Evolution of anthropogenic pollution at the top of the regional mixed layer in the central Mexico plateau
At night, the mass fraction of sulfate went up by a factor of ten from the daytime value when air arrived from the east. The relationship between the CO and OM suggests that the majority of the daytime OM is from biomass burning and at night it is from wood burning.
Whereas the maximum CO at Altzomoni, 0.35 ppm, was approximately one tenth of the CO measured at the same time in the center of Mexico City, the maximum O3 of 120 ppb was approximately the same as in the city. The maximum nighttime values of O3 was 60 ppb, indicating the presence of residual pollution.
From these results we conclude that even though Mexico City is the second most populated city in the world, with an associated high level of pollution, there are other significant sources of pollution in Mexico that contribute to the mixture of emissions that are dispersed throughout the region. This mixture rapidly erases the signature of a unique Mexico City “plume” and suggests that the environmental impact of this region should be considered as one that stems from a large area source rather than a single megacity.