Air emissions: principal industrial source of hydrogen sulfide (H2S): Among the following, which industry is the most prominent source of H2S emissions to air under typical operating scenarios?

Introduction / Context:
Hydrogen sulfide (H2S) is a toxic, corrosive gas with a characteristic rotten-egg odour. Recognizing its main industrial sources is essential for emission control, monitoring, and community odor management.

Given Data / Assumptions:

• Industries listed represent common heavy emitters of combustion or process gases.
• We consider routine operations and known by-product streams.
• We focus on H2S formation or release pathways, not SO2 alone.

Concept / Approach:
Refineries and gas processing handle sulfur-bearing crude oils and gases. H2S is generated during hydrotreating, hydrocracking, and in sour gas streams; it is routed to amine systems and then to sulfur recovery units (Claus process). Any upsets, leaks, or flaring can release H2S. By contrast, coal power primarily emits SO2 post-combustion; pulp/paper (kraft) does emit reduced sulfur compounds, but refineries remain the archetypal large-scale H2S source; metallurgical smelting typically oxidizes sulfides to SO2, not H2S.

Step-by-Step Solution:
Identify industry with direct H2S-rich process streams: petroleum refining.Note control systems: amine sweetening → Claus sulfur plant; emissions can occur during upsets/maintenance.Therefore, the most prominent H2S source among the choices is “Petroleum refineries”.

Verification / Alternative check:
Process flow diagrams for refineries show multiple H2S generation points; environmental permits emphasize H2S/total reduced sulfur monitoring around these facilities.

Why Other Options Are Wrong:
Coal power: primarily SO2, not significant direct H2S in stacks.Pulp and paper: does emit TRS (including H2S), but scale and prevalence make refineries the more typical dominant source.Smelters: oxidize metal sulfides to SO2; H2S is not the main emitted species.Cement plants: dust and NOx/SO2 are typical, not H2S.

Common Pitfalls:
Confusing SO2 and H2S. They are related sulfur species but originate and are controlled differently.

Final Answer:
Petroleum refineries