The Development of Air Pollution in Mexico City

Abstract

The present essay documents changes to both objects of inquiry and the meaning of the epistemological concept of air pollution and it explains the processes that produced them. Smog as a result of production processes and the use of the automobile was not a concern for researchers and government managers in Mexico City, who were used to the dust storms resulting from the desiccation of the great Texcoco Lake during much of the 20th century, until the most industrialized nations of the West and the World Health Organization (WHO), alongside other international bodies such as the Organization for European Economic Cooperation (OEEC), reframed what was understood as air pollution, between the end of the 1960s and the beginning of the 1970s. Concerns about dust storms were displaced by concerns about factory and automotive emissions that contained new dangers—invisible hazards, just then being estimated, which altered what was understood or considered air pollution and gave rise to the quantification of particulate matter (which was then known as suspended dust particles) and new practices such as atmospheric monitoring. This essay concludes that what is understood as air pollution is situated; its meaning is not finite but simply evolves with time and with the rise of new global risks and concerns.

Introduction

Although nowadays most people relate air pollution with industrial emissions and automotive exhaust-pipes, the notion of pollution goes back thousands of years; we can find it in every human culture (Glacken, 1967; Thorsheim, 2016; Trumble & Finch, 2019). However, that which is considered pollution in a given cultural and historical context does not correspond to what may be classified as such in another (Douglas, 1985).

To underline how in the span of a few years the risk, then, came to be embodied in a set of chemical substances considered to be the most common and hazardous to human health, first I will briefly describe the episode known as the Great Smog of London. I do so not merely because it is the best-known case of air pollution’s catastrophic consequences but also because of the impact of this event on defining which science would need to be developed to control the phenomena of pollution. After the Great Smog of London—and other similar air pollution crises in highly industrialized countries—there could be no doubt regarding the dangers of breathing polluted air (Bell et al., 2004). Air pollution’s conceptual spectrum was simultaneously colonized.

Second, I will explain the particular origin of Mexican dust storms, the damages they caused, and their general characteristics, aiming to review what scientists and public officials considered air pollution before and after these international entities defined new objects of study, methods, and measuring instruments to quantify air pollution. With this in mind, I mention, on the one hand, two of the studies carried out by the Public Health and Tropical Diseases Institute where they analyzed the biological content of dust storms, given their interest in the fungi and microorganisms that are sometimes transported through them and, because of that they may sicken the population. And, on the other hand, I will also discuss the studies carried out by both the Ministry of Public Health and Assistance and the National Autonomous University of Mexico regarding the phenomenon of air pollution, at the time attention began to shift to the set of substances or pollutants that were thought to be more common and dangerous to human health (among them, suspended dust particles and sulfur dioxide). These emerging studies shifted the focus from a medical-bacteriological one to a perspective more centered on chemistry and engineering. The consequence was a change in what was considered air pollution. Thus, in 1967, the Mexican government joined the measurement program of the World Health Organization (WHO). This is the antecedent of the current atmospheric monitoring practices in Mexico City.

Pollution has been conceived in more than one way, even in a single context (Polajnar et al., 2014). As I argue in this article, scientific entities that articulate scientific knowledge and practice are local and vary over time (Haraway, 2001). So, in this essay, I will assess the kinds of losses and transformations implied by the shift from one notion of pollution to another and show the origins of the measurement of particulate material, so it is located in the recent past and in a specific context. The theoretical framework of this essay is based on cultural studies on science and technology as well as in environmental history. The objects of study and current scientific practices have a history and a reason for their existence because knowing them helps us understand and observe the changes in the face of new phenomena and global risks (Kawamoto et al., 2011).

Air Pollution in the Industrialized World

Pollution problems are not new. But they have changed over time. At the end of the 19th century, dense smoke floated over industrialized cities; thick columns of exhaust were symbols of economic power. Smoke seeped into popular culture and to a great degree formed a central element in representations of industrialization and urban life (Davis & Henderson, 2011). The idea of smoke’s harmlessness and its association with well-being can be observed in the widely used 19th century English adage “Where there’s muck, there’s brass” [i.e., money] (Mosley, 2006), as well as in the poem “The Smokeless Chimney” (Mosley, 2001).

