Trends in exhaust emissions from in-use Mexico City vehicles, 2000-2006. A remote sensing study.

A remote sensing study was conducted in year 2006 in four locations of the Metropolitan Area of Mexico City (MAMC). Two of the sites were the same studied back by us in year 2000 and by others in year 1994. A database was compiled containing 11,289 valid measurements for the carbon monoxide (CO), total hydrocarbons (THC), and nitric oxide (NO) exhaust vehicles emissions. Valid measurements were binned for each pollutant by the vehicle specific power (between -5 and 20 kW tonne(-1)) for the 2000 and 2006 databases. The mean average CO, THC, and NO emissions for year 2006 were determined to be 1.10 +/- 0.18 vol.%, 299 +/- 88.4 ppm, and 610 +/- 115.0 ppm, respectively. Matching the vehicle driving patterns of the fleet measured in year 2000 with the emissions factors obtained in this work, allows estimating the trends in the exhaust emissions of vehicles in the MAMC. The adjusted results of the remote sensing study performed in year 2006 shows that the fleet has decrease 22% in CO and 17% in NO emissions, with small change in total hydrocarbons emissions. The improvements could be related with the introduction in year 2001 of vehicles that met tighter emissions standards, particularly for nitrogen oxides.