The Influence of Air Pollution in Mexico City
Mexico City is regarded as one of the densely polluted and populated metropolitan cities in the globe. Mexico City’s high altitude and the surrounding mountains have exacerbated the pollution predicament and this mainly emerges from the ozone. The rapidly expanding urban population combined with the problematic geographical setting of the city of Mexico are the main contributors of air pollution in the city of Mexico. Accordingly, the utilization of the fossil fuels in the elevated, tropical, mountainous basin also generates a considerable high level of pollution which exceeds the recommended standards of pollution. It is necessary to implement many strategies in order to control the high pollution rate in the city of Mexico. For example, such measures may entail introducing driving bans, expanding public transportation, utilization of alternative energy saving fuels, closing factories and relocating some industrial activities.
Geography of Mexico City
Mexico City is an area that generally has a high altitude and is surrounded by mountains that form a basin. During the early years of settlement, the elevated, mountain rimmed physical formation of most parts of the city were highly beneficial to its inhabitants. For instance, the lakes provided a means of transport, water and food; the local forests were a source of fuel and building materials, while the surrounding slopes supplied the natives with a variety of local foodstuffs and livestock. In addition, the climate of Mexico City, a highland location, was almost devoid of majority of the lowland tropical diseases. However, the physical environment of the Mexico City basin began to deteriorate after the city was occupied by Spaniards and the growing Mestizo population cut down the forests so as to obtain fuel and also building materials. Consequently, the natural lakes which were assets that were strongly associated with devastating floods as the Mexico City expanded rapidly (Collins & Scott, 1993).
Mexico City’s physical geography and topography contribute considerably to the usually high concentration of pollutants in the area. Collins and Scott (1993) state that the mountains to the north rise to elevations of about 3,000 metres while those to the south rise to elevations that reach about 3,500 metres. As a result, the valley bottom is relatively flat while the entire basin floor is estimated to range at between 2,200 and 2,300 metres above the sea level. The period between November and March usually experiences descending air combined with reduced movement of the upper air and consequently, this impedes the vertical mixing (Constanza, 2003). Additionally, the intense sunshine throughout the year when combined with this altitude and elevation reacts with the unburned hydrocarbons resulting in the formation of the ozone-rich smog. The winds usually penetrate the Mexico City basin through the north where the mountainous rim is at its lowest. It is no surprise therefore that the prevailing winds usually ferry pollutants such as the industrial smoke, particulates, dry human wastes and salt saturated lake bed sediments to the metropolitan area. In addition, these low level winds are usually too weak to continue pushing these pollutants from the basin (Baynham & Prieto, 1997).
The cool air then drains down the slopes of the city and it is attracted towards the city heat island and this consequently forms the recurrent temperature inversions. Another temperature inversion usually occurs at the same time at higher altitudes in which case the down slope winds normally ferry the polluted air from the basin back to the city and this regularly creates a distinctive diurnal pattern mainly from the air contamination. At 2,300 metres, the atmospheric pressure is usually reduced by almost 20 percent of its normal level and this means the area has less oxygen concentration available per every cubic metre of atmosphere. As a result, the efficiency of the fossil fuel combustion significantly reduces thus creating a huge amount of unburned hydrocarbons. The particulates in the air are consequently a by-product of unfinished fossil fuel combustion (Constanza, 2003). Accordingly, in this environment, the particles usually remain airborne for a very long period of time and this tends to increase the probability that such particles will bond with toxic substances in the air.
Causes of Air Pollution in Mexico City
The active interaction of physical factors in Mexico City form varied air pollutants which are particularly diverse in terms of their chemical characteristics and can include a wide range of components such as carbon monoxide, lead pollutants, sulphur and nitrogen oxide, ozone and particulates. Such pollutant components make up most of the photochemical cloud which hangs over the Mexico City where ozone is the main cause of air pollution. According to Baynham and Prieto (1997), ground level ozone usually forms when the carbon based chemical vapours or volatile organic compounds in air combine and react with nitrogen oxides mostly in the presence of strong sunlight. The vehicular exhausts and emissions from refineries in most cases produce most of the volatile organics elements. For example, nitrogen oxides are usually emitted during the process of fuel combustion within industries, automobiles and power plants. The ground level ozone usually forms out of the complex interaction between chemical vapours, oxides, and direct sunlight and consequently, it is usually not directly connected to a specific source. However, the ozone precursors are directly attributed to air pollution, in particular volatile organic compounds and nitrogen oxides.
The city of Mexico is home to more than 30,000 factories and also has more than four million motor vehicles. The vehicles and factories combined emit ozone precursors which in turn react with other elements given the presence of a strong sunlight hence causing the ground level ozone. Characteristically, ozone is normally considered as one of the warm-season challenges in large cities yet in Mexico City, the latitude and elevation of the city cause the ozone outbreaks to take place even in temperatures that are lower than 25 degrees Celsius (Sierra-Vargas & Teran, 2012). The ozone resulting from emissions from the factories and vehicles formulate the most prevalent and biologically active element in the photochemical smog in the basin of Mexico City. Due to the overall rise in the ozone, there has been spread of high ozone levels to almost all parts of the city area (Collins & Scott, 1993).
Suspended Particulates or Particle Matter
In most cases, suspended particulates are the main cause of most of the haze which shrouds and clouds the city of Mexico skyscrapers, the acidic brown rain and by this, that has even compelled the aircrafts to make use of instrument flight rules during daylight hours. According to Gutierrez and Kumar (2009), the materials causing the total suspended particulates encompass all the particles present in the atmosphere that measures less than 50 microns in diameter. The prolonged particulates suspension usually raises the chances that these particulates will bond with other toxic chemicals or biological agents in the air and thus be inhaled. Such particulates can occur naturally in wind-borne dust, soil particles and can also be created from other human activities.
