Science-Backed Educational Guide

PM2.5 Explained

PM2.5 refers to tiny particles smaller than 2.5 micrometres - about 30 times thinner than a human hair. These particles are small enough to enter your bloodstream.

What Does PM2.5 Mean?

PM stands for Particulate Matter - tiny solid particles or liquid droplets suspended in the air.

2.5 refers to the particle diameter in micrometres (µm). PM2.5 particles are 2.5 µm or smaller - invisible to the naked eye.

Why PM2.5 Is Dangerous

Unlike larger particles that your nose and throat filter out, PM2.5 particles are small enough to bypass your body's defences, enter your lungs, and pass directly into your bloodstream.

Size Comparison

Human hair70 µm28x larger than PM2.5

Grain of sand90 µm36x larger than PM2.5

PM10 particle10 µm4x larger than PM2.5

PM2.5 particle2.5 µmBaseline

Bacteria1-5 µmSimilar to PM2.5

Virus0.1 µm25x smaller than PM2.5

Health Effects of PM2.5

Long-term PM2.5 exposure is linked to 4.2 million premature deaths globally each year (WHO 2024). Here's how it affects different parts of your body:

Lungs

• Aggravated asthma
• Reduced lung function
• Chronic bronchitis
• Increased respiratory infections

Heart

• Irregular heartbeat
• Heart attacks
• Increased blood pressure
• Cardiovascular disease

Brain

• Cognitive decline
• Increased dementia risk
• Stroke risk
• Neuroinflammation

Eyes

• Eye irritation
• Watery eyes
• Conjunctivitis
• Long-term damage

PM2.5 Levels Guide (µg/m³)

0-12

Good

Air quality is satisfactory

12-35

Moderate

Acceptable for most people

35-55

Unhealthy for Sensitive

Sensitive groups should limit exposure

55-150

Unhealthy

Everyone may experience effects

150-250

Very Unhealthy

Health warnings for all

250+

Hazardous

Emergency conditions

WHO Guideline (2021): Annual average should not exceed 5 µg/m³, with 24-hour average below 15 µg/m³. The UK currently follows less strict EU standards of 25 µg/m³ annual average.