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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Atmos. Meas. Tech. Discuss., 8, 2767–2791, 2015 www.atmos-meas-tech-discuss.net/8/2767/2015/ doi:10.5194/amtd-8-2767-2015 AMTD © Author(s) 2015. CC Attribution 3.0 License. 8, 2767–2791, 2015 This discussion paper is/has been under review for the journal Atmospheric Measurement Greenhouse gas Techniques (AMT). Please refer to the corresponding final paper in AMT if available. emissions of Berlin – Part 2: Observed time Use of portable FTIR spectrometers for series of XCO2 and XCH4 detecting greenhouse gas emissions of F. Hase et al. the megacity Berlin – Part 2: Observed Title Page time series of XCO2 and XCH4 Abstract Introduction F. Hase1, M. Frey1, T. Blumenstock1, J. Groß1, M. Kiel1, R. Kohlhepp2, Conclusions References G. Mengistu Tsidu1,4, K. Schäfer3, M. K. Sha1, and J. Orphal1 Tables Figures 1Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research (IMK-ASF), Karlsruhe, Germany J I 2German Weather Service, Offenbach, Germany 3 Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research J I (IMK-IFU), Garmisch-Partenkirchen, Germany Back Close 4Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia Full Screen / Esc Received: 19 February 2015 – Accepted: 24 February 2015 – Published: 13 March 2015 Correspondence to: F. Hase ([email protected]) Printer-friendly Version Published by Copernicus Publications on behalf of the European Geosciences Union. Interactive Discussion 2767 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract AMTD Five portable Bruker EM27/SUN FTIR spectrometers have been used for the accurate 8, 2767–2791, 2015 and precise observation of column averaged abundances of CO2 and CH4 around the megacity Berlin. In the first part of this work (Frey et al., 2015) we have presented the 5 various measures that were undertaken to ensure that the observations are consistent Greenhouse gas between sites, accurate and precise. Here, we present the recorded time series of emissions of Berlin – X CH4 and X CO2 and demonstrate that the CO2 emissions of Berlin can be clearly Part 2: Observed time identified in the observations. A simple dispersion model is applied which indicates series of XCO and −1 2 a total strength of the Berlin source of about 0.8 tCO2 s . In the Supplement of this XCH4 10 work, we provide the measured dataset and auxiliary data. We hope that the model F. Hase et al. community will exploit this unique dataset for state-of-the art inversion studies of CO2 and CH4 sources in the Berlin area. Title Page 1 Introduction Abstract Introduction The application of portable FTIR spectrometers for the observation of column-averaged Conclusions References 15 CO2 and CH4 abundances holds great promises with respect to the quantification of sources and sinks of greenhouse gases on regional and smaller scales. Although in- Tables Figures situ measurements at the ground can be performed with unrivaled precision and accu- racy, these measurements suffer from the fact that they detect local variations and so J I are heavily influenced by local contributions and by details of the vertical mixing. Use J I 20 of in-situ measurements on different altitude levels (tall tower, aircraft) improves the representativeness considerably, but is a rather expensive approach. Current space Back Close based remote sensing observations are useful for the quantification of sources and Full Screen / Esc sinks on continental scales, but still suffer from limited precision, limited density of ob- servations, and biases related to details of atmospheric scattering properties. Ground- Printer-friendly Version 25 based observations using high-resolution laboratory spectrometers as performed by TCCON (Total Carbon Column Observing Network, Wunch et al., 2011) can provide Interactive Discussion 2768 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | column averaged abundances with reference precision and accuracy, but the number of sites is limited and the stations are not mobile. Portable FTIR spectrometers there- AMTD fore are a very promising complement to current techniques, because they can probe 8, 2767–2791, 2015 larger sample volumes than in-situ and smaller scales than current space-based sen- 5 sors or globally distributed ground-based remote sensing networks. In this work, we demonstrate the approach of using solar absorption spectra recorded with small low- Greenhouse gas resolution FTIR spectrometers at several sites distributed around a source region for an emissions of Berlin – estimation of the encircled source strength. The demonstration is based on a campaign Part 2: Observed time we performed from 23 June 2014 to 11 July 2014 around Berlin using five spectrome- series of XCO2 and 10 ters. The site locations are detailed in the first part of this work. Due to somewhat un- XCH4 favourable weather conditions, we were able to perform simultaneous measurements at all sites only on 10 days during the demonstration campaign. However, it should F. Hase