Delhi, Kolkata Top List of World’s Most Polluted Cities; India Mourns Rising Levels of PM 2.5 and Ozone Air Pollution

The report, titled Air Quality and Health in Cities, is a part of an ongoing global effort to study the devastating effects of air pollution on human ecosystems all around the world, encompassing data from over 7,000 cities in 116 countries.

As per the report, exposure to PM 2.5 air pollution — one of the most consistent predictors of cardiovascular and respiratory diseases —  was higher in India than in any other country. In fact, Delhi topped the list of the worst polluted cities in the world, with an average annual exposure level of 110 μg/m3, followed by Kolkata with 84 μg/m3.

What is even more grim is that 90% of the world’s population experiences an average annual PM 2.5 concentration that consistently exceeds the World Health Organisation’s guideline of 10 μg/m3. Asian, African and Middle Eastern countries dominated the top five worst polluted countries list, which includes India (83.2 μg/m3), Nepal (83.1 μg/m3), Niger (80.1 μg/m3), Qatar (76 μg/m3) and then Nigeria (70.4 μg/m3), in order of most polluted to least.

Meanwhile, the cleanest countries were all first-world and high-income nations, and exhibited PM 2.5 concentrations of less than 8 μg/m3. Some of the cleanest countries include the US, Canada, Australia, New Zealand, Norway and Sweden.

The paper also lists trends in global ambient PM 2.5 exposure over the years, and it paints a horrible picture for South Asia. While global exposure has mostly remained the same, massive spikes in the pollutant has been observed most notably in South Asian as well as Sub-Saharan African countries between 2010 and 2019. Some of the most polluted countries in the world — India, Pakistan, and Bangladesh — continue to see increases over the years.

India tops the list in ozone increase

The study also monitored levels of ground-level ozone — a highly reactive pollutant that has serious effects on human as well as crop health. This is created in complex chemical reactions that stem mainly from fossil fuel burning in motor vehicles, power plants and industrial boilers, and can act as a greenhouse gas in warming the planet.

The WHO has set 50 ppb as a guideline for maximum ozone concentrations anyone should be exposed to for over 8 hours. All of the top ten worst ozone polluted countries exceed this mark, with India ranking at a sorrowful third on the list at 66.2 ppb.

The last time we exhibited levels somewhat close to the WHO standard was in 2010 with 56.5 ppb. Alarmingly, we have also had the largest jumps in ozone concentrations out of all the countries since then, with a massive 17% increase between 2010 and 2019. Ethiopia, Nigeria and Pakistan follow closely behind.

Household air pollution

One area where the government’s efforts to curb reliance on solid fuels such as kerosene, coal, charcoal and animal dung has paid off is in the household air pollution levels. According to the report, India has seen at least 54 million fewer people reliant on such fuel sources between 2010 and 2019, only trailing behind China in this regard.

South Asia has seen mostly a declining trend in reliance on solid fuel sources in the past decade, mainly due to aggressive campaigning to move towards cleaner fuel sources in the last few years. On the other hand, Sub-Saharan Africa has remained consistently at the top; in fact, all of the top ten countries most reliant on solid fuels hail from Africa.

Link between socioeconomic development and air pollution

Based on the data collected so far, it is evident that first-world countries continue to have lower air pollution levels than other nations. The study coined the Sociodevelopment Index (SDI) — a metric that measures the socioeconomic development of a country based on average income and educational attainment, among other factors.

It found that there is a moderate link between poor SDI and higher levels of exposure to PM 2.5. Scientists attribute this to the fact that PM 2.5 is a regional pollutant that can travel long distances and affect nearby countries, forming ”hotspots” of pollution.

Meanwhile, no correlation was found between the socioeconomic state of a country and its ozone pollution levels. Since large levels of ozone pollution have been detected in the high-income Middle East countries, the study attributes this to the large presence of oil production industries in the area, as well as its meteorology.

However, household pollution levels did have a strong link with the SDI of a country, the study found. Since solid fuels are more easily attainable in nations with low socioeconomic development rates, they are the preferred fuel of choice there, which leads to high levels of household air pollution. Further, low SDI countries usually also lack the funds to invest in infrastructure that will provide clean energy to the people.

T​his report was published by the Health Effects Institute and can be accessed here.

**

For weather, science, space, and COVID-19 updates on the go, download The Weather Channel App (on Android and iOS store). It's free!