Emissions from factories and cars, smoke from heaters, airborne dust and pollen … all contribute to thinning the air in cities. This type of pollution can cause different health problems, especially respiratory and cardiovascular . To find out how stale it is, different gases are analyzed. The most important in this regard are ammonia, formic acid, methanol and ozone. Now, a team of researchers led by Karen Cady-Pereira, an Earth Science expert at Atmospheric and Environmental Research in Massachusetts, has used data from NASA’s Aura satellite to examine the air of 18 megacities. , that is, urban areas with more than 10 million inhabitants.
According to a report in the journal Science , the probe, which has been studying the Earth’s atmosphere for almost 13 years, flies over each of these metropolises every 16 days or so at the same time. Thus, Cady-Pereira and her collaborators have been able to determine that the worst concentrations of ozone occur in Karachi, in Pakistan . Of the 300 measurements made over a year, almost a third exceeded the limits considered dangerous, which can give rise to a kind of polluting haze known as smog.
In the case of ammonia, a compound that is used in fertilizers and that contributes to the formation of particles that are particularly harmful to the lungs, the mega-city most affected is Delhi, India , where the red lines were exceeded by 73.5% of the times. It is followed by Dhaka, in Bangladesh (51.6%) and Calcutta, also in India (47.1%). However, in other parts of the world, such as Buenos Aires, there are also unusual peaks, perhaps as a consequence of intense livestock activity .
The scientists, who hope to publish their results in the journal Atmospheric Chemistry and Physics , have also observed that the burning of waste and biomass and the use of fire to clear areas and make them suitable for planting crops causes a notable increase in harmful compounds in Lagos (Nigeria) and in Mexico City . In this same megacity, air quality drops sharply between March and June.
Cady-Pereira and his colleagues explain that in this phenomenon, other factors must also be taken into account, such as the position of the city with respect to the equator or the winds, for example.
Image: Wili Hybrid via Wikimedia / GNU / CC
