2D Simulation von Hochwasserszenarien an der Sihl in der Stadt Zürich

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975

Online coupling of pure O2 thermo-optical methods – 14C AMS for source apportionment of carbonaceous aerosols

This paper reports on novel separation methods developed for the direct determination of 14C in organic carbon (OC) and elemental carbon (EC), two sub-fractions of total carbon (TC) of atmospheric air particulate matter. Until recently, separation of OC and EC has been performed off-line by manual and time-consuming techniques that relied on the collection of massive CO2 fractions. We present here two on-line hyphenated techniques between a Sunset OC/EC analyzer and a MICADAS (MIni radioCArbon DAting System) accelerator mass spectrometer (AMS) equipped with a gas ion source. The first implementation facilitates the direct measurement in the low sample size range (<10 lg C) with high throughput on a routine basis, while the second explores the potential for a continuous-flow real-time CO2 gas feed into the ion source. The performance achieved with reference materials and real atmospheric samples will be discussed to draw conclusions on the improvement offered in the field of 14C aerosol source apportionment

Evaluation and Inter-Comparison of Oxygen-Based OC-EC Separation Methods for Radiocarbon Analysis of Ambient Aerosol Particle Samples

Radiocarbon analysis is a widely-used tool for source apportionment of aerosol particles. One of the big challenges of this method, addressed in this work, is to isolate elemental carbon (EC) for 14C analysis. In the first part of the study, we validate a two-step method (2stepCIO) to separate total carbon (TC) into organic carbon (OC) and EC against the EUSAAR_2 thermal-optical method regarding the recovered carbon concentrations. The 2stepCIO method is based on the combustion of OC in pure oxygen at two different temperature steps to isolate EC. It is normally used with a custom-built aerosol combustion system (ACS), but in this project, it was also implemented as a thermal protocol on a Sunset OC-EC analyzer. Results for the recovered EC mass concentration showed poor agreement between the 2stepCIO method on the ACS system and on the Sunset analyzer. This indicates that the EC recovery is sensitive not only to the temperature steps, but also to instrument-specific parameters, such as heating rates. We also found that the EUSAAR_2 protocol itself can underestimate the EC concentration on untreated samples compared to water-extracted samples. This is especially so for highly loaded filters, which are typical for 14C analysis. For untreated samples, the EC concentration on long-term filter samples (two to five days sampling time) was 20–45% lower than the sum of EC found on the corresponding 24-h filter samples. For water-extracted filter samples, there was no significant difference between long-term and the sum of daily filter samples. In the second part of this study, the 14C was measured on EC isolated by the 2stepCIO method and compared to methods from two other laboratories. The different methods agree well within their uncertainty estimates

Isolation and 14C analysis of humic-like substances (HULIS) from ambient aerosol samples

HUmic-LIke Substances (HULIS) are an unresolved complex mixture of organic compounds, which accounts for 12-60% of the total organic carbon (OC) in ambient aerosols (Graber and Rudich, 2006). As the characterization of HULIS is still incomplete and because their composition and amount is strictly method-dependent, a meaningful comparison of different studies about this class of compounds is difficult. Testing of different isolation methodologies resulted in a straightforward HULIS extraction procedure for 14C source apportionment by accelerator mass spectrometry (14C-AMS). The presented methodology corresponds to a modified method of Varga et al. (2001). The complete procedure is summarized as a flow chart in Fig. 1. The procedure blank was quantified in terms of its mass and its 14C/12C ratio by isotopic dilution analysis using a fossil and a modern reference material. Due to this blank, the sample mass for the AMS measurement should exceed 20 µg C for an adequate accuracy and precision of 14C data. The application of the presented method on different ambient aerosol filters strongly indicates modern sources for HULIS

Fossil and Non-fossil Fuel Sources of Organic and Elemental Carbonaceous Aerosol in Beijing, Shanghai, and Guangzhou: Seasonal Carbon Source Variation

We measured the radiocarbon isotope signals in various fractions of carbonaceous aerosols sampled across four seasons (Oct 2013–Jul 2014) in three megacities of China, viz., Beijing, Shanghai, and Guangzhou. The contributions of fossil fuel (FF) and non-fossil fuel (NF) to the carbonaceous aerosol were estimated based on the radiocarbon content in the organic carbon (OC), water-soluble organic carbon (WSOC), water-insoluble organic carbon (WIOC), and elemental carbon (EC). Although NF generated the primary share (> 55%) during autumn in all of the cities, the seasonal contributions of the sources differed by location during the rest of the year. During winter, FF emissions constituted the majority of the carbonaceous pollution (64%) in Beijing, probably as a result of increased coal combustion for heating. On average, the EC, WSOC, and WIOC generated by FF composed ~10%, 35%, and 19% of the total carbon (TC). Overall, NF was identified as the largest source of carbonaceous aerosol in Guangzhou (63%), whereas FF was the largest source, contributing slightly more than NF, in Shanghai (54%). During spring and summer, FF played a greater role than NF in Beijing (~55%) and Guangzhou (~63%); additionally, based on our limited number of samples, it contributed 71% in Shanghai during the latter season, with a significant portion due to fuel combustion (i.e., industrial, vehicular, fishing-boat, and large-vessel emissions)

Basement v3: a modular freeware for river process modelling over multiple computational backends

