Maarg Manthan · Topic 13.9

Respirable Suspended Particulate Matter (RSPM) and Fly Ash

Environment & Ecology › Air, Marine, Noise and Other Pollution · Topic 13.9

Suspended particulate matter (SPM) is the mixture of tiny solid and liquid particles floating in air. Respirable suspended particulate matter (RSPM) refers to the part small enough to be breathed deep into the lungs, in Indian usage particles up to 10 micrometres in diameter (PM10), including the finer PM2.5 fraction. Sources are vehicle exhaust, coal burning, industry, construction and road dust, crop residue and biomass burning, and secondary particles formed from SO2, NOx and ammonia. Particles cause asthma, bronchitis, heart and lung disease and cancer, reduce visibility and affect climate. The Indian ambient standards (NAAQS 2009) are 60 micrograms per cubic metre annual and 100 for 24 hours for PM10, and 40 and 60 for PM2.5. Fly ash is the fine residue carried out with flue gases when coal burns in power plants; coarser bottom ash falls to the base of the furnace. India generates a very large quantity of ash, more than 200 million tonnes a year; check the Central Electricity Authority data. Fly ash is used in cement, bricks, roads and mine fill, but ash ponds can pollute air, water and land.

5 min read · UPSC Prelims · Environment & Ecology · Air, Marine, Noise and Other Pollution

At a Glance

RSPM size Up to 10 micrometres
Fine fraction PM2.5
PM10 annual limit 60 micrograms per cubic metre
Fly ash source Coal power plants
Main use Cement and bricks
Exam link UPSC Prelims, Environment & Ecology: Air, Marine, Noise and Other Pollution

Where Does It Fit?

This topic follows the account of smog and acid rain and focuses on particles, the most health-damaging air pollutant. It prepares for the topics on vehicle emission norms and air quality indices. Previous topic: Smog, Ozone Depletion and Acid Rain. Next topic: Bharat Stage Emission Norms.

What Are RSPM and Fly Ash?

Term	Meaning and facts
SPM	All solid and liquid particles suspended in air, older measure including particles up to about 100 micrometres
RSPM (PM10)	Particles up to 10 micrometres that can be inhaled into the respiratory tract
PM2.5	Fine particles up to 2.5 micrometres that reach deep lung tissue and bloodstream
Primary particles	Directly emitted dust, soot and ash
Secondary particles	Formed from gases such as SO2, NOx, ammonia and VOCs
Fly ash	Fine ash carried by flue gas from coal-burning boilers and captured by precipitators
Bottom ash	Coarser ash falling to the bottom of the furnace

What Are the Effects, Standards and Uses of Fly Ash?

Health: particles cause lung and heart disease, cancer and early death
NAAQS PM10: 60 micrograms per cubic metre annual and 100 for 24 hours
NAAQS PM2.5: 40 micrograms per cubic metre annual and 60 for 24 hours
Fly ash generation: India produces more than 200 million tonnes of coal ash a year
Uses: cement and concrete, bricks and blocks, road and embankment fill, mine void filling, soil conditioner
Fly ash notification: Environment Ministry notification of 1999, updated several times, requires use of fly ash products near coal plants
Ash ponds: ash slurry stored in ponds can leak or breach and pollute water and air
Controls: electrostatic precipitators, bag filters, dust suppression and green belts

What Else Should You Remember?

Micrometre: one-millionth of a metre; a human hair is about 70 micrometres thick
Size and health: smaller particles go deeper, so PM2.5 is more harmful
Ultrafine particles: below 0.1 micrometre, can enter blood
Soot: black carbon from incomplete combustion
Composition: particles may carry metals, acids, organic compounds and allergens
PM sources in Delhi: vehicles, dust, industry and biomass burning, with seasonal variation
Crop residue burning: a seasonal source of PM2.5 in north India in October and November
Monitoring: measured by instruments such as high volume samplers and beta attenuation monitors
Visibility: particles scatter light and reduce visibility
Climate: some particles cool by reflecting sunlight, and black carbon warms
Fly ash content: mostly silica, alumina and iron oxides with traces of heavy metals
Pozzolanic: fly ash reacts with lime and water to form cement-like compounds
Fly ash bricks: use less clay and energy than burnt clay bricks
Portland pozzolana cement: cement with fly ash
Ash utilisation: official data show that most ash produced is now used, though old ponds hold large stocks
Legacy ash: stocks stored in old ponds remain a hazard
Ash pond breaches: have occurred at plants in Madhya Pradesh, Uttar Pradesh and Odisha
Fly ash and agriculture: limited use as soil amendment with care for metals
Coal quality: Indian coal has high ash content, often 30 to 45 percent
Washed coal: reduces ash going to power plants
ESP: electrostatic precipitators remove over 99 percent of fly ash from flue gas when working well
Fly Ash Utilization Mission: 1994 mission under the Department of Science and Technology
Link to previous: see Smog, Ozone Depletion and Acid Rain
Link to next: see Bharat Stage Emission Norms
Link to health: see Causes and Harmful Effects of Air Pollution
Caution: ash quantity and utilisation numbers change yearly, so use the latest CEA report
Exam hint: remember the size classes, the NAAQS values and the main uses of fly ash

