein and hydroxyl hydroperoxides) is nearly independent on the adopted yield of HPALD and di-HPCARP-RO2 as both degrade relatively fast (<&#8201;1&#8201;h), forming OH radical and CO among other products. Taking into consideration this and earlier isoprene studies, considerable uncertainties remain on the oxygenated products distribution, which affect radical levels and organic aerosol downwind of unpolluted isoprene dominated regions.

show abstract

Photochemistry of the Troposphere

Cited by 70 publications

References 187 publications

On the Relationship Between Hydrogen Saturation in the Tropical Atlantic Ocean and Nitrogen Fixation by the Symbiotic Diazotroph UCYN‐A

On the Relationship Between Hydrogen Saturation in the Tropical Atlantic Ocean and Nitrogen Fixation by the Symbiotic Diazotroph UCYN‐A

Technical Note: Formal blind intercomparison of OH measurements: results from the international campaign HOxComp

Importance of isomerization reactions for the OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

Contact Info

Product

Resources

About