Polluted Outdoor Air:

• pollen, dust, fungal spores
• industrial emissions
• vehicle emissions

Nearby Sources:

• loading docks
• vehicle parking or loading
• odours from dumpsters
• unsanitary debris or building exhausts near outdoor air intakes

Underground Sources:

• radon
• pesticides
• leakage from underground storage tanks
• soil gases

HVAC Equipment:

• microorganisms growing in drip pans, ductwork, coils, and humidifiers
• improper venting of combustion products
• dust , debris or fibres in or from ducts or duct linings
• plumbing traps or sumps

Non-HVAC Equipment:

• emissions from office equipment (volatile organic compounds, ozone)
• emissions from shops, labs, cleaning processes
• custodial practices
• atria, planters, and other wet areas

Components:

• microorganisms growing on soiled or water-damaged materials
• dry traps that allow the passage of sewer gas
• materials containing
  volatile organic compounds, inorganic compounds, or damaged asbestos
• materials that produce particles (dust) or fibres
• tunnels, basements and crawlspaces
• exposed soil (walls/floors)

Furnishings/Finishings:

• emissions from new furnishings, flooring, or textiles
• microogranisms growing on or in soiled or water-damaged furnishings

• science laboratories
• vocational arts areas
• copy/print areas
• food preparation/eating
  areas
• smoking lounges
• cleaning materials
• emissions from trash
• pesticides
• odours and volatile organic compounds from paint, sealants
  or adhesives
• occupants with communicable diseases
• markers and felt pens
• insects and other pests
• personal care products
• animals
• classroom materials or material storage
• renovation activities