Evaluation of vehicle emission inventories for carbon monoxide and nitrogen oxides for Bogotá, Buenos Aires, Santiago, and São Paulo

We use concurrent morning peak observations of carbon monoxide (CO) and nitrogen oxides (NOx) to evaluate mobile emissions estimates for CO and NOx at Bogotá (Colombia), Buenos Aires (Argentina), Santiago (Chile) and São Paulo (Brazil). In all cities, molar ratios of CO to NOx decrease over the last 10–15 years. These ratios are not captured by available inventories. Comparison among inventories suggests that major uncertainties are linked to inadequate emission factors for CO and inadequate activity data for NOx. These results, in combination with previous studies, suggest that current NOx emissions are overestimated by a factor of up to 3 in Santiago and São Paulo, and Buenos Aires shows a slight overestimate by 20%. In the case of Bogotá we suspect that the current CO emission inventory is overestimated. Available observations provide valuable information, as exemplified hereby, but more careful attention must be paid to calibration and continuity of the stations.

► We use observed CO to NOx molar ratios to evaluate mobile emissions at four South American cities. ► CO to NOx molar ratios decrease over the last 10–15 years, mostly due to reductions in CO emissions. ▶ The observed ratios are not captured by available inventories. ▶ Major uncertainties are linked to CO emission factors and inadequate activity data for NOx. ▶ The evidence indicates overestimates of current NOx emissions.