Why Has Pollution Not Fallen in Some Cities?

The lockdown measures imposed by governments across the world in order to slow or stop the spread of COVID-19 may well precipitate the next economic recession – but they aren’t completely without their upsides, either. The worldwide network of urban air quality monitors, alongside data collected by satellite images from space, show that air pollution has dropped off significantly since quarantine measures were first introduced.

The phenomenon was first noticed in China, especially over Wuhan City and the surrounding area, but has since spread across to Europe and other parts of the globe. However, not everyone has seen concurrent levels of air quality improvement; many parts of the USA, for example, are experiencing similar levels of pollution as before, while some cities have even witnessed an increase. Why?

A variety of variables

Encouraging falls in concentrations of nitrogen dioxide (NO2), particulate matter (PM), sulphur dioxide (SO2) and formaldehyde (CH20) have been witnessed across China, France, Spain, Germany, the UK and the Netherlands, all of whom have had some form of lockdown controls in place for at least a month. All of those substances are toxic, damaging or even carcinogenic to humans as well, spelling good news for the residents of the urban epicentres in question.

However, a comprehensive analysis of the data provided by satellites is yet to be conducted, while there is room for doubt that the slump in pollution has been wholly caused by coronavirus-related activities (or lack thereof). For example, NO2 is wont to fall by around 50% in the northern hemisphere between January and May due to the angle at which the sun’s rays come into contact with the Earth. Nonetheless, the fact that current concentrations of the pollutants are markedly better than this time last year is a positive sign.

The US underperforming

By contrast, the USA has not witnessed anything like the same improvement in its air quality performance compared to its Asian and European counterparts. According to the European Space Agency’s TROPOMI instrument, Los Angeles is the only American city that has seen a significant drop-off in its pollution and that anomaly could be explained away by the fact that the coastal city has enjoyed an unusually high amount of rainfall in recent weeks.

Elsewhere, New York has shown a slight improvement in its concentrations of PM, but some parts of the country have even deteriorated in terms of air quality. Unsustainable farming practices in Mexico, such as stubble burning to make way for the next season’s crops, have led to higher concentrations of pollution in much of the central USA. What’s worse, many spectators are fearing that President Trump’s outspoken mistrust of environmental issues and support for damaging industries (such as coal-fired power stations, despite their well-publicised complications) may mean that any short-term benefits are immediately rolled back when the economy is reopened in any case.