VOLCANO WATCH: What is this new smell?

In this time of gratitude, residents and visitors to the island of Hawaii may be grateful for the return of good air quality, usually free of volcanic pollution.

Since the sharp drop in volcanic activity and gas emissions at Kīlauea in early August 2018, the air quality of the island has improved considerably. The rest of the state can also console itself with low levels of volcanic gas, as the southerly winds in winter will have much less volcanic pollution to blow along the chain of islands.

Sulfur dioxide (SO2) is the main contributor to the formation of volcanic air pollution, or vog, on the Kīlauea volcano. Since SO2 is released when the magma is shallow (less than 1 kilometer below the surface), the current lack of activity means that Kīlauea releases only a small amount of this familiar gas.

Currently, less than 200 tons of SO2 are emitted by the volcano every day. This is more than 20 times less than the average emissions during the 10 years of lava lake activity in Halema'uma'u and at least 200 times less than the peak of emissions during the eruption of the Zone of rift is less than 2018.

With these much lower emissions, many people were surprised that a strong, slightly unknown odor could be detected from Kīlauea by certain wind conditions. A change in the chemistry of the emitted sulfur gases is responsible for this new aroma.

A small amount of hydrogen sulphide gas (H2S), the smelly cousin of SO2, is being produced. With the current volcanic conditions, deeper magma has led to lower ventilation temperatures. Without shallow magma to evaporate groundwater, the environment beneath the surface is also much moister.

These colder and wetter conditions result in the formation of a small amount of H2S, in addition to SO2. The H2S is most commonly detected during interruptions of the trade winds and in the downwind locations of the Kīlauea summit, Pu'u'Ō'ō, and the rift zone crack system is below 2018. .

Sulfur dioxide gas, which produces a pungent aroma similar to that emitted during fireworks or kitchen matches, is noticeable by most people at a concentration of 0.3 to 1 part per minute. million (ppm) – 0.3 to 1 part gas per million parts of air. In some sensitive asthmatics, changes in lung function have been observed with SO2 concentrations as low as 0.1 ppm, well below the level detected by most human noses.

On the other hand, people can usually smell the smell of rotting H2S egg at lower concentrations ranging from 0.0005 to 0.3 ppm. H2S is present in Kīlauea in minute quantities, but this small detail can be quite noticeable.

The smell of H2S is a familiar scent for residents of hot springs or geothermal areas. It is also produced by the decomposition of organic matter (anaerobic digestion) and is released by sewers and wetlands. Even the human body produces a small amount of H2S.

The state of Hawaii has set a "nuisance level" for H2S at 0.025 ppm, based on the odor threshold. Negative symptoms of H2S exposure occur only when the concentrations are well above the olfactory threshold.

According to OSHA, prolonged exposure to 2-5 ppm may cause headaches, eye irritation, nausea, or breathing problems in some asthmatics. Concentrations measured in populated areas around Kīlauea are less than 1 ppm.

Although humans can detect H2S at very low concentrations, their sense of smell is lost at high concentrations. For example, exposure for two to five minutes at 100 ppm can cause sensory adaptation called "olfactory fatigue". However, H2S concentrations measured at Kīlauea, even directly at volcanic vents, are well below this level.

For those of us who have spent decades living with the familiar aroma of the "classic" vog, the introduction of the smelly H2S can be curious, even disconcerting. In the next chapter of the Kīlauea volcano activity, when the magma returns to the surface, we can expect a decrease in H2S emissions and a return to the more familiar smell of SO2 and particulate dominated vog. .