The carbon isotopic signature (δ¹³CH₄) of several methane sources in Germany (around Heidelberg and in North Rhine-Westphalia) were characterised. Mobile measurements of the plume of CH₄ sources are carried out using an analyser based on cavity ring-down spectroscopy (CRDS). To achieve precise results a CRDS analyser, which measures methane (CH₄), carbon dioxide (CO₂) and their ¹³C-to-¹²C ratios, was characterised especially with regard to cross sensitivities of composition differences of the gas matrix in air samples or calibration tanks. The two most important gases which affect δ¹³CH₄ are water vapour (H₂O) and ethane (C₂H₆). To avoid the cross sensitivity with H₂O, the air is dried with a Nafion dryer during mobile measurements. C₂H₆ is typically abundant in natural gases and thus in methane plumes or samples originating from natural gas. A C₂H₆ correction and calibration are essential to obtain accurate δ¹³CH₄ results, which can deviate by up to 3 ‰ depending on whether a C₂H₆ correction is applied. The isotopic signature is determined with the Miller–Tans approach and the York fitting method. During 21 field campaigns the mean δ¹³CH₄ signatures of three dairy farms ($-\mathrm{63.9}\pm \mathrm{0.9}\mathrm{‰}$ ), a biogas plant ($-\mathrm{62.4}\pm \mathrm{1.2}\mathrm{‰}$ ), a landfill ($-\mathrm{58.7}\pm \mathrm{3.3}\mathrm{‰}$ ), a wastewater treatment plant ($-\mathrm{52.5}\pm \mathrm{1.4}\mathrm{‰}$ ), an active deep coal mine ($-\mathrm{56.0}\pm \mathrm{2.3}\mathrm{‰}$ ) and two natural gas storage and gas compressor stations ($-\mathrm{46.1}\pm \mathrm{0.8}\mathrm{‰}$ ) were recorded. In addition, between December 2016 and November 2018 gas samples from the Heidelberg natural gas distribution network were measured with a mean δ¹³CH₄ value of $-\mathrm{43.3}\pm \mathrm{0.8}\mathrm{‰}$ . Contrary to previous measurements between 1991 and 1996 by Levin et al. (1999), no strong seasonal cycle is shown.

We evaluated NOVAC (Network for Observation of Volcanic and Atmospheric Change) gas emission data from the 2015 eruption of the Cotopaxi volcano (Ecuador) for BrO∕SO₂ molar ratios. The BrO∕SO₂ molar ratios were very small prior to the phreatomagmatic explosions in August 2015, significantly higher after the explosions, and continuously increasing until the end of the unrest period in December 2015. These observations together with similar findings in previous studies at other volcanoes (Mt. Etna, Nevado del Ruiz, Tungurahua) suggest a possible link between a drop in BrO∕SO₂ and a future explosion. In addition, the observed relatively high BrO∕SO₂ molar ratios after December 2015 imply that bromine degassed predominately after sulfur from the magmatic melt. Furthermore, statistical analysis of the data revealed a conspicuous periodic pattern with a periodicity of about 2 weeks in a 3-month time series. While the time series is too short to rule out a chance recurrence of transient geological or meteorological events as a possible origin for the periodic signal, we nevertheless took this observation as a motivation to examine the influence of natural forcings with periodicities of around 2 weeks on volcanic gas emissions. One strong aspirant with such a periodicity are the Earth tides, which are thus central in this study. We present the BrO∕SO₂ data, analyse the reliability of the periodic signal, discuss a possible meteorological or eruption-induced origin of this signal, and compare the signal with the theoretical ground surface displacement pattern caused by the Earth tides. Our central result is the observation of a significant correlation between the BrO∕SO₂ molar ratios with the north–south and vertical components of the calculated tide-induced surface displacement with correlation coefficients of 47 and 36 %, respectively. From all other investigated parameters, only the correlation between the BrO∕SO₂ molar ratios and the relative humidity in the local atmosphere resulted in a comparable correlation coefficient of about 33 %.

