The study of production and depletion of chemical species is vital for the understanding of composition and evolution of planetary atmospheres. We present an implementation of photoinduced isotopic effects into the PATMO code (Ávila et al., 2021) code designed for the study of stable isotopes and photo-induced isotopic effects. With respect to the original code PATMO, where the photochemistry was not included, this report extends capability of the model to set photochemical processes for stable isotopes and thus enhancing its applicability. The PATMO code is flexible and allows the edition of new chemical reactions without need for hard code them. We also test how changes in spectral resolution affects the calculation of isotopic effects during the photodissociation of oxygen. We found that for a highly structured spectrum such as the Schumann-Runge band a spectral resolution larger than 0.005 nm is necessary for accurately modeling these isotopic effects. We also show that SO₂ and SO photodissociation couples in a complex shielding fashion and significantly affects the photo-induced isotopic effects. The model was also benchmarked against today’s Earth atmosphere, where the solar UV flux and the ozone profile of the US Standard atmosphere of 1976 was reproduced with the simple Chapman mechanism and improved with the implementation of NOx and HOx radicals.

To clarify the sources and fate of CH₄ enriched in coastal seawaters, we determined the distribution of both the concentrations and dual stable isotope compositions (δ¹³C and δ²H) of dissolved CH₄ in the bays of Ise and Mikawa in Japan during five sampling campaigns from 2013 to 2020, together with those in the major inflows of the Kiso, Nagara, and Yahagi Rivers. Excess CH₄ were found in the surface layer of Ise Bay, and their δ¹³C and δ²H values were close to those of CH₄ enriched in the major inflows, but deviated from those of CH₄ in the sedimentary layer at the bottom of Ise Bay. The oxidation rates of CH₄ in the water columns were negligibly small during the incubation experiments. In conclusion, the excess CH₄ in the surface layer of Ise Bay was derived from the inflows. The CH₄ enrichment in the freshwater sediments of the inflows showing up to four orders of magnitude higher CH₄ concentrations than those in the sediments of Ise Bay supported this conclusion. Similar results were obtained in Mikawa Bay. The total emission flux of CH₄ from the estuary area of Ise Bay was larger than the influx of CH₄ into Ise Bay via the inflows, suggesting that the CH₄ dissolved in the inflows was emitted into the atmosphere immediately after inflowing into the bay water.