Wearing surgical masks or other similar face coverings can reduce the emission of expiratory particles produced via breathing, talking, coughing, or sneezing. Although it is well established that some fraction of the expiratory airflow leaks around the edges of the mask, it is unclear how these leakage airflows affect the overall efficiency with which masks block emission of expiratory aerosol particles. Here, we show experimentally that the aerosol particle concentrations in the leakage airflows around a surgical mask are reduced compared to no mask wearing, with the magnitude of reduction dependent on the direction of escape (out the top, the sides, or the bottom). Because the actual leakage flowrate in each direction is difficult to measure, we use a Monte Carlo approach to estimate flow-corrected particle emission rates for particles having diameters in the range 0.5-20 μm. in all orientations. From these, we derive a flow-weighted overall number-based particle removal efficiency for the mask. The overall mask efficiency, accounting both for air that passes through the mask and for leakage flows, is reduced compared to the through-mask filtration efficiency, from 93 to 70% for talking, but from only 94-90% for coughing. These results demonstrate that leakage flows due to imperfect sealing do decrease mask efficiencies for reducing emission of expiratory particles, but even with such leakage surgical masks provide substantial control.

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Expiratory aerosol particle escape from surgical masks due to imperfect sealing.

Abstract Open-vent, persistently degassing volcanoes—such as Stromboli and Etna (Italy), Villarrica (Chile), Bagana and Manam (Papua New Guinea), Fuego and Pacaya (Guatemala) volcanoes—produce high gas fluxes and infrequent violent strombolian or ‘paroxysmal’ eruptions that erupt very little magma. Here we draw on examples of open-vent volcanic systems to highlight the principal characteristics of their degassing regimes and develop a generic model to explain open-vent degassing in both high and low viscosity magmas and across a range of tectonic settings. Importantly, gas fluxes from open-vent volcanoes are far higher than can be supplied by erupting magma and independent migration of exsolved volatiles is integral to the dynamics of such systems. The composition of volcanic gases emitted from open-vent volcanoes is consistent with its derivation from magma stored over a range of crustal depths that in general requires contributions from both magma decompression (magma ascent and/or convection) and iso- and polybaric second boiling processes. Prolonged crystallisation of water-rich basalts in crustal reservoirs produces a segregated exsolved hydrous volatile phase that may flux through overlying shallow magma reservoirs, modulating heat flux and generating overpressure in the shallow conduit. Small fraction water-rich melts generated in the lower and mid-crust may play an important role in advecting volatiles to subvolcanic reservoirs. Excessive gas fluxes at the surface are linked to extensive intrusive magmatic activity and endogenous crustal growth, aided in many cases by extensional tectonics in the crust, which may control the longevity and activity of open-vent volcanoes. There is emerging abundant geophysical evidence for the existence of a segregated exsolved magmatic volatile phase in magma storage regions in the crust. Here we provide a conceptual picture of gas-dominated volcanoes driven by magmatic intrusion and degassing throughout the crust. 

/pdf/open-vent-volcanoes-fuelled-by-depth-integrated-magma-3cs1dioj.pdf

Open-vent volcanoes fuelled by depth-integrated magma degassing

In June 2007 and July 2010 spectroscopic measurements and chemical in-situ studies were carried out at Nyiragongo
volcano located 15 km north of the city Goma, North Kivu region (DRC), both at the crater rim and within the crater itself, next to the lava lake. Nyiragongo volcano belongs to the Virunga volcanic chain and it is associated with the Western branch of the Great Rift Valley. The volcanism at Nyiragongo is caused by the rifting of the Earth’s crust where two parts of the African plates are breaking apart. Niyragongo crater contains the biggest lava lake on Earth and it is considered one of the most active volcanoes in the world.
The ground-based remote sensing technique MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy)
using scattered sunlight has been applied during both field trips at the crater rim of the volcano to
measure sulphur dioxide, halogen oxides and nitrogen oxide. Additionally filter pack and spectroscopic in-situ carbon dioxide measurements were carried out, as well as SO2 flux measurements by a scanning DOAS instrument
from the NOVAC project at the flank of the volcano.
Nyiragongo is the first rift volcano where halogen oxides have been observed in the plume.
Observations indicate that the gas composition of Nyiragongo might change with a changing lava lake level in
short and long-term time scales. Before and during an overflow of the lava lake the molar ratios of BrO/SO2 were
decreasing in 2007 and 2010 from about 3.10-5 to about 0 (below the detection limit). Such a decreasing trend
was also observed before and during the eruption of Mt. Etna 2006 and 2008.
In a larger timescale between 2007 and 2010 the molar ratios of S/Cl and CO2/SO2 generally decreased from 6.7 -
16.5 to 0.7 – 2.1, from 5 -10 to 1 - 5, respectively. The lower S/Cl and CO2/SO2 could lead to the conclusion that
the magma reservoir below Niyragongo has had no new input from a deeper source.
The chemical composition as well as its temporal variability within the volcanic plume from the lava lake will be discussed, as well as its implication on the understanding of the dynamics of the plumbing system of this volcano.

