A stack (or smokestack) is a tall vertical structure used to discharge exhaust gases from industrial processes, power generation, or heating systems into the atmosphere. Stack height helps disperse emissions and reduces ground-level pollution concentrations. Industrial facilities, power plants, and large buildings use stacks to vent combustion gases. Environmental regulations govern stack emissions, requiring permits, monitoring, and pollution control equipment for significant emission sources. Stack testing measures actual emissions to verify compliance with air quality standards. Emission limits vary by pollutant type, facility size, and location. Provincial environment ministries regulate stack emissions as part of air quality management programs.