Changes in the amount of air pollution over the world's largest urban agglomerations have pointed to their root causes - forest fires, debris, poor energy and poor location.
New data on air pollution in the world's largest urban agglomerations - megacities and "megacities" with a population of tens of millions of people are presented. The centers of Pakistan and India became the leaders of the anti-rating, and scientists assessed the role of various factors in seasonal changes in the level of pollution. The results of the work are being prepared for publication in the journal Atmospheric Chemistry and Physics.
The study was conducted by a large team of US scientists led by Jennifer Hegarty. Their work was based on observations made by the tropospheric emission spectrometer (TES), which operates on board the American meteorological satellite Aura. The orbit of the probe is designed in such a way that it can conduct observations of every point on the Earth every 16 days, at approximately the same local time. This made it possible to track changes in the content of ammonia, methanol, formic acid, ozone and other gases in order to understand how the features of the relief and climate affect the state of air in "megacities".
G. Grullón / Science
With ozone, the situation is worst in Pakistani Karachi (population about 24.3 million people): for about a third of days, the amount of this active gas in the lower atmosphere was above a safe level. Records for the content of toxic ammonia were set by the Indian Calcutta (14.8 million people), where its content remained above the norm 47.1%, 3 million) from 51.5% of days.
G. Grullón / Science
The key factor that leads to changes in the content of pollutants, scientists say, is the seasonal burning of biomass - forest fires, burning of plant residues in fields and just garbage. In particular, over Mexico City, levels of the same toxic gases rise sharply from March to June - the time when nearby farmers are treating fields with fire, starting new sowing.
However, many of the largest urban agglomerations suffer without the help of fires. Nigerian Lagos (21 million people) is even more polluted by Mexico City, the main culprits of which are an outdated electricity system and difficulties with garbage collection and disposal. As a result, the local population actively uses diesel generators, which sharply deteriorate air quality.
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The authors also mention the influence of geographical factors. In particular, the same Mexico City is surrounded on three sides by a mountain range, which delays the influx of pollution from distant fires. Lagos is close to the equator, and strong solar radiation contributes to the formation of ozone, and the wind from the ocean keeps pollution over the city.
Sergey Vasiliev
