India: Burning Plastics Increases Smog

You probably know that plastic waste is increasingly polluting our oceans but new data shows that plastic is also contributing to the rampant air pollution in Indian cities.

Scientists were puzzled why Delhi was more susceptible to thick smogs than other polluted cities such as Beijing. New research links this to tiny chloride particles in the air that help water droplets to form[1]. Globally, chloride particles are mainly found close to coasts, due to sea spray and carried some distance inland by the wind, but the air in Delhi and over inland India contains much more than expected.

At first, the sources were thought to be illegal factories around Delhi that recycle electronics and those that use strong hydrochloric acid to clean and process metals. These are certainly part of the problem, but new measurements have revealed another source.

Other researchers looked at the other pollutants that increased at the same time as the chloride particles. This chemical fingerprint matched the burning of household waste containing plastics and the burning of plastics themselves. These large amounts of chloride are estimated to be responsible for around half of Delhi’s smog events. Episodic hourly averaged chloride concentrations reached 50–100 µg m⁻³, ranking among the highest chloride concentrations reported anywhere in the world.

In low-income countries about 90% of waste ends up in open dumps or is burned in the open air. If you set fire to plastic, it rapidly reveals its origins as an oil-based product by producing huge amounts of black smoke. Using data on the contents of rubbish from around the world, researchers estimated that the soot from open waste burning has a global warming impact equivalent to between 2% and 10% of the global emissions of carbon dioxide[2].

Burning plastics also produces large amounts of dioxins and other highly toxic pollutants that can persist in the food chain. Modern waste incinerators in the UK and Europe go to great lengths to reduce these toxic emissions but there are no protections when waste is burned at home or in the open air.

The problems of waste burning in Indian cities do not end there. As James Allan from the University of Manchester, who took part in the latest Indian study, explained, the extra chloride could be promoting chemical reactions between different air pollutants. This includes adding to the ground-level ozone across India. Already this is estimated to reduce yields of some Indian crops by 20% to 30%.

The solution to this problem seems easy: better waste management and an end to global plastic production and use.

[1] Gani et al: Submicron aerosol composition in the world's most polluted megacity: the Delhi Aerosol Supersite study in Atmospheric Chemistry and Physics – 2019. See here.
[2] Reyna-Bensusan et al: Experimental measurements of black carbon emission factors to estimate the global impact of uncontrolled burning of waste in Atmospheric Environment - 2019