In the United States, Germany, and Great Britain, complaints and campaigns against coal smoke emerged in parallel with these beliefs that smoke did not harm human health, to which Stradling, Uekoetter, and Thorsheim all attest (Stradling, 1999; Thorsheim, 2006; Uekoetter, 2009). “By 1907, in New York, Cincinnati, and dozens of other cities, middle-class women, physicians, businessmen, and engineers, acting through interest groups, had defined smoke as a problem” (Stradling, 1999). Smoke’s harmful character began to be observed. That said, these and other efforts on the part of organizations that were established in the most highly industrialized cities—the Manchester Association for the Prevention of Smoke, the National Smoke Abatement Institution, the Coal Smoke Abatement Society, among others—sought to curb the smoke produced by burning coal, often without great success because of industry stonewalling; producers saw no benefit to regulation.

The air-pollution problem took on higher visibility during episodes of deaths and respiratory diseases to which important and productive industrialized cities were subject, at a time when petroleum and natural gas were replacing coal. London’s Great Smog, which lasted from December 5 to December 8, 1952, had a singular impact on science, on public perceptions of air pollution, and on governmental regulations, due to its density and duration, its death toll in the hundreds, and to the measures to which it gave rise (Bell et al., 2004). Other analogous episodes occurred in highly industrialized cities such as Pittsburgh and Donora (Pennsylvania), Los Angeles, and New York (Davidson, 1979; Ross & Amter, 2002). These events led to rethinking the link between pollution and health, materialized the consequences of pollution, and made clear that air—an element indispensable to human life, without which humans cannot live for longer than 5 min—was polluted.

The term smog, a combination of the words smoke and fog, began to be used to designate a pollution type that—as historians Thorsheim and Stradling mention—became increasingly less tolerated and led to worries among greater numbers. Through research and measurements, international bodies such as the WHO and the Organization for European Economic Cooperation (OEEC) confirmed a new understanding of many chemical substances that were the by-products of the incomplete combustion of fossil fuels. Previously, smoke had been characterized by visual color-set and never properly studied in public-health-related terms. The idea of quantifying the main and most common substances that polluted the air (including suspended dust particles and sulfur dioxide), as well as establishing control mechanisms started to take hold in the United States and among European governments.

This opened up an incipient field of study that began to take on greater centrality and importance. A new corpus of experts emerged to define how to speak of the cause of these disasters with academic rigor, and, more specifically, to determine the “epistemic configurations” (Knorr, 1999). Specific practices and protocols were implemented to meet and understand the objects of study that the OEEC and WHO considered as the most dangerous for human health. ¹ In this sense, in 1969, the WHO published a guide that “recommended procedures for air sampling and analysis for identifying and estimating the most common pollutants” (WHO, 1969). This is how the study of air monitoring emerged with the characteristics we know today.

The term “air pollution” began to be used to designate changes to the “normal” composition and concentrations of the atmosphere. The focus of study, actions, and control was centered on “man-made pollution” or “human activity” as the main cause of loss to human health. Experience derived from workplace medicine was an important source of information when it came to identifying possible environmental pollutants and risks to the populace in general (Fressoz, 2002). Any compound that had been the cause of acute or chronic illness among industrial workers and miners could give rise to analogous effects in the general population. Extensive research in toxicology, pharmacology, and epidemiology provided a great deal of information on exposure to certain substances and their adverse effects on human health. ² In addition, many of the first measures designed to estimate air pollution made recourse to several methods commonly used in the industry to analyze air. Thus, in the first instance, the air inside factories became the model for free-flowing, outdoor air.

Although major industrial cities lived with the effects of smoke on human health, a host of local problems afflicted Mexico’s capital. These were linked to the altitude of the city at 2,200 m and its geographical location in the bed of a partially drained lake, surrounded by mountains: the Ajusco, the Iztaccíhuatl, and the Popocatépetl volcanoes to the south and east, the Monte de las Cruces to the West. Its topography and that of its surroundings distinguish Mexico City from any other city in the world. This means that the study of air pollution due to local conditions is quite complex.

