Biodiversity monitoring at the community scale is a critical element of assessing and studying species distributions, ecology, diversity, and movements, and it is key to understanding and tracking environmental and anthropogenic effects on natural ecosystems.1, 2, 3, 4 Vertebrates in terrestrial ecosystems are experiencing extinctions and declines in both population numbers and sizes due to increasing threats from human activities and environmental change.5, 6, 7, 8 Terrestrial vertebrate monitoring using existing methods is generally costly and laborious, and although environmental DNA (eDNA) is becoming the tool of choice to assess biodiversity, few sample types effectively capture terrestrial vertebrate diversity. We hypothesized that eDNA captured from air could allow straightforward collection and characterization of terrestrial vertebrate communities. We filtered air at three localities in the Copenhagen Zoo: a stable, outside between the outdoor enclosures, and in the Rainforest House. Through metabarcoding of airborne eDNA, we detected 49 vertebrate species spanning 26 orders and 37 families: 30 mammal, 13 bird, 4 fish, 1 amphibian, and 1 reptile species. These spanned animals kept at the zoo, species occurring in the zoo surroundings, and species used as feed in the zoo. The detected species comprise a range of taxonomic orders and families, sizes, behaviors, and abundances. We found shorter distance to the air sampling device and higher animal biomass to increase the probability of detection. We hereby show that airborne eDNA can offer a fundamentally new way of studying and monitoring terrestrial communities.

Distributions of sulfur isotopes in geological samples would provide a record of atmospheric composition if the mechanism producing the isotope effects could be described quantitatively. We determined the UV absorption spectra of ³² SO ₂ , ³³ SO ₂ , and ³⁴ SO ₂ and use them to interpret the geological record. The calculated isotopic fractionation factors for SO ₂ photolysis give mass independent distributions that are highly sensitive to the atmospheric concentrations of O ₂ , O ₃ , CO ₂ , H ₂ O, CS ₂ , NH ₃ , N ₂ O, H ₂ S, OCS, and SO ₂ itself. Various UV-shielding scenarios are considered and we conclude that the negative Δ ³³ S observed in the Archean sulfate deposits can only be explained by OCS shielding. Of relevant Archean gases, OCS has the unique ability to prevent SO ₂ photolysis by sunlight at λ >202 nm. Scenarios run using a photochemical box model show that ppm levels of OCS will accumulate in a CO-rich, reducing Archean atmosphere. The radiative forcing, due to this level of OCS, is able to resolve the faint young sun paradox. Further, the decline of atmospheric OCS may have caused the late Archean glaciation.

The heterogeneous oxidation of SO₂ by NO₂ on mineral dust was studied using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and a Knudsen cell. This made it possible to characterise, kinetically, both the formation of sulfate and nitrate as surface products and the gas phase loss of the reactive species. The gas phase loss rate was determined to be first order in both SO₂ and NO₂. From the DRIFTS experiment the uptake coefficient, g, for the formation of sulfate was determined to be of the order of 10^-10 using the BET area as the reactive surface area. No significant formation of sulfate was seen in the absence of NO₂. The Knudsen cell study gave uptake coefficients of the order of 10^-6 and 10^-7 for SO₂ and NO₂ respectively. There was no significant difference in uptake when SO₂ or NO₂ were introduced individually compared to experiments in which SO₂ and NO₂ were present at the same time.