Respiratory aerosols from breathing and talking are an important transmission route for viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Previous studies have found that particles with diameters ranging from 10 nm to 145 μm are produced from different regions in the respiratory system and especially smaller particles can remain airborne for long periods while carrying viral RNA. We present the first study in which respiratory aerosols have been simultaneously measured with carbon dioxide (CO₂) to establish the correlation between the two concentrations. CO₂ concentrations are easily available through low-cost sensors and could be used to estimate viral exposure through this correlation, whereas source-specific aerosol measurements are complicated and not possible with low-cost sensors. The increase in both respiratory aerosols and CO₂ was linear over ten minutes in a 2 ${\mathrm{m}}^3$ chamber for all participants, suggesting a strong correlation. On average, talking released more particles than breathing, with 14,600 ± 16,800 min⁻¹ (one-$\sigma$ standard deviation) and 6210 ± 5630 min⁻¹ on average, respectively, while CO₂ increased with 139 ± 33 ppm min⁻¹ during talking and 143 ± 29 ppm min⁻¹ during breathing. Assuming a typical viral load of $7\times {10}^6$ RNA copies per mL of oral fluid, ten minutes of talking and breathing are estimated to produce 1 and 16 suspended RNA copies, respectively, correlating to a CO₂ concentration of around 1800 ppm in a 2 ${\mathrm{m}}^3$ chamber. However, viral loads can vary by several orders of magnitude depending on the stage of the disease and the individual. It was therefore concluded that, by measuring CO₂ concentrations, only the number and volume concentrations of released particles can be estimated with reasonable certainty, while the number of suspended RNA copies cannot.

Respiratory Aerosols from breathing and talking have found wide acceptance as a transmission route for viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Previous studies have found particles with diameters ranging from 10 nm to 145 µm, exhibited from different regions in the respiratory system. We present the first chamber study, in which respiratory aerosols have been simultaneously measured with carbon dioxide (CO2) to establish the correlation between the two concentrations. CO2 concentrations are easily available through low-cost sensors and could be used to estimate viral exposure through this correlation, whereas source-specific aerosol measurements are complicated and not possible with low cost sensors. The increase in both PM10 and CO2 was linear over ten minutes in a 2 m3 chamber for all participants, suggesting a strong correlation. On average, talking released more particles than breathing, with 14,600 ± 16,800 min-1 (one-σ standard deviation) and 6,210 ± 5,630 min-1 on average, respectively, while CO2 increased with 139 ± 33 ppm min-1 during talking and 143 ± 29 ppm min-1 during breathing. Assuming a typical viral load of 7 × 106 RNA copies per ml of oral fluid, ten minutes of talking and breathing are estimated to produce 7 and 16 suspended RNA copies, respectively, correlating to a CO2 concentration of around 1.800 ppm in a 2 m3 chamber. This provides a strong argument for keeping indoor spaces well ventilated and shows how CO2 concentrations, measured with low-cost sensors, could be used as a proxy for viral exposure.

Dating the bottommost section of an ice core is often complicated by strong layer thinning and possible disturbances in the stratigraphy. The radioactive decay of atmospherically produced ³⁶Cl and ¹⁰Be can provide age estimates, where traditional methods can no longer be used. In this study, we investigated ice from the bottom of the Skytrain ice core, which was drilled in West Antarctica next to the Ronne Ice Shelf and has previously been dated to 126 kyr BP about 24 m above bedrock. Apart from decay, radionuclide concentrations in ice can be influenced by production rate variations, atmospheric transport and deposition variations, and, at low accumulations sites, by chlorine loss through hydrogen chloride outgassing. Using the ³⁶Cl $/$ ¹⁰Be ratio largely removes production related variations and we were able to confirm that no ³⁶Cl loss occurs at Skytrain Ice Rise, as the nuclear weapon test caused peak in ³⁶Cl concentrations was found at the expected depth corresponding to the 1950s and 1960s. An analysis of samples with known age showed that individual radionuclide concentrations and the ³⁶Cl $/$ ¹⁰Be ratio are negatively correlated to the δ¹⁸O signal, which was used to apply a climate correction that enabled a higher precision for age estimates of previously undated samples by reducing the uncertainty of the initial ratio from 14 % to 9 %. The deepest analysed section of the Skytrain ice core was found to be 561${}_{-\mathrm{109}}^{+\mathrm{110}}$ kyr old.

The 36Cl/10Be ratio has the potential to be a dating tool for old ice, as it decays with a combined half-life of years and is thought to be independent of production changes, which affect the individual radionuclide concentrations in ice cores. However, when EDC samples with various ages between the Holocene and 887 kyr BP were analysed, the 36Cl/10Be ratio was found to vary significantly between samples instead of decaying smoothly over time. Due to the different physical and chemical properties of 36Cl and 10Be, different sensitivities to changes in climatic parameters, such as tropopause pressure and precipitation, are potentially the cause of the observed variability. Additionally, chlorine can be lost at low accumulation sites, such as EDC, as it can turn into hydrogen chloride and gas out from the firn. We present new measurements of the 36Cl/10Be ratio from the Skytrain ice core, which should be unaffected by chlorine loss, due to the higher accumulation rate at its drilling site. The measurement series extends below the dated sections of the ice core to test the decay dating and help extend the Skytrain age scale. To analyse differences in transport and deposition between radionuclides, the 36Cl/10Be ratio will also be determined with annual resolution in samples from 1982 – 2013 and compared to several climate parameters of the NOAA/CIRES/DOE 20th century reanalysis (V3) dataset. However, the data of this project are not yet available.

Dating the bottommost section of an ice core is often complicated by strong layer thinning and possible disturbances in the stratigraphy. The radioactive decay of atmospherically produced ³⁶Cl and ¹⁰Be can provide age estimates, where traditional methods can no longer be used. In this study, we investigated ice from the bottom of the Skytrain ice core, which was drilled in West Antarctica next to the Ronne Ice Shelf and has previously been dated to 126 kyr BP about 24 m above bedrock. Apart from decay, radionuclide concentrations in ice can be influenced by production rate variations, atmospheric transport and deposition variations, and, at low accumulations sites, by chlorine loss through hydrogen chloride outgassing. Using the ³⁶Cl/¹⁰Be ratio largely removes production related variations and we were able to confirm that no ³⁶Cl loss occurs at Skytrain Ice Rise, as the nuclear weapon test caused peak in ³⁶Cl concentrations was found at the expected depth corresponding to the 1950s and 60s. An analysis of samples with known age showed that individual radionuclide concentrations and the ³⁶Cl/¹⁰Be ratio are negatively correlated to the δ¹⁸O signal, which was used to apply a climate correction that enabled a higher precision for age estimates of previously undated samples. The deepest analysed section of the Skytrain ice core was found to be 552 ± 112 kyr old.