Dust Storms From Drained Lake

At the dawn of the 19th century, German naturalist and geographer Alexander von Humboldt extolled the transparency of the air in the Valley of Mexico. A century later, in his Visión de Anáhuac, Mexican intellectual Alfonso Reyes (2002) picked up Humboldt’s earlier comments, to question them: “Is this where the air is clearest? So what did you make of my high metaphysical valley? Why does it cloud up, why does it turn yellow? Dusty whirlwinds blaze across it like fatuous fires.” Reyes was referring to the dust storms, which were linked to the more than 27,000 ha of land and dust that were discovered after the partial drying-up of Lake Texcoco. ³

Mexico City sits on top of the bed of a salty lake which was gradually drained in the course of various centuries, as Spanish colonizers sought to fashion a more comfortable and “salubrious” city, in the image of European cities that were built on the premise of a strict separation between water and land (Candiani, 2014). These salty waters were disregarded by the ruling elite and were polluted with spills and waste from the city.

Public works to drain the Valley of Mexico, begun in the 16th century, were finally completed by the early 20th century, under the government of Porfirio Díaz (O. L. González, 1902; Perló, 1999). In March 1900, the General Drainage of the Valley of Mexico was inaugurated. The idea was to build the modern city to which the governing elites aspired, by launching several urbanization projects, such as street lighting, a sewage system, and running water (Miranda, 2020), and improve the city’s hygiene.

However, draining the lake did not bring about the expected public health improvements. During the dry season, dust storms became more frequent due to two combined elements, one being large areas of land surfaced by dry and loose soil and the other, strong cold and warm winds converging to create immense dust storms. The Metropolitan Rating, a document produced by the Ministry of Public Health and Assistance pointed out that, over the course of 35 years, between 1923 and 1958, there were, annually, an average of 67.7 dust storms that lasted 1 to 3 hr and 28.5 that lasted more than 3 hr (Cacho, 1968; Figure 1).

Figure 1.

Map of the Federal Zone of Lake Texcoco, 1970. Produced by: Gabriel Gómez PUEC-UNAM.

Between 1912 and 1970, a series of projects geared toward dust-storm reduction were undertaken (Vitz, 2018), those that offered the following three solutions related to the use of the discovered lands. First, the works for “fertilization” basically consisted of washing the soil to eliminate the salts and allocating the land to agricultural exploitation. The second idea was reforestation and planting grass in the land that was discovered to have halophiles, salt-resistant plants. And, finally, the third proposal was the recovery of the lacustrine basin through the creation of small artificial lakes was another possible solution (Soto-Coloballes, 2019). These three ideas converged in the Lake Texcoco Plan, which put in practice these projects and considerably reduced the dust storms, finally managing to reduce them considerably (Cruickshank, 1998, p. 111).

An Atmosphere of Dust

Although it is difficult today to imagine dust clouds that ascended to great heights to darken the skies and whirled through the city at 50 km/hr (De Quevedo, 1927, p. 42), for decades, these were a serious and very particular local condition, which affected the lives of many citizens. In their wake, they left layers of dust that wore away the health of urban residents and at the overall aspect of the city. ⁴ From January to May, dust storms dirtied everything. This led to a popular refrain, “febrero loco y marzo otro poco” (“February is crazy and March still a bit more”; Figure 2).

Figure 2.

The photographs appeared on the front page of Mexico City newspaper La Prensa on 25 March 1947. The caption reads: “What a tolvanera! From one end to the other yesterday afternoon, Mexico City was on the receiving end of several tons of saltpeter-laden dirt from the former Lake Texcoco. From six to seven pm . . . this horrible, homegrown ‘simún’ had citizens out of their heads. In addition to the unamusing joke for women—who struggled to keep skirts in place—the dust-filled gusts made quick work of throats and temporarilyblinded anyone without the right pair of glasses. We’ll see the fall-out today: scratchy voices and irritated eyes.”—“Febrero loco, marzo . . .”

Dust storms are characterized by their brownish hue which made them easy to track against a clear sky, and by the fact they could be “immediately felt on exposed skin (and other) surfaces, turning the air almost unbearable” (Jáuregui, 1989). Their effects were immediate; their presence evident and tangible when compared with common smog. The relatively large dust particles from the “dust storms” could, because of their size, be appreciated at simple sight and also settled easily, and though they were, indeed, a cause for dirtiness in the city, discomforting and harmful for individuals, it was thought that they could not access the human respiratory system.

