What is particulate matter?-Everything you need to know

Let’s go in detail about Particulate Matter (PM), especially in the context of automobile emissions.

1. What is Particulate Matter (PM)?

Definition:
Particulate Matter (PM) refers to tiny solid or liquid particles suspended in the air. In automobiles, PM mostly comes from incomplete combustion of fuel, especially diesel.

Characteristics:

Size: Ranges from coarse particles (>2.5 µm) to fine particles (<2.5 µm, PM2.5) and ultrafine particles (<0.1 µm).
Composition: Carbon (soot), hydrocarbons, metals, sulfates, nitrates, and ash.
Visibility: Can appear as black smoke from diesel engines.

2. Formation of Particulate Matter in Vehicles

A. Diesel (CI) Engines

Main source of PM because diesel burns fuel under high compression but lean mixture.
Incomplete combustion → carbon soot, adsorbed unburnt hydrocarbons, and sulfates.
PM increases under:
- Low-speed operation
- High load
- Cold start
- Poor fuel atomization

B. Petrol (SI) Engines

PM is much lower, but direct injection engines can emit ultrafine particles.

C. Evaporative PM

Fuel evaporation and lubricating oil burning also contribute to PM.

3. Types of Particulate Matter

Type	Size	Source	Remarks
Coarse PM (PM10)	2.5–10 µm	Road dust, tire wear	Settles quickly, affects air quality
Fine PM (PM2.5)	<2.5 µm	Diesel combustion, gasoline direct injection	Can penetrate lungs deeply
Ultrafine PM (PM0.1)	<0.1 µm	Vehicle exhaust, nanoparticles	Can enter bloodstream, highly toxic
Black Carbon (Soot)	Variable	Diesel engines	Main contributor to global warming & air pollution

4. Environmental and Health Effects

A. Health Effects

Respiratory: Asthma, bronchitis, lung inflammation
Cardiovascular: Heart attacks, stroke
Chronic exposure: Lung cancer, reduced lung function
Ultrafine PM: Can cross lung membranes and affect brain, heart, and kidneys

B. Environmental Effects

Air pollution: Reduces visibility (smog, haze)
Climate impact: Black carbon absorbs sunlight → global warming
Soil & water contamination: Settles on surfaces and water bodies

5. Control of Particulate Matter in Automobiles

A. Engine Design

Better fuel atomization: Complete combustion → fewer soot particles
Optimized injection timing: Reduces incomplete combustion
Turbocharging and intercooling: Lower PM emissions

B. After-Treatment Devices

Diesel Particulate Filter (DPF)
- Traps PM from exhaust gas.
- Periodically burns collected soot at high temperatures (regeneration).
- Can reduce PM by up to 90–99%.
Catalytic Converters
- Oxidizes some hydrocarbons and soot → CO₂ + H₂O
- More effective in gasoline engines

C. Fuel Quality

Low-sulfur diesel → reduces sulfate PM formation
Biodiesel blends → can reduce PM but may increase NOₓ slightly

6. PM in SI vs CI Engines

Pollutant	SI Engine (Petrol)	CI Engine (Diesel)	Notes
PM (Soot)	Low	High	Diesel engines produce visible black smoke
PM2.5 / PM0.1	Low	High	Ultrafine particles harmful to lungs
Source	Evaporation, misfire	Incomplete combustion, fuel-rich pockets

7. Typical PM Levels

Engine Type	Without Control	With DPF / Catalytic Converter
Diesel CI	0.1–0.3 g/km	0.004–0.01 g/km
Petrol SI	0.005–0.01 g/km	<0.005 g/km

8. Key Facts

PM is not a single chemical, but a mixture of soot, hydrocarbons, metals, and sulfates.
Diesel engines are the largest source in transportation.
Health risk increases with particle size decrease → PM0.1 more dangerous than PM10.
DPF regeneration requires proper driving conditions; otherwise soot buildup can damage the filter.

9. Summary Table

Aspect	Details
Definition	Tiny solid or liquid particles from combustion
Chemical Composition	Carbon, hydrocarbons, metals, sulfates
Major Source	Diesel engines, fuel combustion
Health Effects	Respiratory, cardiovascular, cancer
Environmental Effects	Smog, global warming, soil/water contamination
Control Measures	Diesel Particulate Filter, Catalytic Converter, low-sulfur fuel, engine optimization

In Short:

Particulate Matter (PM) is a mixture of soot, hydrocarbons, and other particles emitted mainly from diesel engines.
It pollutes air, damages human health, and contributes to global warming, but DPFs, catalytic converters, and cleaner fuels can drastically reduce PM emissions.

💡 Fun Fact:
A single modern diesel car without a DPF can emit billions of ultrafine particles in just one kilometer of driving!

FAQ Section:

Here are 10 frequently asked questions (FAQs) about Particulate Matter (PM):

What is Particulate Matter (PM)?
Particulate Matter is a mixture of tiny solid particles and liquid droplets suspended in the air, such as dust, soot, and smoke.
What are the types of Particulate Matter?
PM is classified mainly by size: PM10 (particles ≤10 micrometers) and PM2.5 (particles ≤2.5 micrometers).
How is PM produced?
PM is produced from vehicle exhaust, industrial emissions, construction dust, burning of fossil fuels, and natural sources like pollen or wildfires.
Why is PM harmful to health?
Fine particles can penetrate lungs and bloodstream, causing respiratory problems, heart disease, and aggravating asthma.
Does PM affect the environment?
Yes, it contributes to air pollution, reduced visibility, acid rain, and climate effects.
How do vehicles contribute to PM?
Diesel engines, incomplete combustion, and tire or brake wear release soot and fine particles into the air.
Can PM be controlled or reduced?
Yes, using filters (like Diesel Particulate Filters), cleaner fuels, emission controls, and dust suppression methods can reduce PM emissions.
Is PM only a human-made pollutant?
No, PM can also come from natural sources such as volcanoes, dust storms, pollen, and sea spray.
How is PM measured?
PM is measured using air quality monitoring stations, filters, and specialized sensors to determine particle concentration in the air.
Why is PM2.5 more dangerous than PM10?
PM2.5 particles are smaller, can penetrate deeper into the lungs, enter the bloodstream, and cause more severe health effects.