The air quality of Mexico City has improved since it was, in 1992, the most polluted megacity in world. This is down to government initiatives such as the ProAire programme. Improvements are still required, though, and the city’s infrastructure needs to be environmentally sustainable. A case in point is the extension to the city’s Manuel Gea González Hospital, which was designed to neutralise pollutants and improve air quality, which is particularly important in an area with so many hospital patients.
In 1992, Mexico City was singled out as the most polluted megacity in the world. It came just ahead of São Paulo in a World Health Organization (WHO) and UN Environment Programme (UNEP) study of ‘Air Quality in 20 Megacities’.  Pollution levels used to be so high and, allegedly, “its skies so poisonous that birds dropped dead in flight” as they flew over. 
The city’s “levels of sulphur dioxide, suspended particulate matter, carbon monoxide, ozone, lead, and nitrogen dioxide all exceeded the [WHO’s] health protection guidelines.  At the time, researchers hypothesized that the pollution was causing about 35,000 hospitalizations and 1,000 deaths every year.”
In 1995, the Mexican government launched the ProAire programme to combat the increasing levels of pollution. “In 1992, there were only nine days in which the air quality [in Mexico City] was excellent.  Thanks to several measures, 2012 registered 248 days of good air quality.” There was more to do, though, and there are several initiatives to make this happen, not least in the design of new and existing architecture.
Within the context of the ProAire initiative, a hospital building in Mexico City, the Torre de Especialidades, was extended and redesigned to transform air pollutants into harmless chemicals. “The original Manuel Gea González Hospital was designed by the architect Manuel Villagrán and was completed in 1942.  After many years of service, in 2013 a new medical specialities tower [the Torre de Especialidades] was built, for whose construction environmental needs were taken into account.”
Elegant Embellishments of Berlin installed a 2,500 square metre depolluting façade made of proSolve370e on the tower. “These modules are coated with a special pigment that, when hit by ambient ultraviolet light, reacts with urban air pollutants, breaking them down into less noxious compounds like carbon dioxide and water. The pigment itself remains unchanged, which means the modules can keep purifying the air for as long as a decade." 
What did and didn't work
Stakeholder Engagement Good
The main stakeholders were the Mexican government, in particular the Ministry of Health, the administration of Mexico City, the management and medical staff of Manuel Gea González Hospital, and Elegant Embellishments who were responsible for implementing the façade.
Political Commitment Strong
There is strong national commitment behind the ProAire programme and the need to continue the improvement in Mexico City’s air quality since the programme’s conclusion. The Manuel Gea González Hospital project, which is funded by Mexico’s Ministry of Health, is “part of a US$20 billion investment in Mexico’s health infrastructure.” 
Public Confidence Weak
There is no evidence about the public’s view of the sustainable hospital extension. However, there is evidence about citizens’ views of anti-pollution efforts in Mexico City.
The Mexico City Government set out to find out what the public thought about its air quality initiatives “with support from Canada’s International Development Research Centre … and the Netherlands Trust Fund, through the World Bank and the Pan American Health Organisation.” 
The researchers then took to the streets. “Questionnaires administered by the research team to close to 4,000 residents in all sectors or delegations of the city showed, close to 30% believe the government’s motives in seeking to reduce air pollution to be self-serving. More than 30% also think that the government’s online air quality reports are false … Close to 40% could not identify any of the government programs to improve air quality. The remainder considered them necessary evils — restrictions rather than preventive measures.” 
Clear Objectives Good
The broad objective of the initiative was to contribute to Mexico City’s anti-pollution measures that are improving air quality in the city. The Manuel Gea González Hospital façade was developed to reduce air pollution from mono-nitrogen oxides (NOx), volatile organic compounds (VOCs) and sulphur dioxide in the immediate area.
The façade of the hospital tower uses a new type of tile called proSolve370e. “According to its inventors, the Berlin-based design firm Elegant Embellishments, [the tile] can neutralise the chemicals produced by 8,750 cars every day."  This is because “the undulating shapes of the facades maximise the surface area of active coating to diffuse light, air turbulence and pollution”. The actual number within the vicinity of the hospital was 1,000.
The tiles for the hospital tower were rigorously prototyped and tested. “Prototypes for Torre de Especialidades were installed at Elegant Embellishments’ thermoforming factory in Ulm in April 2012.  A 1:1 scale patch was installed onto steel verticals to test the assembly and estimate installation times. The patch was composed of 4 Mega Panels (clusters of 3-6 modules) taken from the top left corner of the facade in Mexico.”
It is a government initiative which is fully funded by Ministry of Health as part of its three-year US$20 billion investment in the country’s health infrastructure. From the technical point of view, it should be able to function successfully for a decade.
As compared to other conventional methods of controlling pollution, it is feasible to adopt this initiative, since it can neutralise emissions from 1,000 vehicles in the vicinity of the hospital. “Due to their lightness, the modules don’t require heavy machinery for their installation. The pieces are mounted on huge panels on the ground which are later mounted to a vertical grid on the façade." 
Empresas ICA SAB, the troubled Mexican construction company, was the main contractor for the hospital tower, and Buro Happold New York was the structural engineer. The design of the façade was “made by a German team of designers from Elegant Embellishments and combines the polluting particles capture function with aesthetics. 90% of the façade (about 2,500 m2) is covered by a vertical metal structure that holds about 500 blocks assembled like a puzzle." 
The success of the façade can be monitored by checking air quality levels in its vicinity at regular intervals. Since it cleans the air inside the building as well, checking the change inside the air quality is also a valid indicator. The relevant pollutants are NOx, VOCs and sulphur dioxide.
The main administrative actors, like the city administration, the Mexican Ministry of Health and the Manuel Gea González Hospital, shared an alignment of interest with the design and construction team to execute their objectives.
The contractors collaborated closely with each other. For example, the Elegant Embellishments team worked closely with the structural engineers. “With help from the New York office of Buro Happold, the two devised Mega Panels, a clustering system for the tiles to connect using CNC-milled plastic plates.  For the 509 Mega Panels used on the hospital façade, Elegant Embellishments generated 500 distinct drawings. Each represents a unique configuration of tiles along with connection points and front and back elevations. They then had to train skilled workers to install them.”
The project was also strongly aligned with the air quality objectives of the national and city administrations.