During a large part of the 20th century, Mexico City was affected by dust storms that contaminated foods, leaving bloodshot eyes, conjunctivitis, coughs, sneezing, colds, and other respiratory ailments in their wake. Studies such as those of physicians Antonio Prado Vértiz (1910–1973) and Pablo Murillo Pulido confirmed the frequency of illnesses caused by dust storms. In 1957, the Gaceta Médica Nacional published its clinical review of 210 cases of infectious laryngeal-tracheal bronchitis treated at the Hospital Infantil de México, between 1943 and 1956, concluding, “the greatest contingent of patients came from the east side of the city, whose neighborhoods lay at the lowest altitudes, were subject to strong winds and lacked forests or geological protections; they were the front door to dust storms” (Prado & Murillo, 1957). Due to uneven urban development, there were socially and politically disfavored areas that suffered the consequences of the dust storms most acutely; the poorest who lived in areas at the edges of the city that had been lakebed was the most adversely affected.

Dust storms were also thought to be responsible for certain gastrointestinal illnesses. They were vehicles for fecal matter since for years, the city’s raw sewage was channeled through the San Lázaro Canal to Lake Texcoco (Cházaro, 2007). So, during the dry season, the dust storms transported these soiled sediments, which contributed to an increase in diarrheal diseases, because they bore pathogenic and nonpathogenic microorganisms, protozoans and parasites, as was later confirmed (Valenzuela & Calderón, 1973).

Other accounts pointed out that dust storms affected farming and ranching:

When the wind blows and moves across land that lacks any protective cover, that is, trees or grass, it kicks up dust storms and sweeps away metric tons of good, fertile earth, that it will deposit somewhere else it is not needed, or, even worse, covering crops or grasslands, which leads to real harm. (Beltrán, 1945)

The densest ones even paralyzed traffic and prevented planes from landing at Mexico City airport.

Studies on Dust Storms

This section explores how dust storms were introduced into scientific discourse. The catastrophes experienced by highly industrialized cities forged a variety of ways of conceiving of pollution, some of which preceded while others were simultaneous with what the WHO conceived as man-made air pollution. In other words, current concepts have a history and a memory, as Ian Hacking (2004) has suggested, they are the product of changes and processes that need to be explained.

In 1923, the Tacubaya Meteorological Observatory began to systematically record the frequency, duration, and intensity of dust storms, and in 1940 the visibility, that is, the transparency of the atmosphere. Although the origin of this pollution was fully identified, its contents were unknown. They believed that dust storms carried biological material, which was thought to be responsible for making the population sick.

The Institute for Public Health and Tropical Diseases took a keen interest in the biological content of dust, in response to the high frequency of respiratory and gastrointestinal ailments among city dwellers; these ailments were thought to be related to microbes and germs. The two studies I present below constituted an effort to learn about the microorganisms present in Mexico City’s atmosphere.

In 1943, the Department of Mycology published “Airborne Fungi in Mexico City and Their Relation to Atmospheric Factors.” The authors, physicians Antonio González and Catalina Orozco, thought that a seasonal and by-hour mycological investigation would be useful for the allergy clinic and would produce knowledge about typical pollutants; as they affirmed,

we consider it to be of some importance to know the mycological population of the air during different months of the year and at different hours of the day and the relation these might have with atmospheric factors. This study was similar to the 25 explorations that had been carried out, up to 1942, in other cities. (Gónzalez & Orozco, 1943)

A season and hourly survey was made of the air-borne fungus in the city of Mexico using the plate method, studying its relation to atmospheric factors. The records were taken from march 1942 to march 1943. Nineteen different Genera were found. Slight seasonal fluctuation was observed in the total number of colonies increasing during April to June, but not in the different Genera, nor did they observed hourly distribution neither in the total number of colonies or for the various Genera. An apparent correlation was found in the total number of colonies and the velocity of the wind and inversal with tension and relative humidity. (Gónzalez & Orozco, 1943)

The physicians were able to prove that dust storms made people sick.

For their part, in 1957, Gerardo Varela and Marta Percastegui from the laboratory of bacteriology of the Institute for Public Health and Tropical Diseases published “Bacteriological study of Air in Mexico City,” where they sought to learn which microorganisms were habitually present before and during dust storms, and which could be found in different areas, such as industrial zones and business districts, places of public entertainment, school zones, hospitals, and churches. They exposed petri dishes (10 cm in diameter with simple agar, blood agar, endo agar, and Sabouraud agar) in the air for 1 min; these samples were incubated, isolated, and studied to identify the developed colonies (Varela & Percastegui, 1957). The results of the study demonstrated that, in effect, dust storms did indeed mobilize pathogens in significant quantities toward congested zones in the city, causing epidemic dispersion. This led the authors to conclude that “collected data show the significance of air pollution in Mexico City” (Varela & Percastegui, 1957), given the identification of 59 bacterial species.

