Pollution hits poor people and people of colour hardest. This is not an entirely new assertion, and it encapsulates the problem of environmental injustice, first theorised by a number of researchers between the 1960s and 1980s. The studies of that era had confined themselves to analysing air quality in a number of large cities, finding a difference between wealthy neighbourhoods, inhabited mostly by white people, and poor neighbourhoods, inhabited by black people.

All of this has been confirmed by a new American study published in Plos One, which also demonstrates that this theory holds true across the entire United States, including historically less polluted cities and rural areas.

When nitrogen dioxide hits black communities

The poor and minorities are reportedly 38 per cent more exposed than white people to nitrogen dioxide, a highly toxic gas that causes cardiac and respiratory problems. According to Julian Marshall, professor of environmental engineering at the University of Minnesota, "the level of disparity is high, with likely consequences for health."

Nitrogen dioxide is said to be responsible for seven thousand premature deaths each year among African Americans, primarily due to cardiac problems. The worst city in this respect is New York and the metropolitan area extending as far as Newark. New York's neighbourhoods have recorded a high disparity in the air quality data collected. Then come Philadelphia, the Bridgeport–Stamford metropolitan area, and Boston.

The poor cannot escape pollution

The most polluted areas are those through which motorways pass, where landfill sites are located, and where there is a strong concentration of industrial plants. By contrast, trees — found mostly in the "cleaner" neighbourhoods — are a sign of the absence of heavy traffic and concrete. The conclusion Marshall reached is that economic factors have been decisive in creating artificial ghettos: only the poorest remain, because they are forced to, in their homes even after a motorway or a polluting plant has been built nearby. Breathing, as a result, the consequences.