Indoor Air Pollution: Sources, Health Effects and Solutions

Sources fall into four practical groups, and most buildings carry traces of all four.

Building fabric and finishes. Paints, adhesives, MDF, laminate flooring, foam insulation and soft furnishings release formaldehyde, benzene, toluene and a long tail of semi-volatile organics — highest in the weeks after installation, continuing at lower rates for years.

Occupant activity. Cooking is the largest indoor source of PM2.5 in most homes. Cleaning chemistry releases VOCs; printers generate ozone and ultrafine particles; candles and wood stoves add particulate and PAHs. Occupants themselves emit CO₂ and bioeffluents.

Building services. Poorly maintained HVAC recirculates dust, harbours microbial growth in coils and drip trays, and concentrates outdoor pollution when intakes are badly placed. Gas hobs and unflued heaters inject NO₂ and CO directly into living spaces.

The outdoor environment. Urban traffic, construction and seasonal wildfires deliver PM2.5, NO₂ and ozone through intakes and every leakage path. In UK cities, outdoor air sets the baseline indoor particulate level before any indoor source is added.

Useful monitoring focuses on a manageable set of indicators rather than chasing every compound.

PM2.5 and PM10. Fine particles penetrate deep into the alveoli and cross into the bloodstream. The WHO 2021 annual guideline of 5 µg/m³ is a public health target; most UK buildings sit well above it. PM2.5 deep-dive →

Carbon dioxide. The most useful single indicator of how diluted the rest of the indoor air mixture is. Above 1000 ppm cognitive performance suffers; above 1500 ppm intervention is warranted. More on CO₂ →

Volatile organic compounds. A TVOC reading under 300 µg/m³ is a reasonable target; speciated analysis is needed when specific compounds are suspected. VOCs in buildings →

Humidity. Relative humidity outside 40–60% drives microbial growth and respiratory irritation. Humidity and health →

NO₂, formaldehyde and radon belong on the watchlist for any building with combustion appliances, recent fit-out work or known geology risk.

Acute effects appear within hours: headache, eye and throat irritation, drowsiness, exacerbation of asthma, and the cluster of symptoms collected under sick building syndrome. They typically resolve on leaving the building — a useful diagnostic clue.

Chronic effects accumulate over years. Long-term PM2.5 exposure is linked to cardiovascular disease, lung cancer and reduced life expectancy. Repeated VOC exposure is associated with respiratory inflammation, and for benzene and formaldehyde with carcinogenic risk. Damp and mould increase asthma incidence in children and chronic rhinosinusitis in adults.

Vulnerable groups carry disproportionate risk: children breathe more air per kilo of body weight, the elderly and cardiopulmonary patients respond more sharply to spikes, and chronic particulate exposure has documented effects on birthweight.

The cognitive dimension is now evidence, not speculation. The Harvard COGfx studies measured double-digit drops in decision-making performance as CO₂ rose from 600 to 1400 ppm. For knowledge work, indoor air is a productivity variable.

A credible investigation combines continuous monitoring with grab samples and laboratory analysis. Continuous sensors capture CO₂, PM, temperature and humidity at minute-by-minute resolution. Sorbent tubes draw air across an absorbent medium so the lab can speciate VOCs by thermal desorption GC-MS.

Mould investigations add surface tape lifts, bulk samples and viable air sampling. Radon screening uses passive detectors over three months for seasonal variation. Ventilation effectiveness is assessed with CO₂ tracer-gas decay or direct airflow measurement at terminals.

Position matters as much as instrument choice. Sensors in the breathing zone at occupied desks tell a different story to those near supply diffusers. IAQ testing methodology →

Effective remediation follows an occupational-hygiene hierarchy.

Source control first. Substituting low-emission materials, switching cleaning chemistry, venting cooking and printing locally, and removing damp at source delivers more per pound than any downstream measure.

Ventilation second. Increasing outdoor air supply dilutes whatever source-control could not eliminate. CIBSE Guide A and BS EN 16798-1 set the design framework; demand-controlled ventilation tied to CO₂ sensors is the most efficient delivery method.

Filtration third. ISO ePM1 50% (≈ MERV 13) is the recommended grade for urban offices. Activated carbon stages add VOC and odour removal. HVAC and air quality →

Verification closes the loop. Re-measurement after intervention is non-negotiable — without it, remediation is faith-based engineering.

UK practice draws on a layered set of references: the Workplace (Health, Safety and Welfare) Regulations 1992 and ACOP L24 establish the duty to provide effective ventilation; CIBSE Guide A and TM40 give detailed design and operational guidance; BS EN 16798-1 sets indoor environmental categories for non-residential buildings; WHO global air quality guidelines provide the health-based reference points.

Voluntary frameworks add depth. WELL and BREEAM both reward credible IAQ monitoring and material selection; RESET Air specifies what continuous monitoring looks like at sensor, network and reporting level. More on workplace compliance →