sulfurous

Sulfurous is an adjective relating to sulfur, the chemical element. It is used to describe materials, fumes, and odors associated with sulfur compounds, especially the characteristic rotten-egg smell from hydrogen sulfide or sulfur dioxide. The term can also evoke brimstone imagery found in literature and religious texts.

In chemistry, sulfurous indicates species in which sulfur has an oxidation state of +4. Examples include sulfurous acid (H2SO3) and the gaseous oxide sulfur dioxide (SO2). The term is often contrasted with sulfuric, which refers to sulfur in the +6 oxidation state, as in sulfuric acid (H2SO4).

Spelling variants reflect regional usage: sulphur and sulphurous are common in British English, while sulfur and sulfurous are typical in American English. The meanings are otherwise the same.

Environmental and industrial contexts frequently use sulfurous to describe emissions of sulfur dioxide from fossil fuel combustion, volcanic gases, or geothermal sources. Exposure to high concentrations of sulfur dioxide or hydrogen sulfide is hazardous and can irritate the respiratory system; long-term exposure to sulfur compounds also contributes to environmental issues such as acid rain.