Abstract
Abstract. We describe and test a new versatile software tool for processing eddy covariance and disjunct eddy covariance flux data. We present an evaluation based on urban non-methane volatile organic compound (NMVOC) measurements using a proton transfer reaction quadrupole interface time-of-flight mass spectrometer (PTR-QiTOF-MS) at the Innsbruck Atmospheric Observatory. The code is based on MATLAB® and can be easily configured to process high-frequency, low-frequency and disjunct data. It can be applied to a wide range of analytical setups for NMVOC and other trace gas measurements, and is tailored towards the application of noisy data, where lag time corrections become challenging. Several corrections and quality control routines are implemented to obtain the most reliable results. The software is open source, so it can be extended and adjusted to specific purposes. We demonstrate the capabilities of the code based on a large urban dataset collected in Innsbruck, Austria, where three-dimensional winds and ambient concentrations of NMVOCs and auxiliary trace gases were sampled with high temporal resolution above an urban canopy. Concomitant measurements of 12C and 13C isotopic NMVOC fluxes allow testing algorithms used for determination of flux limits of detection (LOD) and lag time analysis. We use the high-frequency NMVOC dataset to generate a set of disjunct data and compare these results with the true eddy covariance method. The presented analysis allows testing the theory of disjunct eddy covariance (DEC) in an urban environment. Our findings confirm that the disjunct eddy covariance method can be a reliable tool, even in complex urban environments when fast sensors are not available, but that the increase in random error impedes the ability to detect small fluxes due to higher flux LODs.
Highlights
Eddy covariance (EC) is the method of choice for most micrometeorological studies of turbulent fluxes (e.g., Dabberdt et al, 1993; Aubinet et al, 2012)
The observed variation is caused by the topography and the influence of surface roughness surrounding the urban measurement location, where tall buildings in the vicinity tend to deform the mean streamlines of the airflow from certain directions
We tested the applicability of disjunct eddy covariance and eddy covariance measurements in an urban air matrix using a newly designed software package in MATLAB
Summary
Eddy covariance (EC) is the method of choice for most micrometeorological studies of turbulent fluxes (e.g., Dabberdt et al, 1993; Aubinet et al, 2012). It has been extensively used in atmospheric sciences (e.g., Horst et al, 2004; Oncley et al, 2007; Patton et al, 2011) and biogeochemistry, e.g., Ameriflux, https://ameriflux.lbl.gov/ (last access: 22 March 2020); Euroflux, http://www.europe-fluxdata.eu/ icos (last access: 22 March 2020) (Baldocchi et al, 1988; Fowler et al, 2009; Aubinet et al, 2012; Rannik et al, 2012; Ducker et al, 2018). The use of EC for atmosphere–surface exchange measurements is widespread and a number of commercial, freely distributed closed- and open-source codes for the analysis of EC data are available (e.g., Fratini and Mauder, 2014; Mauder et al, 2008, Metzger et al, 2017).
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