Particulate Matter In Air At Unsafe Levels In Majority Of Large Cities, Study Finds

Most big cities around the world are above World Health Organization-recommended safe levels of particular matter in the air, with 42 percent at dangerously high levels, and only 8 percent within safe limits, a new study finds. At just 2.5 microns in size or smaller, fine particulate matter (PM2.5) is “a leading environmental health risk” and the cause of fatal cardiovascular and respiratory diseases, as well as cancers.

The cities within safe limits are exclusively within wealthy countries, while those at dangerously high levels are located primarily in more recently industrialised Asian countries, where there are less emission controls to reduce particulate matter and less stringent environmental regulations, and where many wealthy countries have relocated polluting industries.

Utilising estimates of PM2.5 mortality rates in the 250 most populated cities in the world today, the study released by Nature on Friday concluded that city-level information will be critical in determining actions to improve air quality, reduce CO2 emissions, and design sustainable energy sources for the coming decades. According to the study, while regional and countrywide information on the health hazards of PM2.5 is plenty, there has been a severe lack of data at the city-level.

People wearing respiratory masks during smog in Beijing, China. Photo: Reuters

Among the cities examined, the study found that only 8 percent returned PM2.5 levels below what the World Health Organization has defined as an acceptable annual average. These cities were exclusive to wealthy, economically developed nations, including Sweden, the United States, Canada, Australia, and Brazil. In contrast, the study revealed that 42 percent of the examined cities returned dangerously high PM2.5 levels, with the remaining cities falling at or close to the WHO guideline.

Further findings challenged correlations between economic development and levels of PM2.5. While cities in Asia were present in both the top ten cities for population-weighted PM2.5 and the top ten cities for PM2.5 mortality rates, the former category was shared with cities in Africa while the latter was shared with those in Europe. This suggests that while African cities are experiencing an increase in PM2.5 levels during a period of industrial expansion, post-industrial European cities are reporting greater numbers of PM2.5 related illnesses and fatalities.

Unlike CO2 emissions, PM2.5 includes naturally occurring pollutants which can further worsen air quality in tandem with human-made sources stemming from different industrial sectors. For example, the Egyptian capital Cairo is geographically vulnerable to poor air quality because of its location within a valley where sand and dust blown in by western winds are trapped and combined with industrial pollution under the North African sun.

The map from the study below details the distribution of deaths linked to particulate matter across cities worldwide:

Source: Nature (2019)

Carbon Dioxide Independent from Fine Particulate Matter; Opportunities to Reduce Both

A result of production and manufacturing, CO2 emissions are another challenge in the mission to improve air quality worldwide. However, while capable of combining with fine particulate matter to create hazardous conditions in cities, the study reported that there was “no association between PM2.5 and CO2 emission rates.” Instead, increases or decreases of one rate may be independent of the other, a concept found to be true particularly among cities in wealthier regions.

Identifying three key factors, the study explained the independence of CO2 emission rates from PM2.5 levels in wealthier regions:

First is the ability of wealthy regions to develop and implement technology, such as “end-of-pipe emission controls,” which reduces PM2.5 levels at a greater rate than CO2 emissions. Second, the study focused only on the 250 largest cities in the world. This presents the possibility that production facilities may have been relocated to smaller cities or distant regions, causing air pollution levels within city limits to decrease while CO2 emissions remain minimally changed as a result of large populations. Relocation on a global scale is recognised as the third factor as wealthier nations, such as the United States, outsource large production facilities to cities in other regions of the world, thereby “simply (moving) pollution from one place to another.”

Declaring that “the challenge of urban PM2.5 can also be viewed as an opportunity,” the study suggests that government policy, along with continued innovations in green technology and sustainable energy sources, could reduce CO2 emission rates in cities already successful in PM2.5 efforts, and help manage air pollution in actively industrialising cities.

This call to action comes six weeks ahead of the United Nations Climate Summit on 23 September in New York, where discussions are expected to address climate-related health hazards and policies for climate change mitigation.

Image Credits: Reuters, Nature.

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