Real-World Emission Factors for Andean Light-Duty Vehicles Based on a PSVm10-Validated Driving Cycle Across 0–4000 m Altitude

Emission inventories for high-altitude Andean cities rely on sea-level certification cycles that misrepresent real-world combustion conditions. This study derives altitude-resolved emission factors (EFs) for light-duty gasoline vehicles across 0–4000 m a.s.l. in Ecuador using the purpose-built Andean Ecuador Driving Cycle (aedc), validated against naturalistic data via the Percentile Speed Vector metric (PSVm10; IGS =1.89 vs. IGS =2.30 for the WLTC). Ten vehicles (Euro III–V) were instrumented with OBD-II and portable analysers recording CO, NO, HC, and CO2 at 1 Hz over a four-year campaign (2021–2025; ≈2000 h). K-Means clustering on PSVm10 identified five operating regimes (silhouette ≈0.384). Under dynamically equivalent aedc conditions, NO, CO, and HC all peaked in the 1000–2000 m band (NO: 0.188gkm−1, 6.7× the sea-level value; CO: 4.47gkm−1, +50%; HC: 0.047gkm−1, +292%), fell in the 2000–3000 m band, and partially rebounded above 3000 m (NO: 0.186gkm−1); CO2 instead declined monotonically with altitude (182 to 119gkm−1, −35%), tracking a near-stable-to-slightly-declining fuel consumption (8.56 to 8.11L/100km) consistent with reduced aerodynamic drag at altitude partially offsetting the density penalty. These results show that altitude affects pollutants through distinct, non-monotonic mechanisms rather than a uniform trend, so that single-coefficient altitude corrections introduce systematic bias in Andean emission inventories.