Volcanic emissions are a source of halogens in the atmosphere. Rapid reactions convert the initially emitted hydrogen halides (HCl, HBr, and HI) into reactive species such as BrO, Br₂, BrCl, ClO, OClO, and IO. The activation reaction mechanisms in the plume consume ozone (O₃), which is entrained by ambient air that is mixed into the plume. In this study, we present observations of the oxidation of bromine, chlorine, and iodine during the first 11 min following emission, examining the plume from Santiago crater of the Masaya volcano in Nicaragua. Two field campaigns were conducted: one in July 2016 and one in September 2016. The sum of the reactive species of each halogen was determined by gas diffusion denuder sampling followed by gas chromatography–mass spectrometry (GC-MS) analysis, whereas the total halogens and sulfur concentrations were obtained by alkaline trap sampling with subsequent ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Both ground and airborne sampling with an unoccupied aerial vehicle (carrying a denuder sampler in combination with an electrochemical SO₂ sensor) were conducted at varying distances from the crater rim. The in situ measurements were accompanied by remote sensing observations (differential optical absorption spectroscopy; DOAS). The reactive fraction of bromine increased from 0.20 ± 0.13 at the crater rim to 0.76 ± 0.26 at 2.8 km downwind, whereas chlorine showed an increase in the reactive fraction from (2.7 ± 0.7) × 10⁻⁴ to (11 ± 3) × 10⁻⁴ in the first 750 m. Additionally, a reactive iodine fraction of 0.3 at the crater rim and 0.9 at 2.8 km downwind was measured. No significant change in BrO $/$ SO₂ molar ratios was observed with the estimated age of the observed plume ranging from 1.4 to 11.1 min. This study presents a large complementary data set of different halogen compounds at Masaya volcano that allowed for the quantification of reactive bromine in the plume of Masaya volcano at different plume ages. With the observed field data, a chemistry box model (Chemistry As A Boxmodel Application Module Efficiently Calculating the Chemistry of the Atmosphere; CAABA/MECCA) allowed us to reproduce the observed trend in the ratio of the reactive bromine to total bromine ratio. An observed contribution of BrO to the reactive bromine fraction of about 10 % was reproduced in the first few minutes of the model run.

Masaya (Nicaragua, 12.0^∘ N, 86.2^∘ W; 635 m a.s.l.) is one of the few volcanoes hosting a lava lake, today. This study has two foci: (1) discussing the state of the art of long-term SO₂ emission flux monitoring with the example of Masaya and (2) the provision and discussion of a continuous data set on volcanic gas data with a large temporal coverage, which is a major extension of the empirical database for studies in volcanology as well as atmospheric bromine chemistry. We present time series of SO₂ emission fluxes and $\mathrm{BrO}/{\mathrm{SO}}_{\mathrm{2}}$ molar ratios in the gas plume of Masaya from March 2014 to March 2020 – covering the three time periods (1) before the lava lake appearance, (2) a period of high lava lake activity (November 2015 to May 2018), and (3) after the period of high lava lake activity. For these three time periods, we report average SO₂ emission fluxes of (1000±200), (1000±300), and (700±200) t d⁻¹ and average $\mathrm{BrO}/{\mathrm{SO}}_{\mathrm{2}}$ molar ratios of $(\mathrm{2.9}\pm \mathrm{1.5})\times {\mathrm{10}}^{-\mathrm{5}}$ , $(\mathrm{4.8}\pm \mathrm{1.9})\times {\mathrm{10}}^{-\mathrm{5}}$ , and $(\mathrm{5.5}\pm \mathrm{2.6})\times {\mathrm{10}}^{-\mathrm{5}}$ . Our SO₂ emission flux retrieval is based on a comprehensive investigation of various aspects of spectroscopic retrievals, the wind conditions, and the plume height. We observed a correlation between the SO₂ emission fluxes and the wind speed in the raw data. We present a partial correction of this artefact by applying dynamic estimates for the plume height as a function of the wind speed. Our retrieved SO₂ emission fluxes are on average a factor of 1.4 larger than former estimates based on the same data. Further, we observed different patterns in the $\mathrm{BrO}/{\mathrm{SO}}_{\mathrm{2}}$ time series: (1) an annual cyclicity with amplitudes between 1.4 and $\mathrm{2.5}\times {\mathrm{10}}^{-\mathrm{5}}$ and a weak semi-annual modulation, (2) a step increase by $\mathrm{0.7}\times {\mathrm{10}}^{-\mathrm{5}}$ in late 2015, (3) a linear trend of $\mathrm{1.4}\times {\mathrm{10}}^{-\mathrm{5}}$ per year from November 2015 to March 2018, and (4) a linear trend of $-\mathrm{0.8}\times {\mathrm{10}}^{-\mathrm{5}}$ per year from June 2018 to March 2020. The step increase in 2015 coincided with the lava lake appearance and was thus most likely caused by a change in the magmatic system. We suggest that the cyclicity might be a manifestation of meteorological cycles. We found an anti-correlation between the $\mathrm{BrO}/{\mathrm{SO}}_{\mathrm{2}}$ molar ratios and the atmospheric water concentration (correlation coefficient of −0.47) but, in contrast to that, neither a correlation with the ozone mixing ratio (+0.21) nor systematic dependencies between the $\mathrm{BrO}/{\mathrm{SO}}_{\mathrm{2}}$ molar ratios and the atmospheric plume age for an age range of 2–20 min after the release from the volcanic edifice. The two latter observations indicate an early stop of the autocatalytic transformation of bromide Br⁻ solved in aerosol particles to atmospheric BrO.

