A study published on Wednesday states that the air can be transformed into new substances more toxic and persistent than the original pollution.
The study published in Nature found that these products are present in the atmospheres of 18 big cities, including Lagos, New York, Tokyo, and Warsaw.
The danger of different chemical pollutants is assessed by how long they remain in the environment, how toxic they are, and how much they affect living things.
The approach has been limited to a list of known substances and does not take into account how they may change as they break down.
A new framework is proposed by the research that uses laboratory tests and computer simulation to predict what chemicals will be in the air and how toxic they will be.
John Liggio, a research scientist for Environment Canada, was the main author of the study.
Liggio told Agence France-Presse that they are chemicals added to a large variety of materials to delay the start of fire.
In a laboratory, they observed how the chemicals changed over time when in contact with oxidants in the air and found that they gave rise to 186 different substances.
They found 19 of the new substances from the five most common flame retardants. The 19 had never been identified in the atmosphere before.
The team used computer simulations to gauge the persistence, toxicity, and bio-accumulation of the derived chemicals.
They discovered that the new chemicals could be more toxic than their parent chemicals, and that some of them could be 10 times as toxic.
The framework should provide a new avenue for including transformation products in routine air-monitoring programs and for prioritized transformation products of high concern for further scrutiny, according to the study.
The study looked at nine common chemical pollutants and their 19 daughter chemicals in the urban air samples, but Liggio says these results are only the beginning.
He said that there are thousands of different chemicals, and that future tests will look at vehicle tire chemicals.
The goal is to test the toxicity of pollutants in real-life studies, going beyond the computer modelling used for this study.
Agence France-Presse.