Why Does It Matter for the Exam?

RSPM: Up to 10 micrometres
Deeper: PM2.5
Ash use: Cement, bricks
Current affairs link: Ash pond safety
Common errors: confusing fly ash with bottom ash

As an analytical point, fly ash shows how a waste can become a resource when rules and markets support it, but legacy ponds still need safe closure. For particles, source control at power plants, vehicles and farms matters more than urban dust control alone.

Why Is This Topic Important?

Size Smaller is deeper
Source Fuel, dust
Ash Resource

What Came Next?

The next topic covers Bharat Stage emission norms. Next topic: Bharat Stage Emission Norms.

Key People and Terms

RSPM Respirable suspended particulate matter
PM10 Particles up to 10 micrometres
PM2.5 Particles up to 2.5 micrometres
Fly ash Coal flue residue
ESP Electrostatic precipitator
Pozzolana Cement-like ash material

Exam Corner

Points to Remember

RSPM is up to 10 micrometres.
PM2.5 goes deepest.
PM10 annual limit: 60.
Fly ash notification: 1999.
ESP removes fly ash.

Do Not Confuse With

Fly ash and bottom ash Carried in gas versus falling in furnace
PM10 and PM2.5 Inhalable versus fine particles
SPM and RSPM All particles versus respirable size

Memory Hook

Ten for the nose, two-five for the blood; ash from coal makes bricks and cement.

Mains Angle

Questions ask for definitions and uses. These points help.

RSPM Source, health
Fly ash Waste to resource
Gaps Ponds

A Question You May Face

An original practice question, not a past paper question.

“What are RSPM and fly ash? Discuss their sources, effects and management in India.”

How to Answer

Define RSPM, ash.
Effects Health.
Uses Cement.
Gaps Ponds.

GS Relevance

Prelims: PM size, standards, fly ash uses. GS Paper 3: particulate pollution and waste utilisation.

Frequently Asked Questions

What is respirable suspended particulate matter?

Respirable suspended particulate matter, or RSPM, is the fraction of particles in air small enough, up to 10 micrometres in diameter in Indian usage, to be inhaled into the lungs. It is also called PM10 and includes the finer PM2.5. Sources include vehicles, industry, coal burning, dust and biomass burning, and it causes respiratory and heart disease.

Why is PM2.5 more dangerous than PM10?

PM2.5 particles are so small that they bypass the nose and throat defences and reach the deepest parts of the lungs, where some pass into the bloodstream. They carry toxic substances and are linked with heart disease, stroke, lung cancer and early death, so health guidelines and standards are stricter for PM2.5.

What is fly ash?

Fly ash is the fine powdery residue that is carried out of a coal-fired boiler with the flue gas and captured by electrostatic precipitators or filters. It is mostly silica, alumina and iron oxides, and may contain traces of metals. Coarser ash that settles at the bottom of the furnace is called bottom ash.

How is fly ash used?

Fly ash is used as a substitute for part of cement in concrete and Portland pozzolana cement, in making bricks and blocks, as filler in road and embankment construction, to fill mine voids, and in limited cases as soil amendment. The Environment Ministry's fly ash notification requires use of fly ash products near coal power plants.

What are the problems with fly ash ponds?

Fly ash ponds take up land and can leak or breach, polluting rivers, soil and groundwater with fine ash and metals. Dry ash blows as dust and affects air quality and health. Legacy ash stocks remain from older plants, so safe disposal, higher utilisation and proper pond closure are needed.

PYQ Practice — Statement Analysis

1 RSPM refers to particles of up to 10 micrometres.

True

PM10.

2 Fly ash falls at the bottom of the furnace.

False

That is bottom ash.

3 Fly ash is used in cement and bricks.