How to feed a growing global population in a secure and sustainable way? The conventional, biogenic agriculture has yet failed to provide a reliable concept which circumvents its severe environmental externalities—such as the massive use of land area, water for irrigation, fertilizer, pesticides, herbicides, and fossil fuel. In contrast, the artificial synthesis of carbohydrates from atmospheric carbon dioxide, water, and renewable energy would allow not only for a highly reliable production without those externalities, but would also allow to increase the agricultural capacities of our planet by several orders of magnitude. All required technology is either commercially available or at least developed on a lab-scale (at least for sugar). No directed research has, however, yet been conducted towards an industry-scale carbohydrate synthesis because the biogenic carbohydrate production was economically more competitive. Taking the environmental and socio-economic externalities of the conventional sugar production into account, this economical narrative has to be questioned. We estimate the production costs of artificial sugar at ~1 €/kg. While the today's spot market price for conventional sugar is about 0.3 €/kg, we estimate its total costs (including external costs) at ≥0.9 €/kg in humid regions and ≥2 €/kg in semi-arid regions. Accordingly, artificial sugar appears already today to be the less expensive way of production. The artificial sugar production allows in principle also for a subsequent synthesis of other carbohydrates such as starch. These synthetic products could directly supply a large fraction of the human calorie requirements and could be in addition used as a feedstock to microorganisms, fungi, insects, or livestock in order to enhance the sustainability of the remaining biogenic production of, e.g., fats and proteins. This manuscript aims at rising research interest and awareness for a transition to a non-agricultural and more resource-conserving way to supply carbohydrates for food and feed.

Long-term measurements of volcanic gas emissions conducted during the last decade suggest that under certain conditions the magnitude or chemical composition of volcanic emissions exhibits periodic variations with a period of about 2 weeks. A possible cause of such a periodicity can be attributed to the Earth tidal potential. The phenomenology of such a link has been debated for long, but no quantitative model has yet been proposed. The aim of this paper is to elucidate whether a causal link between tidal forcing and variations in volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations and derive a periodical vertical magma displacement in the conduit with an amplitude of 0.1–1 m, depending on the geometry and physical state of the magmatic system. We find that while the tide-induced vertical magma displacement presumably has no significant direct effect on the volatile solubility, the differential magma flow across the radial conduit profile may result in a significant increase in the bubble coalescence rate at a depth of several kilometres by up to several multiples of 10 %. Because bubble coalescence facilitates separation of gas from magma and thus enhances volatile degassing, we argue that the derived tidal variation may propagate to a manifestation of varying volcanic degassing behaviour. The presented model provides a first basic framework which establishes an analytical understanding of the link between the Earth tides and volcanic degassing.