Particulate matter

Particulate matter (PM) acts like an invisible dust storm of microscopic solid particles and liquid droplets drifting through our homes, schools, and offices. Ranging in size from a few nanometres to tens of micrometres, these airborne particles are categorized by their aerodynamic diameter: coarse particles (PM10, smaller than 10 µm), fine particles (PM2.5, smaller than 2.5 µm), and ultrafine particles (UFPs, smaller than 100 nm). Particle size and chemical composition dictate how long they stay airborne and how deeply they penetrate into the human respiratory system.

Why Measure Particulate Matter?

Breathing in particulate matter poses significant health risks even at very low concentrations, with no recognized threshold below which no health damage occurs.

• Coarse particles (PM10) are typically trapped in the upper airways, causing irritation of the eyes, nose, and throat, as well as triggering allergic rhinitis and asthma symptoms.
• Fine and ultrafine particles (PM2.5 and UFPs) pass deep into the bronchioles, cross the alveolar air-blood barrier, and enter the bloodstream, driving cardiovascular diseases, systemic inflammation, chronic obstructive pulmonary disease (COPD), and lung cancer.

How to Measure Particulate Matter

Assessing particulate matter effectively requires a combination of monitoring approaches:

• Low-cost sensors (LCS): Deploy optical particle counters capable of measuring mass concentrations in real time to track daily exposure patterns. Position sensors at breathing height (1.0 to 1.5 m from the floor), keeping them away from direct airflow drafts from windows, radiators, and localized pollutant sources.
• Reference instrumentation: For high-precision research, advanced systems such as Scanning Mobility Particle Sizers (SMPS) and Optical Particle Size Spectrometers (OPSS) measure particle number size distributions across nanometre and micrometre ranges.

What is the Issue? Differentiating Indoor and Outdoor Sources

Indoor particulate concentrations are shaped by a complex mix of infiltrating outdoor pollution and internal generation activities.

Outdoor Infiltration

Outdoor air pollution—primarily driven by vehicular exhaust, road dust resuspension, industrial emissions, and regional biomass burning—infiltrates buildings through open windows, doors, and building envelopes. In urban schools located near heavy traffic corridors, outdoor fine particles and black carbon are major contributors to indoor pollution levels.

Indoor Activities and Occupant Behavior

Inside buildings, daily human activities generate substantial particle loads:

• Cooking and heating: Frying, roasting, and using unvented gas cookers or biomass stoves release large bursts of fine and ultrafine particles.
• Resuspension: Movement by occupants and cleaning activities resuspend settled dust from floors and carpets. In schools, particulate matter (PM2.5 and PM10) is frequently dominated by indoor sources, notably the resuspension of dust and soil brought inside on children's shoes and clothing.
• Surface emissions: Burning candles, incense, smoking tobacco products, and operating laser printers or photocopiers generate significant secondary aerosols and particle number concentrations.

[+] Click here to view technical details: Particle dynamics, metrology, and deposition models

Particle size and chemical composition influence atmospheric transport, coagulation, deposition, and toxicological potency. The combination of size spectrometers (such as MPSS and OPSS) allows researchers to derive particle mass size distributions (PMSD) using assumed particle densities and integration cut-offs. Furthermore, regional respiratory tract deposition models calculate the precise alveolar and tracheobronchial doses absorbed during human inhalation across varying activity levels and age groups, supporting advanced epidemiological and toxicological evaluations within the EDIAQI framework.

What Now? Practical Mitigation and Control

Managing particulate matter exposure relies on targeted engineering and behavioral interventions:

• Source control: Ban indoor smoking, substitute high-emission cleaning products with fragrance-free ecolabel alternatives, and isolate combustion activities.
• Ventilation management: Always operate ducted cooker hoods during cooking. In schools and offices, flush stale air by opening opposite windows for five to ten minutes between classes or meetings.
• Entryway hygiene: Implement shoe-removal policies at building entrances to significantly reduce the influx and subsequent resuspension of tracked-in soil and dust.
• Filtration and air cleaning: Ensure mechanical ventilation systems are equipped with high-efficiency particulate air (HEPA) filters, and deploy certified portable air cleaners in rooms exposed to heavy traffic or high occupancy.