The absorption spectra of H2S from 2000 to 11 147 cm−1 have been obtained with spectral resolutions of 0.006, 0.012, and 0.021 cm−1 using the Fourier transform spectrometer at Kitt Peak National Observatory. The transitions of 21 bands have been assigned for the first time and 9 others reanalyzed so that accurate energy levels, band origins, and rotational parameters could be determined. The analysis of these data revealed some remarkable features in the energy spectrum, e.g., fourfold clustering of rotational levels belonging to the symmetric and asymmetric components of local mode manifolds at a high degree of stretching excitation. This paper reports fitted vibrational parameters and predicted band origins of H232S up to 12 735 cm−1. It also presents the degenerate rotational constants and upper state energies of (301)–(202) and (311)–(212) at 1 μm as illustrations of clustering in the local mode limit.

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The COVID-19 global pandemic and associated government lockdowns dramatically altered human activity, providing a window into how changes in individual behavior, enacted en masse, impact atmospheric composition. The resulting reductions in anthropogenic activity represent an unprecedented event that yields a glimpse into a future where emissions to the atmosphere are reduced. Furthermore, the abrupt reduction in emissions during the lockdown periods led to clearly observable changes in atmospheric composition, which provide direct insight into feedbacks between the Earth system and human activity. While air pollutants and greenhouse gases share many common anthropogenic sources, there is a sharp difference in the response of their atmospheric concentrations to COVID-19 emissions changes, due in large part to their different lifetimes. Here, we discuss several key takeaways from modeling and observational studies. First, despite dramatic declines in mobility and associated vehicular emissions, the atmospheric growth rates of greenhouse gases were not slowed, in part due to decreased ocean uptake of CO2 and a likely increase in CH4 lifetime from reduced NOx emissions. Second, the response of O3 to decreased NOx emissions showed significant spatial and temporal variability, due to differing chemical regimes around the world. Finally, the overall response of atmospheric composition to emissions changes is heavily modulated by factors including carbon-cycle feedbacks to CH4 and CO2, background pollutant levels, the timing and location of emissions changes, and climate feedbacks on air quality, such as wildfires and the ozone climate penalty.

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The presence of a stratospheric haze layer may produce increases in both the actinic flux and the irradiance below this layer. Such haze layers result from the injection of aerosol-forming material into the stratosphere byvolcanic eruptions. Simple heuristic arguments show that the increase in flux below the haze layer, relative to a clear sky case, is a consequence of "photon trapping. Consider a stratospheric H2SO4 aerosol layer formed by a volcanic eruption. This can be modeled as a nearly conservatively scattering layer in a Rayleigh-scattering atmosphere (layer B in Figure 1). Intuition suggests that the introduction of the scattering would lead to an increase in the actinic flux above the aerosol layer (region A in Figure 1) due to back scattering, or within the aerosol layer (region B) due to multiple scattering. However, we might not expect increases in the actinic flux beneath the aerosol layer (region C), for the following reasons. In region C there is additional actinic flux due to multiple scattering by the aerosol layer B, but we can argue that this flux is originally in the direct solar beam. It has been removed by layer B, which redistributes the radiation into the backward direction (region A) and the forward direction (region C). Therefore it follows that the sum of the attenuated direct solar flux and the diffuse actinic flux in region C should not exceed the original actinic flux when the aerosol layer is absent. We might also anticipate that the absolute value of the irradiance would decrease at the surface with the introduction of the aerosol layer, reflecting the loss to space of backscattered photons. (In this paper, variation of the irradiance or its components will be discussed always with regard to absolute values.)We will show, however, that under certain circumstances the actinic flux below the aerosol layer can increase without violating conservation of photons and under special conditions the irradiance also can increase below the aerosol layer, with respect to the clear sky situation. Our new radiative transfer model is described and utilized to explore the effects of aerosols.