What these above studies understood as air pollution in Mexico City was much more closely linked to the presence of microorganisms in the air than with particles or gases emitted by industry or automobiles. The presence of microorganisms in the environment was linked to poverty, lack of cleanliness, and ignorance—in a word, to a lack of “development”—whereas the presence of smog was related to the production of goods and services and with automobile use, that is, with rich, modern societies. The distinction was formalized in 1958 by the panel of experts at the WHO—which assessed and organized programs to fight and prevent air pollution in member states—when it

decided to limit itself to man-made air pollution only [contaminación artificial] ⁵ and to exclude from consideration the pollutants of natural origins, such as pollen, products of volcanic-activity or the decay of rocks and organic matter, and dusts from outside the earth’s atmosphere. (WHO, 1958)

The vast majority of the literature from that time explained environmental problems as an outcome of industrial development and unbridled population growth (Commoner, 1971, 1976; Enrlich, 1968).

Emerging Studies on Air Pollution

Mexico’s Ministry of Public Health and Assistance, which paid particular attention to the WHO actions, took up an air pollution study. Carrying out this study was essential if Mexico sought to be a member of the group of “developed”. The study recognized the importance of dust storms and industrial emissions in the city’s northern districts nations; after all, filth was seen as contrary to civilization and progress (Borowy, 2013). Between 1958 and 1966, the ministry operated four stations for dust collection and analysis, from the physical-chemical point of view. In 1960, it published its “Preliminary Report on Air Pollution in Mexico City,” in the journal Boletín de la Higiene Industrial. The study recognized the importance of dust storms and of industrial emissions in the city’s northern districts, in addition to those derived from unprecedented growth of population, services, and vehicle use (Viniegra & Bravo, 1960).

This study was continued by the Chemistry Division at the Institute for Applied Science the National University of Mexico. In June 1960, Ingeniería Química published an article titled “Study of Gravity-Induced Dust Deposit in Mexico City” by Humberto Bravo, Armando Báez, and S. Lares. The study measured air pollution using a method based on gathering and estimating the amount of dust deposited by gravity during (for 12 months). For gathering the samples, glass jars with a 2.5-L capacity and a height of 20 cm were used; they were placed in the roofs of 28 buildings, with an average height of 12 m, for 30 days. After exposure, the glass jars were sealed and taken to the lab for analysis. A second step involved drying and weighing the dust collected in the vials jars and expressing outcomes in tons/square kilometer/30 days) (Bravo et al., 1960). This study agreed that the air pollution problem was two-sided, a function of the dust storms and disorderly, rapid, and chaotic industrial and demographic growth.

A similar study, “Biological Considerations Regarding the Nature of Dust Collected in the Valley of Mexico Basin’s Lake Regions,” was published in the Revista de la Sociedad Mexicana de Historia Natural. Biologist Ángel Silva placed eight stations to pick up the dust, using what he called a “dust-catching device,” a grooved, hexagonal shell that let air flow freely and deposit dust on two glass slides, coated with a thin layer of glycerin. Samples were delivered weekly to laboratories, to be counted using a petrographic microscope and a micrometric grid (Silva, 1960). The results obtained from the quantification of dust allowed the researchers to note that “a 4,000-square-kilometer surface in it the Valley of Mexico basin is affected by dust storms that originate at Lake Texcoco,” as well as due to industrial emissions (Silva, 1960).

To collect the dust, the Ministry of Public Health and Assistance, Bravo and Silva used the simplest possible tools: glass vessels and plates coated in petroleum jelly or glycerin. All that was needed to collect samples was that the dust falls into the glass jars or adhere to the glycerin-coated plates for later laboratory analysis. Glass vessels could be acquired with relative ease, because they were readily available on the market and because they were cheap. As for Silva’s dust-catching device, designed by the researchers themselves, it required neither large-scale investment nor special facilities, not even electricity. Because of their limited application and lack of specificity, the OEEC did not consider these devices fully scientific, even if some programs for monitoring used them to observe the “most notorious” problems of air pollution problems (Council of Europe, 1964).