Modelling river physical processes is of critical importance for flood protection, river management and restoration of riverine environments. Developments in algorithms and computational power have led to a wider spread of river simulation tools. However, the use of two-dimensional models can still be hindered by complexity in the setup and the high computational costs. Here we present the freeware basement version 3, a flexible tool for two-dimensional river simulations that bundles solvers for hydrodynamic, morphodynamic and scalar advection-diffusion processes. basement leverages different computational platforms (multi-core CPUs and graphics processing units GPUs) to enable the simulation of large domains and long-term river processes. The adoption of a fully costless workflow and a light GUI facilitate its broad utilization. We test its robustness and efficiency in a selection of benchmarks. Results confirm that basement could be an efficient and versatile tool for research, engineering practice and education in river modelling.ISSN:1364-8152ISSN:1873-672

Quantification of Fossil and Non-Fossil SOA from Combined 14C/AMS-PMF Analysis for the SOAS Field Campaign

The Southern Oxidant and Aerosol Study (SOAS) was a large field campaign during June-July 2013 in the southeast USA (Hidy et al., 2014; Hu et al., 2015; Carlton et al., 2018). Vast forested areas emitting large amounts of organic compounds and proximity to metropolitan areas present an ideal environment to investigate the influence of anthropogenic emissions on the biogenic secondary organic aerosol (SOA) formation. The main site of this study, located in rural Centreville, AL, was equipped with a wide variety of state-of-the-art analytical instruments. This project focuses on the source apportionment of the organic carbon (OC) fraction of ambient aerosol samples, through combination of radiocarbon (14C) data with positive matrix factorization information from online aerosol mass spectrometry measurements (AMS-PMF). Analysis of the long-lived radioactive isotope 14C is a unique source apportionment tool: it unambiguously separates fossil from non-fossil sources, as 14C has completely decayed in fossil fuels, whereas modern materials have the contemporary radiocarbon level (Szidat, 2009). 14C was measured for total carbon (TC) and elemental carbon (EC) (Zhang et al., 2012) from quartz filters that were collected at Centreville with daily resolution. This allowed the apportionment of fossil vs. non-fossil sources for EC and OC. Although OC mainly originated from non-fossil sources, a certain fraction was attributed to emissions from fossil sources. These results were compared with AMS-PMF data from a high-resolution time-of-flight AMS (Hu et al., 2015), which identified six different factors, i.e. biomass burning organic aerosol (BBOA), SOA formed through direct condensation of low-volatility oxidation products from isoprene (ISOPOOH-SOA), isoprene epoxydiols-derived SOA (IEPOX-SOA), low-oxidized oxygenated organic aerosol I, attributed to mostly biogenic sources (LO OOAI), low-oxidized OOA II, attributed mostly to anthropogenic sources (LO-OOAII) and more-oxidized OOA (MO-OOA). On average, the less well-understood fractions LO-OOAI, LO-OOAII and MO-OOA comprise ~3/4 of the total organic aerosol mass. 14C analysis of EC enables the distinction of sources of this carbonaceous aerosol fraction between fossil-fuel combustion (mainly from traffic) and biomass burning. It indicated a larger contribution from biomass burning compared to other source apportionment techniques or results from bottom-up emission inventories. The combination of 14C and AMS-PMF analysis provides the potential to apportion fossil vs. non-fossil sources for components for which the non-fossil fraction cannot by analyzed directly, such as SOA (Zotter et al., 2014). In this work, we present such results for the SOAS campaign based on Markov chain Monte Carlo calculations to gain more insight into the sources of SOA precursors. LO-OOAI, LO-OOAII and MO-OOA reveal different contributions of fossil and non-fossil sources, which allows a better understanding of these AMS-PMF factors. Carlton, A. M., et al. (2018), Bull. Am. Met. Soc., in press. Hidy, G. M., et al. (2014), Atmos. Chem. Phys., 14, 11893-11914. Hu, W. W., et al. (2015), Atmos. Chem. Phys., 15, 11807-11833. Szidat, S. (2009), Chimia, 63, 157-161. Zhang, Y. L., et al., (2012) Atmos. Chem. Phys., 12 (22), 10841-10856. Zotter, P., et al. (2014), J. Geophys. Res. Atmos., 119, 6818–6835

The importance of non-fossil sources in carbonaceous aerosols in a megacity of central China during the 2013 winter haze episode: A source apportionment constrained by radiocarbon and organic tracers

To determine the causes of a severe haze episode in January 2013 in China, a source apportionment of different carbonaceous aerosols (CAs) was conducted in a megacity in central China (Wuhan, Hubei Province) by using the measurements of radiocarbon and molecular organic tracers. Non-fossil sources (e.g., domestic biofuel combustion and biogenic emissions) were found to be responsible for 62% ± 5% and 26% ± 8% of organic carbon (OC) and elemental carbon (EC) components by mass, respectively. Nonfossil sources contributed 57% ± 4% to total CAs in this large-scale haze event, whereas fossil-fuel sources were less dominant (43% ± 4%). The CAs were composed of secondary organic carbon (SOC; 46% ± 10%), primary fossil-fuel carbon (29% ± 4%) and primary biomass-burning carbon (25% ± 10%). Although SOC was formed mainly from non-fossil sources (70% ± 4%), the role of fossil precursors was substantial (30% ± 4%), much higher than at the global scale. Combined measurement of organic tracers and radiocarbon showed that most non-fossil SOC was probably derived from biomass burning during this long-lasting haze episode in central China