South Asia’s Toxic Skies Are Trapping Heat in the Atmosphere

A global analysis of more than three decades of atmospheric observations has identified South Asia’s mixture of desert dust and human-made pollution as a major source of regional atmospheric heating. The findings underline why climate models must account not only for the quantity of airborne particles, but also for their composition, absorption properties and regional interactions.

South Asia experiences some of the strongest climate effects associated with airborne particles, according to a new international study that maps how different aerosol mixtures influence atmospheric heating around the world.

Published in Atmospheric Environment, the research finds that South Asia experiences some of the strongest atmospheric heating associated with aerosols, tiny airborne particles originating from desert dust, vehicle emissions, industry, forest fires and other sources. The study was led by Swagata Mukhopadhyay, Dr Shantikumar Singh Ningombam and Dr Umesh Chandra Dumka, with researchers from the Indian Institute of Astrophysics, the Aryabhatta Research Institute of Observational Sciences and several international institutions.

Across South Asia, desert dust frequently mixes with human-made pollution, creating an aerosol combination that absorbs solar energy and heats the atmosphere more strongly than many other particle mixtures found around the world. The discovery sharpens an important climate question: it is not simply how much pollution is in the air, but what that pollution contains and what it becomes when different particles interact.

When Dust and Pollution Become More Than Their Parts

Aerosols can affect the climate in contrasting ways. Some scatter sunlight back into space, reducing the amount of solar energy reaching the Earth's surface. Others absorb radiation, warming the surrounding atmosphere. Their influence depends on their size, composition, origin and ability to absorb or reflect light.

South Asia stands out because its atmosphere often contains particles from both natural and human-made sources. Dust carried from dry and desert regions can mix with pollution generated by transport, industrial activity and other forms of combustion. The study identifies these dust-dominated mixtures as the most common aerosol category across the region.

More importantly, these mixtures produce South Asia's highest aerosol radiative forcing and atmospheric heating rates. Aerosol radiative forcing measures how particles change the balance of energy within the Earth-atmosphere system. The stronger the absorption of sunlight, the more energy is retained in the atmosphere.

This does not mean aerosols alone determine regional temperatures, rainfall or storms. Weather systems are shaped by numerous interacting forces. But atmospheric heating can affect cloud development, air circulation and the distribution of energy at different altitudes, making aerosol composition an important part of understanding regional climate behaviour.

The findings also expose a difficult policy reality. Governments may be able to regulate vehicle exhaust, industrial emissions and other human-made pollutants, but they cannot manage desert dust in the same way. Once dust and pollution combine, however, their climate effects can no longer be assessed as entirely separate problems.

A Global Map Reveals a Deep Regional Divide

The research draws on more than 30 years of observations from 171 AERONET monitoring stations across six continents. AERONET is a global network of ground-based instruments used to measure the optical properties of aerosols and improve the interpretation of satellite observations. Using these measurements, the researchers classified aerosols into seven categories: pure dust, dust-dominated mixtures, pollution-dominated mixtures, very weakly absorbing, weakly absorbing, moderately absorbing and strongly absorbing aerosols.

The resulting map demonstrates that there is no single global aerosol problem. Different regions have distinct particle profiles shaped by their landscapes, economies and dominant emission sources. Pure dust is most prevalent in northern Africa. Europe and North America are largely characterised by less-absorbing urban and industrial aerosols. Tropical regions affected by biomass burning are dominated mainly by strongly absorbing particles. South Asia is distinguished by the widespread interaction between dust and pollution.

Climate models cannot treat all airborne particles as if they behave in the same way. A model that accurately captures aerosol concentrations but fails to represent their composition may still miscalculate how much sunlight is absorbed, how much reaches the surface and where atmospheric heating occurs.

The study provides more than a new classification system; it offers a framework for understanding why the same quantity of aerosols can produce sharply different climatic effects in different parts of the world.

Black Carbon Turns Dirty Air Into a Climate Force

Among the seven aerosol categories, strongly absorbing aerosols produced the greatest atmospheric warming. These particles, often rich in black carbon, generated average atmospheric forcing of 30.14 watts per square metre and the highest heating rates recorded in the analysis.

Black carbon is created through incomplete combustion and can be present in emissions from several sources. Its importance lies in its strong ability to absorb sunlight. Unlike particles that primarily reflect solar radiation, black carbon-rich aerosols transfer more energy directly into the atmosphere.

At the other end of the spectrum, very weakly absorbing aerosols produced the lowest atmospheric forcing. They reflected more sunlight and contributed considerably less to atmospheric heating.

The difference challenges the tendency to discuss air pollution as a single, uniform category. Particle counts and pollution concentrations remain important, especially for public health, but they do not reveal the complete climate impact. Two locations with similar aerosol levels could experience different atmospheric effects if their particles have different absorption properties.

For South Asia, this distinction has practical implications. Pollution-control measures may change not only the total quantity of aerosols but also their overall composition. Understanding which emissions contribute to the most strongly absorbing mixtures could eventually help scientists and policymakers evaluate air-quality and climate strategies more precisely.

Better Aerosol Science Could Rewire Climate Forecasting

The research could strengthen climate modelling, satellite remote sensing and air-quality monitoring by giving scientists a more detailed way to distinguish among aerosol types. Satellites provide broad geographical coverage, but interpreting what they observe from space can be difficult when particles overlap or possess similar visible characteristics. Ground-based measurements from networks such as AERONET can help scientists validate satellite data and identify whether particles are primarily dust, pollution, biomass-burning aerosols or complex mixtures.

More accurate classification could also improve estimates of atmospheric heating and help researchers study how aerosols interact with clouds, rainfall and regional circulation. For South Asia, this could be particularly relevant to efforts to understand climate and weather systems operating over one of the world's most densely populated regions.

However, classification is only the first step. The study's findings will need to be tested within regional climate models and combined with emissions inventories, satellite observations and local atmospheric data. Monitoring gaps may also remain in areas without long-term ground stations.