The primary particulates are normally released into the atmosphere directly as a result of industrial processes and transportation activities. Nevertheless, the secondary particulates include aerosols which are produced when chemicals react with other atmospheric components. According to Constanza (2003), most of the suspended particulates above the city of Mexico are directly linked to the physical geography of the basin. The mountain-rimmed basin of the Mexico City plays a critical role in the formulation of temperature inversions which consequently concentrate the suspended particulate matter and hold it closer to the earth’s surface. The low settling velocity in the basin usually is the reason why the fine particles in the atmosphere remain suspended over a longer period hence producing a characteristic brown cloud (Riveros & Sandoval, 1998).
Effect of Air Pollution on Nature, Human Health and Environment
The effects of air pollution in Mexico City are mainly determined by the nature of the pollutant, concentration levels and exposure periods. Such pollution effects can usually range from mild irritation to severe sickness or premature death amongst inhabitants of the area. Ozone is a colourless gas which can be produced when unstable chemicals react with ultraviolet light. The build up of rather high concentrations of Ozone is a major atmospheric pollution problem in Mexico City. The main sources of ozone are normally the atmospheric reactions of hydrocarbons which are in most cases produced from the combustion engines and nitrogen oxides where there exists strong ultraviolet rays in sunlight (Constanza, 2003). Ozone has deadly effects on the growth of plants and people as it can cause irritated eyes, constant headaches and intensified hyper-reactivity. Hydro carbons that are emitted from incomplete combustion of fossil fuels are regarded as potent mutagens which can trigger cancer (Collins and Scott, 1993). When nitrogen oxides comes into contact with humid air or water aerosols, it reacts to form nitric acid. Inhalation of nitric acid usually exerts corrosive effects on the nasal mucus, the lungs trachea and alveolar tissues hence causing respiratory diseases.
Carbon Monoxide in Mexico City is formed as a result of the incomplete hydrocarbons combustion which can arise from internal combustion engines which burn fossil fuels, for instance gasoline and diesel. The main impact of Carbon Monoxide is that it produces Carboxyl-haemoglobin and this can combine with haemoglobin in the blood (Trivedi, 2011 P. 80). The result of this, is the prevention of oxygen in the human body from being transported from the lungs to target tissues. The particle matter and aerosols also result in many health and environmental impacts in Mexico City and the persistent haze blankets which engulf the city, especially during winter are usually formed from the particle matter and aerosols. These pollutants which are a combination of primary and secondary particle matter also significantly degrade the visibility of the city (Gutierrez & Kumar, 2009).
Efforts to Reduce the Impact of Air Pollution in Mexico
Mexico City has made major efforts towards minimizing air pollution and the related effects. The city’s transportation system was found to be the main source of pollution in the Metropolitan Area and hence, all the strategies aimed at reducing or controlling atmospheric pollution centered on transportation improvement programs. There are several programs which have been established to combat air pollution in Mexico City with the first program being the reduction of the use of private vehicles in the city so as to eliminate the emission from vehicles. To control this use of private vehicles in the city at given periods of time, the Mexican government has implemented a daily stop program when people are not permitted to use their cars. (Sierra-Vargas & Teran, 2012). These days are usually distributed randomly so as to encourage the private car owners to utilize the public transport or even embrace the concept of car-pooling. The implementation of the Urban Transportation System in Mexico City will considerably help to minimize the fossil fuelled vehicles fleet on the roads of the city hence effectively reduce the emission of ozone precursor elements (Baynham & Prieto, 1997).
The other program entails the process through which the conditions of the vehicle are controlled. The incomplete combustion engines in old and poorly maintained vehicles are usually the cause of the direct production of carbon monoxide gas and unburned hydrocarbon emissions which create part of the ozone precursors. As a result, the enforcement of engine maintenance standards in the city has been an important goal of the local government. For example, a key compulsory program that has been enforced by the authorities is the “verification program”(Riveros & Sandoval, 1998). The other program consists of changing the fuels to the use of more environmentally friendly sources of fuel. Most of the reformulated fuels sources have been tested in the Metropolitan city area with few transformations on the quality of the gasoline which have been accepted. This is because the current engine technology combined with the unfavourable meteorological and geographic features of Mexico City area has been the main cause of the high quantities of ozone precursor produced and not necessarily the fuel quality (Sierra-Vargas & Teran, 2012). In addition, to reduce the production of high levels of ozone precursors, the government has also implemented programs with the aim of reducing the levels of ozone precursors emitted. For example, these programs include lowering the amounts of lead and sulphur in fuels and the compulsory utilization and implementation of catalytic converters in engines.
Air pollution currently affects millions of people in Mexico City which is ranked as one of the most polluted and populated metropolitan cities in the World. The high altitude of Mexico City and the surrounding mountains exacerbate the pollution challenge mainly because of the ozone. Air pollution in the city of Mexico has come about as a result of the effects of the rapidly expanding urban population combined with the problematic geographical setting of the city of Mexico. In order to control the high pollution rates, many control strategies must be implemented and these may include introduction of driving bans, expansion of public transportation, utilization of alternative fuels, closure of the pollutant factories and undertaking industrial relocations.
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Gutierrez, E., Foster, A. & Kumar, N. (2009). Voluntary Compliance, Pollution Levels, and Infant Mortality in Mexico. The American Economic Review, 99(2), 191-197.
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