A variety of natural causes have forced the poor air quality upon Mexico city. One of the primary causes of this problem is the placement of Mexico city. First of all, Mexico city's Latitude is 18° North. This means that it is very close to the equator, and receives much more sunlight than most of the world. Adding onto the problem, is the high altitude of Mexico City. Mexico City is situated in a valley between a variety of mountains. The mountains' average height is 2240m above sea level. Due to it being located between such high mountains, and also so close to the equator, Mexico City tends to receive much more sunlight than the rest of the world, and at a greater intensity also. In general, sunlight tends to cause various compounds to fuse together with heat and form ozone, a toxic gas that contributes heavily towards air pollution. This gas harms humans directly when enhaled at ground level.
Figure 2.1: the process which sunlight will go through to form ozone, a gas which contributes to air pollution. The sunlight comes in contact with the nitrogen oxides and the volatile organic compounds released by emissions in automobiles within the city "bake" together forming toxic ozone gas.
Source: http://www.epa.gov/climatechange/impacts-adaptation/health.html
Another geographical issue causing the extreme air pollution is the fact that Mexico City is a city built in a crater of an extinct volcano. Because of this, the surrounding land-forms provide a natural windbreak preventing the dispersion of the pollutants that blanket over the city. These neighboring hills creating a pollutant trapping valley causing the pollution to become thicker and thicker, often becoming the thick smog which can be seen covering Mexico City.
Figure 2.2: This is a birds eye view picture of Mexico City, comparing the pollution on April 8, 2001 to December 5, 2001. Notice how under the clouds there is a visible layer os smog which seems to cover the city. This image shows how the pollution is trapped over Mexico City unable to disperse.
Source: Mario & Luisa Molina " Mexico Air Quality Case Study" Slide 4 www.iuappa.com/seminar/Molina1.ppt Mexico City, is not only built on a volcanic landmark, however is also surrounded by active volcanoes. On January 7th 2015 "Popocatepetl" an active volcano located close to Mexico City erupted smothering the city in volcanic ashes causing mass asthmatic breakout among the public.
ALTITUDE ANd THe AIRAltitude is a major factor of the degrading quality of the air in Mexico City. Mexico City, because of its high altitude (2240m approx.), has a lesser concentration of oxygen in its atmosphere. Hydrocarbons such as methane (common fuel used in cars) need sufficient oxygen to produce neutral gases (carbon dioxide). The burning or combustion of such fossil fuels in insufficient oxygen leads to the production of harmful polarised gases (carbon monoxide). Also, because of its altitude there are frequent thermal inversions in the atmosphere and further trap the pollutants at ground level by suppressing the convection. Thermal Inversion is the reversal of the normal decrease of temperature with the altitude. The pollutants, because were never circumvented, could freely be inhaled by any person living in Mexico City.
Figure 2.3: This generally shows how smog is 'capped' and not circulated outwards into the outer atmosphere. Thermal inversion occurs in places with high altitudes and causes either a rise or drop in temperature. Because of this rise and drop of temperature, convection currents cannot flow thus trapping the pollutants within the valley. In this image you can see how the thermal inversion is capping the pollutants creating a "blanket" over the city.
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