/pdf/gas-emission-measurements-of-the-active-lava-lake-of-3a0yetqks2.pdf

Gas emission measurements of the active lava lake of Nyiragongo, DR Congo

. A multi-rotor drone has been adapted for studies of volcanic gas plumes. This adaptation includes improved capacity for high-altitude and long-range, real-time SO2 concentration monitoring, long-range manual control, remotely activated bag sampling and plume speed measurement
capability. The drone is capable of acting as a stable platform for various instrument configurations, including multi-component gas analysis system (MultiGAS) instruments for in situ
measurements of SO2 , H2S , and CO2 concentrations in the gas plume and portable differential optical absorption spectrometer (MobileDOAS) instruments for spectroscopic
measurement of total SO2 emission rate, remotely controlled gas sampling in bags and sampling with gas denuders for posterior analysis on
the ground of isotopic composition and halogens. The platform we present was field-tested during three campaigns in Papua New Guinea: in 2016 at Tavurvur, Bagana and Ulawun volcanoes, in 2018
at Tavurvur and Langila volcanoes and in 2019 at Tavurvur and Manam volcanoes, as well as in Mt. Etna in Italy in 2017. This paper describes the drone platform and the multiple payloads, the various measurement strategies and an algorithm to correct for different
response times of MultiGAS sensors. Specifically, we emphasize the need for an adaptive flight path, together with live data transmission of a plume
tracer (such as SO2 concentration) to the ground station, to ensure optimal plume interception when operating beyond the visual line of
sight. We present results from a comprehensive plume characterization obtained during a field deployment at Manam volcano in May 2019. The Papua New
Guinea region, and particularly Manam volcano, has not been extensively studied for volcanic gases due to its remote location, inaccessible summit
region and high level of volcanic activity. We demonstrate that the combination of a multi-rotor drone with modular payloads is a versatile solution to
obtain the flux and composition of volcanic plumes, even for the case of a highly active volcano with a high-altitude plume such as
Manam. Drone-based measurements offer a valuable solution to volcano research and monitoring applications and provide an alternative and
complementary method to ground-based and direct sampling of volcanic gases.

/pdf/a-multi-purpose-multi-rotor-drone-system-for-long-range-and-ydl2bymqwv.pdf

A multi-purpose, multi-rotor drone system for long-range and high-altitude volcanic gas plume measurements

https://www.nature.com/articles/s41586-022-04981-x.pdf

Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland

Volcanic emissions are a critical pathway in Earth’s carbon cycle. Here, we show that aerial measurements of volcanic gases using unoccupied aerial systems (UAS) transform our ability to measure and monitor plumes remotely and to constrain global volatile fluxes from volcanoes. Combining multi-scale measurements from ground-based remote sensing, long-range aerial sampling, and satellites, we present comprehensive gas fluxes—3760 ± [600, 310] tons day−1 CO2 and 5150 ± [730, 340] tons day−1 SO2—for a strong yet previously uncharacterized volcanic emitter: Manam, Papua New Guinea. The CO2/ST ratio of 1.07 ± 0.06 suggests a modest slab sediment contribution to the sub-arc mantle. We find that aerial strategies reduce uncertainties associated with ground-based remote sensing of SO2 flux and enable near–real-time measurements of plume chemistry and carbon isotope composition. Our data emphasize the need to account for time averaging of temporal variability in volcanic gas emissions in global flux estimates.

/pdf/aerial-strategies-advance-volcanic-gas-measurements-at-280ktvy4kb.pdf

C. I. Schipper

Papers

Aerial strategies advance volcanic gas measurements at inaccessible, strongly degassing volcanoes