et al. be noted that such spectrometers can be installed for longer periods of operation in weather-resistant shelters and operated automatically – in order to from a permanent Title Page 15 component of future monitoring systems. Due to the long lifetimes of CO2 and CH4, each individual source contribution is Abstract Introduction a weak signal superimposed on the average column-averaged background abundance. Conclusions References Therefore, ensuring a common calibration of all involved spectrometers and demon- strating their instrumental stability is of utmost importance for the proposed method. Tables Figures 20 In the first part of this work, we have described the rigorous calibration procedures we applied for the EM27/SUN spectrometers involved in this campaign and the excellent J I instrumental stability which our pre- and after campaign tests revealed. J I Back Close 2 Weather and prevailing winds and auxiliary measurements Full Screen / Esc In Table 1, we collect the main characteristics of each measurement day. We list the 25 number of observations available at each site, and deduce a daily quality flag according Printer-friendly Version to the overall data availability. Furthermore, the wind speeds and prevailing wind direc- Interactive Discussion tions in the boundary layer are provided. The best measurement days with measure- 2769 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ments during throughout most of the day (solar elevation angle > 20◦) were 27 June, 3 and 4 July. During these days, prevailing winds were from the West (and South). AMTD Wind speeds were moderate in the range of 5 to 8 kn. Note that although not very well 8, 2767–2791, 2015 covered, the set of observations includes a Sunday (6 July), which is an interesting 5 aspect, as a different temporal pattern and overall strength of emissions is expected on a Sunday than during a working day. Greenhouse gas A very important auxiliary information required for the proper estimation of a source emissions of Berlin – strength is the development of the boundary layer height during each day of observa- Part 2: Observed time tions. IMK-IFU performed continuous ceilometer measurements of the boundary layer series of XCO2 and 10 height during the whole campaign period. The measurements were performed in Berlin XCH4 Neukölln (52.4895◦ N, 13.4309◦ E), 2.5 km to the southeast from the city center. The F. Hase et al. applied ceilometer CL51 from Vaisala GmbH, Hamburg, Germany, is an eye-safe com- mercial mini-lidar system. Ceilometers detect originally the cloud height, but special software provides routine retrievals of up to 5 lifted layers from vertical profiles (verti- Title Page 15 cal gradient) of laser backscatter density data (Münkel, 2007). In the absence of low clouds and precipitation and during scattered clouds, this measurement method esti- Abstract Introduction mates boundary layer height fairly well. The CL51 detects convective layer depths ex- Conclusions References ceeding 2000 m and nocturnal stable layers down to 50 m. The measurements results agree well with those which are determined from profiles of relative humidity and vir- Tables Figures 20 tual potential temperature measured by radiosonde (location of strong height gradient of aerosol backscatter density and relative humidity as well as temperature inversion, J I see Emeis et al., 2012). But radiosondes which are launched routinely twice per day only do not provide sufficient information. Figure 1 shows the ceilometer results for 27 J I June: the developing boundary layer can be nicely seen, reaching an altitude of about Back Close 25 2200 m in the late afternoon. In the case of airborne particles it could be shown earlier Full Screen / Esc that boundary layer information as detected continuously by ceilometers enables the determination of near-surface concentrations from column density data (Schäfer et al., Printer-friendly Version 2008). Interactive Discussion 2770 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 The XH2O, XCO2 and XCH4 timeseries AMTD Figure 2 shows the observed time series of H2O dry air mole fractions. As expected, 8, 2767–2791, 2015 H2O is varying considerably – by about a factor of three – over the campaign period. On the other hand, the agreement between the stations is surprisingly good. This demon- 5 strates the uniform character of the selected area, especially the absence of localized Greenhouse gas dominating sources of atmospheric humidity, which would induce larger differences be- emissions of Berlin – tween the stations. Finally, as the main contribution to the H2O total column originates Part 2: Observed time from the boundary layer, this finding supports the assumption that the boundary layer series of XCO2 and across the whole probed area is well ventilated. XCH4 10 Figures 3 and 4 show the X CO2 and X CH4 values, respectively, as observed by all spectrometers. The dominating synoptic variations which are common to all sites occur F.

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