Preprints
https://doi.org/10.5194/acp-2018-1325
https://doi.org/10.5194/acp-2018-1325
17 May 2019
 | 17 May 2019
Status: this preprint was under review for the journal ACP. A final paper is not foreseen.

Segregation in the Atmospheric Boundary Layer: The Case of OH – Isoprene

Ralph Dlugi, Martina Berger, Chinmay Mallik, Anywhere Tsokankunku, Michael Zelger, Otávio C. Acevedo, Efstratios Bourtsoukidis, Andreas Hofzumahaus, Jürgen Kesselmeier, Gerhard Kramm, Daniel Marno, Monica Martinez, Anke C. Nölscher, Huug Ouwersloot, Eva Y. Pfannerstill, Franz Rohrer, Sebastian Tauer, Jonathan Williams, Ana-Maria Yáñez-Serrano, Meinrat O. Andreae, Hartwig Harder, and Matthias Sörgel

Abstract. In the atmospheric boundary layer (ABL), incomplete mixing (i.e., segregation) results in reduced chemical reaction rates compared to those expected from mean values and rate constants derived under well mixed conditions. Recently, segregation has been suggested as a potential cause of discrepancies between modelled and measured OH radical concentrations, especially under high isoprene conditions. Therefore, the influence of segregation on the reaction of OH radicals with isoprene has been investigated by modelling studies and one ground-based and one aircraft campaign.

In this study, we measured isoprene and OH radicals with high time resolution in order to directly calculate the influence of segregation in a low-NOx and high-isoprene environment in the central Amazon basin. The calculated intensities of segregation (Is) at the Amazon Tall Tower Observatory (ATTO) above canopy top are in the range of values determined at a temperate deciduous forest (ECHO-campaign) in a high-NOx low-isoprene environment, but stay below 10 %. To establish a more general idea about the causes of segregation and their potential limits, further analysis was based on the budget equations of isoprene mixing ratios, the variance of mixing ratios, and the balance of the intensity of segregation itself. Furthermore, it was investigated if a relation of Is to the turbulent isoprene surface flux can be established theoretically and empirically, as proposed previously. A direct relation is not given and the amount of variance in Is explained by the isoprene flux will be higher the less the influence from other processes (e.g., vertical advection) is and will therefore be greater near the surface. Although ground based values of Is from ATTO and ECHO are in the same range, we could identify different dominating processes driving Is. For ECHO the normalized variance of isoprene had the largest contribution, whereas for ATTO the different transport terms expressed as a residual were dominating. To get a more general picture of Is and its potential limits in the ABL, we also compared these ground based measurements to ABL modelling studies and results from an aircraft campaign. The ground based measurements show the lowest values of the degree of inhomogenous mixing (< 20 %, mostly below 10 %). These values increase if the contribution of lower frequencies is added. Values integrated over the whole boundary layer (modelling studies) are in the range from 10 % to 30 % and aircraft measurements integrating over different landscapes are amongst the largest reported. This presents evidence that larger scale heterogeneities in land surface properties contribute substantially to Is.

This preprint has been withdrawn.

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Ralph Dlugi, Martina Berger, Chinmay Mallik, Anywhere Tsokankunku, Michael Zelger, Otávio C. Acevedo, Efstratios Bourtsoukidis, Andreas Hofzumahaus, Jürgen Kesselmeier, Gerhard Kramm, Daniel Marno, Monica Martinez, Anke C. Nölscher, Huug Ouwersloot, Eva Y. Pfannerstill, Franz Rohrer, Sebastian Tauer, Jonathan Williams, Ana-Maria Yáñez-Serrano, Meinrat O. Andreae, Hartwig Harder, and Matthias Sörgel

Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Ralph Dlugi, Martina Berger, Chinmay Mallik, Anywhere Tsokankunku, Michael Zelger, Otávio C. Acevedo, Efstratios Bourtsoukidis, Andreas Hofzumahaus, Jürgen Kesselmeier, Gerhard Kramm, Daniel Marno, Monica Martinez, Anke C. Nölscher, Huug Ouwersloot, Eva Y. Pfannerstill, Franz Rohrer, Sebastian Tauer, Jonathan Williams, Ana-Maria Yáñez-Serrano, Meinrat O. Andreae, Hartwig Harder, and Matthias Sörgel
Ralph Dlugi, Martina Berger, Chinmay Mallik, Anywhere Tsokankunku, Michael Zelger, Otávio C. Acevedo, Efstratios Bourtsoukidis, Andreas Hofzumahaus, Jürgen Kesselmeier, Gerhard Kramm, Daniel Marno, Monica Martinez, Anke C. Nölscher, Huug Ouwersloot, Eva Y. Pfannerstill, Franz Rohrer, Sebastian Tauer, Jonathan Williams, Ana-Maria Yáñez-Serrano, Meinrat O. Andreae, Hartwig Harder, and Matthias Sörgel

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Short summary
Incomplete mixing (segregation) results in reduced chemical reaction rates compared to those expected from mean values and rate constants. Segregation has been suggested to cause discrepancies between modelled and measured OH radical concentrations. In this work, we summarize the intensities of segregation for the reaction of OH and isoprene for different field and modelling studies and compare those to our results from measurements in a pristine environment.
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