PM2.5 And PM10: How Different Air Pollution Particles Affect Your Health

Delhi's air quality deteriorated sharply on Monday, November 2, after a brief improvement following heavy rainfall last week. The national capital recorded an Air Quality Index (AQI) of 307 at 7.05 am, entering the ‘very poor’ category for the first time this season. Its 24-hour average AQI on Sunday was 261, against 60 on Friday.

However, the overall AQI is not the only cause for concern. Fine particulate matter, or PM2.5, has emerged as the principal pollutant across most of the city's monitoring stations, drawing attention to the health risks posed by the particles present in the air.

At 6 am on November 2, PM2.5 was the primary pollutant at 51 of Delhi's 58 monitoring stations reporting data. PM10 dominated at the remaining seven. On the previous day, PM2.5 had been the primary pollutant at 46 of 57 stations, reported News 18.

The difference between the two lies primarily in their size. This also determines how they enter the respiratory system and the extent of their potential impact on health.

Particulate Matter

According to the California Air Resources Board, particulate matter (PM) is a mixture of airborne solid particles and liquid droplets rather than a single pollutant. Its composition can include metallic compounds, inorganic ions, elemental carbon, organic substances and material from the earth's crust.

For air quality monitoring, these particles are classified by diameter. PM10 refers to particles measuring 10 micrometres or less, while PM2.5 comprises particles measuring 2.5 micrometres or less.

An important distinction is that PM2.5 forms part of the PM10 category. The latter includes both fine and coarser particles, whereas PM2.5 refers specifically to the finer fraction.

How Do PM2.5 And PM10 Differ?

Their sources also vary. PM2.5 is largely associated with combustion processes, including the burning of petrol, oil, diesel and wood. Motor vehicle exhaust and industrial emissions also contribute to its presence in outdoor air.

PM10 has a wider range of sources. Construction activity, agricultural operations, landfills, waste burning, wildfires and wind-blown dust all contribute to its concentration. Pollen and fragments of bacteria are also included in this category.

Particulate matter can enter the atmosphere directly from these sources or develop through chemical reactions involving gases such as sulphur dioxide (SO2) and nitrogen oxides (NOx). These reactions produce what are known as secondary particles. Natural sources, including trees and vegetation, can also contribute to their formation.

Is PM2.5 More Dangerous Than PM10?

The smaller diameter of PM2.5 allows these particles to travel deeper into the lungs than their coarser counterparts. They can reach the deepest parts of the respiratory system and enter the bloodstream, exposing other parts of the body to their effects.

Long-term exposure has been linked to aggravated asthma, impaired lung function, respiratory infections, chronic obstructive pulmonary disease (COPD), cardiovascular diseases and premature deaths.

The World Health Organization (WHO) has classified outdoor air pollution and particulate matter as carcinogenic to humans. These risks are not confined to people with existing illnesses; prolonged exposure can also affect otherwise healthy individuals.

PM10, though comparatively less capable of penetrating deep into the lungs, can irritate the eyes, nose and throat and worsen existing respiratory conditions.

The health implications have also prompted questions about India's pollution control priorities. Congress leader and former Environment Minister Jairam Ramesh has criticised the National Clean Air Programme (NCAP) for placing considerable emphasis on reducing PM10, arguing that PM2.5 deserves greater attention because of its health consequences.

Citing an analysis of 238 Indian cities, Ramesh had said that 204 recorded PM2.5 levels above India's National Ambient Air Quality Standards, while none met the WHO's recommended guidelines.

The government, meanwhile, has cited progress under NCAP. In a written reply to Parliament in July 2026, the Environment Ministry said 108 of the 130 cities covered under the programme recorded lower annual PM10 concentrations in 2025-26 than in 2017-18. Of these, 65 met the national PM2.5 standard.

Delhi's annual average PM2.5 concentration, however, stood at 102 micrograms per cubic metre, against the national annual standard of 40 micrograms per cubic metre.

Delhi's AQI And Residents

The CPCB categorises an AQI between 301 and 400 as ‘very poor’, a level at which prolonged exposure can cause respiratory discomfort and increase the risk of illness.

On November 2, 36 of Delhi's 58 reporting monitoring stations recorded very poor air quality. Jahangirpuri registered an AQI of 417, placing it in the severe category.

Children, senior citizens and people with respiratory or cardiovascular conditions face particular risks. Winter conditions, including lower temperatures and slower wind speeds, can further aggravate the situation by trapping pollutants closer to the ground.

Vehicular emissions, construction dust, industrial activity, biomass burning and agricultural fires add to the pollution load. With Diwali approaching, firecracker emissions could further increase particulate matter concentrations if unfavourable weather conditions persist.

For residents, limiting prolonged outdoor exertion during pollution episodes, following official health advisories and wearing appropriately fitted particulate-filtering masks when outdoor exposure is unavoidable can help reduce exposure.