To quantify the dust they collected, the Ministry of Public Health and Assistance and Bravo used gravimetric analyses, whereas Silva used a microscope and a millimetric grid. Nevertheless, what links together these investigations, including those undertaken by the Institute for Public Health and Tropical Diseases, is the affirmation of the existence of air pollution in Mexico City. Yet it was obvious that there was a difference in what they each identified as pollution and in the ways they addressed socio-territorial attitudes and dynamics. The notion of pollution that permeates the studies carried out by the Institute of Public Health and Tropical Diseases correlated airborne bacterial increases with dust storms. Viniegra and Bravo’s studies, on the other hand, produced statistics that demonstrated the existence of air pollution beyond simple perception. Their estimates, more than an analysis of content, record observations and comparisons between the dirtiest months and the most affected zones. Biological material was excluded from these quantifications. Bravo and his team collected dust in glass jars using a mercury-dichloride solution. This highly toxic compound prevented the biological matter from turning up in the sample. Finally, Silva did separate biological material; on the contrary, he indicated the percentage of biological material in the sample but stopped short of growing pathogens as had been the case with González, Orozco, de Varela, and Percastegui. Silva’s work was circumscribed to the Texcoco area, thought to be the source of pollution for an enormous surface area; his weekly samples made it easier to detect possible correlations in component variations.

These different studies were grounded in similar material technologies, which tied measurements and samplings powerfully to the places where they were collected. Years later, air pollution was shown to affect all sectors of the population, the rich as well as the poor; it became a unifying condition, which affected everyone. Air pollution was no longer attached to particularities of the urban grid; the city’s atmosphere became homogeneous.

Natural Pollution Versus Chemical Substances

As industrial emissions increased and the population grew, the State commissioned a study to measure air pollution following international standards. In 1967, the Ministry of Public Health and Assistance joined the Pan-American Network for Standardized Sampling of Air Pollution, administered by the WHO. The studies on dust called for the use of specific instruments, partially in response to the demands for the standardization of legal measures against pollution.

The purpose of the agreement was to carry out their program called Red Panamericana, which consisted in quantifying suspended dust particles and sulfur dioxide, among other pollutants, to remedy the shortage of technical information and to study the situation comparatively to other Latin American cities that also participated in the program, for which 14 monitoring stations were installed in Mexico City, according to the instructions, measurement methods, and procedures indicated in the Procedures Manual (WHO, 1970).

The instrument for sampling the suspended particles and sulfur dioxide consisted of an electric vacuum pump that sucked the air from the environment. The air entered through a plastic funnel and a hose through which the absorbed air passed, it then penetrated a paper filter, where the suspended particles were to stay; finally, the absorbed air reached the washing bottle or bubbler, which contained a diluted solution of hydrogen peroxide with pH (hydrogen potential) of 4.5 for the absorption of sulfur dioxide. And to know the volume of air sampled during the 24 hr, a rotameter was used—an instrument for determining the flow of liquids or gases in pipes. This device was covered by a protective shell, to protect it from the weather. Once the sample was taken, it was brought to the laboratory for analysis, which consisted of estimating the darkness of the stain with the Smoke Stain Reflectometer, from the Evans Electroselenium Limited manufacturer. With that result and a series of other formulas, the concentration of the sample collected per square centimeter was estimated. These results were sent each month to the Pan-American Network offices in Lima, Peru.

This organism assumed the tasks of evaluation, prevention, and control of air pollution based on concepts, protocols, and norms which the WHO itself considered appropriate or important. It was a way to shape policy and to forge political rhetoric that necessarily overlooked local forms of knowledge as it put together a vision of technological determinism. From that perspective, the dust itself was not as important as the suspended dust spewed by industrial smokestacks and automotive tailpipes. These last invisible to the human eye.

In light of new chemical hazards, the study of dust storms decreased in relevance because it was assumed that the storms did not gravely upset human health in comparison with new dangers, that had led to hundreds of deaths in highly industrialized cities. That said, dust storms did affect the population in general and particularly the poorest residents, almost always located at the city’s peripheries, close to the lake’s discovered bed.

The study of “naturally-caused pollution,” such as the dust storms, was decreased as part of a consideration that lack of toxicity did not undermine health, which was later made official in Mexico’s Federal Air-Pollution Prevention and Control Act, published in the nation’s official federal gazette on March 23, 1971. This act classified sources of pollution into artificial and natural; this latter category would later be broadened to include “eroded and drained lands.” That said, dust storms were not simply a “natural” problem; since colonial days and particularly in the 19th century, as noted, several projects struggled to drain Lake Texcoco, with the effect of producing dust storms. So, after all, dust storms were man-made, even if they were classified as “natural.”

