The Main Pollutants

Pollutant	Main sources	Effect
Particulate matter (PM10, PM2.5)	Combustion, cutting, handling, traffic	Respiratory and cardiovascular disease; fine fractions penetrate deepest
Oxides of nitrogen (NOx)	Any high-temperature combustion	Respiratory irritation; forms ground-level ozone and secondary particulates
Sulphur dioxide	Combustion of sulphur-containing fuels	Respiratory effects; acid deposition
Carbon monoxide	Incomplete combustion	Acute toxicity
Volatile organic compounds	Solvents, coatings, printing, fuel handling	Ozone formation; some toxic or carcinogenic
Ammonia	Agriculture, some processes, refrigeration leaks	Secondary particulate formation; nitrogen deposition
Heavy metals and dioxins	Combustion of contaminated materials, smelting	Persistent, accumulative, highly toxic
Greenhouse gases	Combustion; refrigerant and process gas leaks	Climate change

Refrigerants

Fluorinated refrigerant gases have global warming potentials hundreds to thousands of times that of carbon dioxide, so a small leak can dominate a site's greenhouse gas footprint. They are subject to specific leak checking, record-keeping and technician certification requirements in most jurisdictions, and leaking systems are common because a system that still cools does not appear to be faulty.