PM2.5 or PM10? The Pollutant Behind India's AQI Can Change What You Need to Know About the Air You Breathe

PM2.5 and PM10 are categories of airborne particles measured by size. PM2.5 refers to particles up to 2.5 micrometres across. PM10 refers to particles up to 10 micrometres across. Because PM2.5 is smaller, it can penetrate farther into the respiratory system. The article identifies PM2.5 as the usual main culprit behind poor AQI readings.

The size difference is substantial. PM2.5 particles are about 30 times thinner than a strand of hair, according to the article. PM10 includes those finer particles as well as larger particles, such as some dust. Construction and road dust are among the pollution sources mentioned in the article.

The article focuses more heavily on PM2.5 than PM10 because fine particles often drive the AQI. The AQI uses eight pollutants, and the single worst pollutant sets the final number. This means a city can receive a Poor reading when PM2.5 is high, even if other pollutant measurements remain acceptable.

A reading of 244 means Delhi, or another Indian city, is experiencing Poor air quality on India’s 0-to-500 scale. Poor covers readings from 201 through 300. The scale is divided into six colour-coded categories, so 244 is well above Moderate and below Very Poor. Higher readings indicate rising health risk.

The number is not a simple average of all pollution measurements. India’s AQI summarises eight pollutants, and the single worst pollutant determines the result. PM2.5 is usually the main driver. Therefore, one particularly smoky or dusty pollutant reading can push the overall AQI to 244 even when other readings appear less concerning.

The article associates the Poor category with breathing discomfort after prolonged exposure. Citizens can check the pollutant driving the number on CPCB’s Sameer app or dashboard. That detail matters because it helps people judge whether masks, air purifiers, or staying indoors may make sense.

Delhi’s AQI rises when emissions accumulate faster than they disperse. Traffic fumes, construction and road dust, and smoke from burning waste provide continuing pollution. Cooler evenings and slower winds then allow these pollutants to build up near the ground. The result can be a sharp change in the city’s air-quality category.

The article gives a direct example: Delhi’s AQI climbed from 179 to 244. A reading of 179 is Moderate, while 244 is Poor. Crop-stubble burning in Punjab and Haryana, festival fireworks, and cold, still air can add further pollution. These sources do not need to act separately; their combined effect can worsen the reading.

Farm fires are not the whole explanation. A CREA analysis found they contributed less than 6% of Delhi’s fine-particle pollution in October. The AQI also depends on whichever pollutant is worst. Checking that pollutant through CPCB’s Sameer app or dashboard gives a clearer picture of what is driving the rise.

India’s AQI turns complicated pollution measurements into one number between 0 and 500. It uses eight pollutants and fixed health-based limits, allowing citizens to understand air quality quickly. The Central Pollution Control Board launched the system in September 2014. Six categories then translate the number into labels such as Poor, Very Poor, or Severe.

The AQI is a worst-case summary, not an average. Each pollutant’s reading is assessed against the relevant health-based limits. The pollutant producing the highest resulting risk determines the final AQI category. For example, a smoky day with especially high PM2.5 can produce a Poor reading even when the other pollutant measurements look fine.

This design makes the number more useful as a warning signal. It tells people that at least one pollutant has reached the reported risk level. PM2.5 is usually the main culprit, but citizens can check the actual driver on CPCB’s Sameer app or dashboard before deciding on precautions.

India’s AQI links rising numbers with increasingly serious health effects. Poor covers readings from 201 to 300. Very Poor covers 301 to 400. Severe covers 401 to 500. These categories show that risk does not stop with people who already have asthma or heart problems; it rises as pollution becomes more intense.

The article identifies specific consequences. Prolonged exposure during Poor conditions can cause breathing discomfort. Very Poor air can cause respiratory illness. Severe air affects healthy people and seriously impacts those with existing lung or heart disease. The higher category therefore signals both broader harm and greater urgency.

These effects are especially important during pollution episodes involving smoke, dust, and trapped air. Citizens can check the AQI and its driving pollutant on CPCB’s Sameer app or dashboard. That information can help people decide whether masks, air purifiers, or staying indoors are sensible responses to the day’s conditions.

Crop-stubble burning can contribute very different shares of Delhi’s fine-particle pollution. A CREA analysis found that farm fires in Punjab and Haryana contributed less than 6% of the city’s fine-particle pollution in October. That shows farm fires are important but are not automatically the dominant source during ordinary pollution periods.

During a much more extreme episode, Delhi’s AQI reached 418, in the Severe category. Stubble burning alone accounted for over 22% of the city’s fine-particle pollution. The larger share occurred alongside heavy farm fires, a Diwali night, and air trapped close to the ground. Those conditions added pollution and reduced dispersion.

The contrast shows why severe days are rarely caused by one factor. Traffic, dust, waste smoke, fireworks, farm fires, cold temperatures, and still air can all contribute. The final AQI still depends on the worst pollutant, so the source share and the headline AQI describe related but different aspects of the episode.

PM2.5 particles are especially concerning because they are extremely small: the article describes them as about 30 times thinner than a strand of hair. Their size allows them to travel deeper into the lungs than larger particles. PM10 is a broader category containing particles up to 10 micrometres across, while PM2.5 covers particles up to 2.5 micrometres. The deeper-lung explanation is established particle-health science beyond the article’s detailed discussion.

The article repeatedly identifies PM2.5 as the usual main culprit behind poor air readings. Smoke, traffic fumes, dust, fireworks, and farm fires can all add fine particles to the air. When PM2.5 becomes the worst pollutant, it can determine the entire AQI, even if other measurements look acceptable.

That matters because the health stakes rise with the AQI category. Poor air can cause breathing discomfort after prolonged exposure. Very Poor air can cause respiratory illness, while Severe air affects healthy people and seriously impacts those with existing lung or heart disease.