As a result of their classification, dust storms were no longer being studies by the organisms in charge of managing air quality. Ministry of Public Health and Assistance was interested in smaller particles (suspended dust particles, later known as suspended particulate matter [SPM]) in very thin dust, toxic, and not perceptible by the human eye which could be seriously harmful (Speizer, 1969). Whereas the particulate matter from dust storms were relatively large, too large to enter the human organism and sicken and cause him death.

Second, because of the settlement and consequent construction of housing on what was once lakebed. The counties surrounding the lake increased their population so much that in 1980 Nezahualcóyotl had 1,000,341 inhabitants, La Paz 99,436, Chimalhuacán 61,816, Chicoloapan 27,354, Ixtapaluca 77,862, and y Ecatepec 784,507 inhabitants (Lezama et al., 2002).

And another factor was that the frequency and intensity of dust storms diminished as the Plan Lake Texcoco was put into place, starting in the 1970s, which had the objective of “reducing environmental pollution caused by dust storms” (Lake Texcoco Commission, 1983). A decade later, the managers of this program presented their unique successes:

for the first time in the year of 1983, there were no dust storms, which traditionally fell on the city; because grass had been planted, thus transforming the desolate landscape, more than 6 thousand hectares, in which cattle and sheep thrived. (Lake Texcoco Commission, 1983)

In addition, in the 1990s the construction of several artificial lakes and lagoons (Xalapango Lagoon, Nabor Carrillo Lake, Recreational Lake, Churubusco Lake, and Time Regulation Lake) was completed in the same area (Cruickshank, 1998).

However, since 2000, the vegetation cover and reforestation program has been intentionally neglected, due to the project for building a central airport in that area. The lands will be uncovered, so the extensions of particles by wind erosion have once again become a problem (Díaz-Nigenda et al., 2010). This also happens in other parts of the world, where dust storms have intensified, for example, since 2004 the cities of southern and western Iran are affected by dust storms, causing various health issues and economic damage (Geravandi et al., 2017; Goudarzi et al., 2017; Khaniabadi et al., 2017).

Conclusions

This essay has argued that the notion of pollution is flexible and historically contingent, constantly redefined and reinvented, capable of new meanings and uses when situated in specific scenarios. Until very recently, dust storms were what polluted and obscured Mexico City’s air; the dangers of smog derived from industrialization and economic growth barely affected the residents of Mexico City. However, in the short space of just a few decades, especially in the course of the 1970s, dust storms moved to a secondary plane while the “new dangers” of the Western world came to the forefront. New hazards displaced old ones in a reclassification which identified pollution as the presence of certain substances in the air derived from the incomplete combustion of fuels. The model shifted from medical/bacteriological definition of pollution to one that rooted in chemistry and engineering.

Both international and domestic factors played a crucial role in this process of transformation. The local definition of risk, associated with specific notions of health and with a precise definition of quality of life, practically disappeared when a new notion of pollution took hold. An unbreathable atmosphere, the result of dust storms that occurred during the dry season and caused sneezing, coughing, pink eye, and other ailments, had been identified as the pollution proper to a city whose lake had drained. In this scenario, the notion of pollution centered on dusts perceptible to the naked eye, coming precisely from the large areas of saline, dry and loose land where the great Lake of Texcoco once was. By the 1970s, this notion changed, largely in response to new configurations adopted by international organizations and industrialized nations. Eventually, Mexico also adopted this new notion of pollution. Smokestacks and automotive tailpipes became the visible culprits of the problem.

Dust storms, the result of public efforts to drain the Texcoco Lake, came to be considered natural pollution and were displaced from the center of both lay conversation and scientific study, for being supposedly nontoxic. From that point on, it was artificial pollution—the kind thought to poison and pollute the air—and chemical substances such as particulate matter, and sulfur dioxide the product of economic and technological development, that were shown to affect the health of all city dwellers, regardless of where they resided. Hazards came to be limited to specific, unseen dangers. The city’s atmosphere became a homogeneous space. Under this new perspective, not only what is understood by pollution, but also the objects of inquiry have changed, at the same time that new practices such as air monitoring emerged.