Turbulent exchange and segregation of HO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; radicals and  volatile organic compounds above a deciduous forest

Dlugi, R.; Berger, Michael L.; Zelger, M.; Hofzumahaus, A.; Siese, M.; Holland, F.; Wisthaler, Armin; Grabmer, W.; Hansel, Armin; Koppmann, R.; Kramm, Gerhard; Möllmann-Coers, M.; Knaps, A.

doi:10.5194/acp-10-6215-2010

Cited by 46 publications

(118 citation statements)

References 78 publications

(126 reference statements)

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“…Since DALES explicitly resolves turbulence, including quantities like covariances, the intensities of segregation are calculated directly. Ouwersloot et al (2010) validated the DALES results, confirming the dependence of segregation on the ratio of the turbulent time scale versus the chemical time scales and on the reactant concentration ratio (Schumann, 1989) and giving results in agreement with measurements Dlugi et al, 2010) and previous simulations (Krol et al, 2000;Vinuesa and Vilà-Guerau de Arellano, 2003). We further discuss the dependence of the intensity of segregation on the physical and chemical processes.…”

Section: Formulation and Interpretation Of The Segregationsupporting

confidence: 77%

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On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

et al. 2011

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Abstract. Using a Large-Eddy Simulation model, we have systematically studied the inability of boundary layer turbulence to efficiently mix reactive species. This creates regions where the species are accumulated in a correlated or anti-correlated way, thereby modifying the mean reactivity. We quantify this modification by the intensity of segregation, I S , and analyse the driving mechanisms: heterogeneity of the surface moisture and heat fluxes, various background wind patterns and non-uniform isoprene emissions. The heterogeneous surface conditions are characterized by cool and wet forested patches with high isoprene emissions, alternated with warm and dry patches that represents pasture with relatively low isoprene emissions. For typical conditions in the Amazon rain forest, applying homogeneous surface forcings and in the absence of free tropospheric NO x , the isoprene-OH reaction rate is altered by less than 10 %. This is substantially smaller than the previously assumed I S of 50 % in recent large-scale model analyses of tropical rain forest chemistry. Spatial heterogeneous surface emissions enhance the segregation of species, leading to alterations of the chemical reaction rates up to 20 %. The intensities of segregation are enhanced when the background wind direction is parallel to the borders between the patches and reduced in the case of a perpendicular wind direction. The effects of segregation on trace gas concentrations vary per species. For the highly reactive OH, the differences in concentration averaged over the boundary layer are less than 2 % compared to homogeneous surface conditions, while the isoprene concentration is increased by as much as 12 % due to the reduced chemical reaction rates. These processes take place at the sub-grid scale of chemistry transport models and therefore need to be parameterized.

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Section: Formulation and Interpretation Of The Segregationsupporting

confidence: 77%

“…Butler et al, 2008;Pugh et al, 2010). Observations on the intensity of segregation between OH and isoprene, by relatively fast simultaneous measurements of both compounds over a German deciduous forest, were made by Dlugi et al (2010). However, they only measured at one location and one height, 7 m above the forest canopy.…”

Section: Introductionmentioning

confidence: 99%

On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

et al. 2011

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“…This term represents the effect of turbulence to mix the reactants. However, as shown by Dlugi et al (2010) with measurements and by Ouwersloot et al (2011) with numerical experiments in large-eddy simulation (LES), the influence of segregation on the reaction rates of e.g. OH and isoprene is only small (in the order of 10 %).…”

Section: Representation Of Chemistrymentioning

confidence: 99%

Case study of the diurnal variability of chemically active species with respect to boundary layer dynamics during DOMINO

et al. 2012

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Abstract. We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO (Diel Oxidant Mechanisms in relation to Nitrogen Oxides) campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O 3 -NO x -VOC-HO x diurnal cycle during conditions characterized by a low NO x regime and small O 3 tendencies (less than 1 ppb per hour). By focusing on the budget equations of chemical species in the mixedlayer model, we show that for species like O 3 , NO and NO 2 , the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the diel cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further determine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

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“…An interference from RO 2 radicals would impact HO 2 concentration measurements in the past, when high loads of VOCs including isoprene were present such as during the field campaigns ECHO (Kleffmann et al, 2005;Dlugi et al, 2010) and PRIDE-PRD2006 Lu et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Detection of HO<sub>2</sub> by laser-induced fluorescence: calibration and interferences from RO<sub>2</sub> radicals

Fuchs¹,

Bohn²,

Hofzumahaus³

et al. 2011

Atmos. Meas. Tech.

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Abstract. HO 2 concentration measurements are widely accomplished by chemical conversion of HO 2 to OH including reaction with NO and subsequent detection of OH by laser-induced fluorescence. RO 2 radicals can be converted to OH via a similar radical reaction sequence including reaction with NO, so that they are potential interferences for HO 2 measurements. Here, the conversion efficiency of various RO 2 species to HO 2 is investigated. Experiments were conducted with a radical source that produces OH and HO 2 by water photolysis at 185 nm, which is frequently used for calibration of LIF instruments. The ratio of HO 2 and the sum of OH and HO 2 concentrations provided by the radical source was investigated and was found to be 0.50 ± 0.02. RO 2 radicals are produced by the reaction of various organic compounds with OH in the radical source. Interferences via chemical conversion from RO 2 radicals produced by the reaction of OH with methane and ethane (H-atom abstraction) are negligible consistent with measurements in the past. However, RO 2 radicals from OH plus alkene-and aromaticprecursors including isoprene (mainly OH-addition) are detected with a relative sensitivity larger than 80 % with respect to that for HO 2 for the configuration of the instrument with which it was operated during field campaigns. Also RO 2 from OH plus methyl vinyl ketone and methacrolein exhibit a relative detection sensitivity of 60 %. Thus, previous measurements of HO 2 radical concentrations with this instrument were biased in the presence of high RO 2 radical concentrations from isoprene, alkenes or aromatics, but were not affected by interferences in remote clean environment with no significant emissions of biogenic VOCs, when the OH reactivity was dominated by small alkanes. By reducing the NO concentration and/or the transport time betweenCorrespondence to: H. Fuchs (h.fuchs@fz-juelich.de) NO addition and OH detection, interference from these RO 2 species are suppressed to values below 20 % relative to the HO 2 detection sensitivity. The HO 2 conversion efficiency is also smaller by a factor of four, but this is still sufficient for atmospheric HO 2 concentration measurements for a wide range of conditions.

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Turbulent exchange and segregation of HO<sub>x</sub> radicals and volatile organic compounds above a deciduous forest

Cited by 46 publications

References 78 publications

On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

Case study of the diurnal variability of chemically active species with respect to boundary layer dynamics during DOMINO

Detection of HO<sub>2</sub> by laser-induced fluorescence: calibration and interferences from RO<sub>2</sub> radicals

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Turbulent exchange and segregation of HO&lt;sub&gt;x&lt;/sub&gt; radicals and volatile organic compounds above a deciduous forest

Cited by 46 publications

References 78 publications

On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

Case study of the diurnal variability of chemically active species with respect to boundary layer dynamics during DOMINO

Detection of HO&lt;sub&gt;2&lt;/sub&gt; by laser-induced fluorescence: calibration and interferences from RO&lt;sub&gt;2&lt;/sub&gt; radicals

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Turbulent exchange and segregation of HO<sub>x</sub> radicals and volatile organic compounds above a deciduous forest

Detection of HO<sub>2</sub> by laser-induced fluorescence: calibration and interferences from RO<sub>2</sub> radicals