What causes emissions in gas turbine combustors and how are they reduced?

Primary emissions include NOx (formed at high temperatures through Zeldovich mechanism), CO (incomplete combustion in cool zones), unburned hydrocarbons (UHC), and smoke/particulates. NOx increases with temperature and residence time; CO increases at low temperatures. Reduction strategies: Lean premixed combustion (lower peak temperatures, reduces NOx 50-80%), Rich-burn quick-quench lean-burn (RQL) staging, Twin-annular premixing swirler (TAPS) designs, Improved fuel-air mixing (reduces hot spots), and Optimized residence time. Modern LEAP and GEnx engines meet CAEP/8 standards with 50% NOx margin. Trade-offs exist between NOx (wants low temp) and CO/stability (want higher temp).