Water molecules comes in several varieties, of which H₂¹⁶O is the most common. These varieties behave differently enough under freezing to create strong changes in the ratio of heavy to light water molecules. Here we compare observations of these ratios from satellites and high-altitude airborne instruments. These observations provide information about how air reaches the upper parts of the atmosphere, so it is important to reconcile difference between different modes of observations.

Sulfur dioxide (SO₂) is a key precursor to aerosol formation, particularly in remote marine environments, ultimately affecting cloud properties and climate. Accurate quantification of atmospheric SO₂ is therefore crucial. This work compares a custom-built laser-based instrument to two commercial SO₂ analysers during measurements from a large research aircraft. Our results show that this custom-built system offers greater sensitivity at time resolutions required for aircraft measurements.