Particulates — PM2.5, PM10, PM1
Fine particulates are the most health-relevant office air pollutant. Urban offices on busy roads experience indoor PM2.5 that closely tracks outdoor — without adequate AHU filtration, the indoor environment is essentially a slightly filtered version of the street outside. ISO 16890 ePM1-rated filters at 50% or higher are the standard control.
Carbon dioxide — the ventilation proxy
CO₂ is generated by occupants and accumulates whenever ventilation is insufficient. At sustained levels above 1500 ppm, decision-making declines and headache complaints rise. CO₂ itself is non-toxic at office concentrations — its value is as the cleanest single proxy for ventilation effectiveness and for the co-pollutants that accumulate alongside it.
VOCs and formaldehyde
Volatile organic compounds from materials, cleaning products and electronics drive office odour complaints and post-refurbishment symptoms. Formaldehyde from composite wood furniture is the single most commonly detected office VOC at concentrations that matter.
NO₂ and outdoor infiltration
Urban offices in NO₂ hotspots (close to busy roads, near diesel parking) see indoor NO₂ closely tracking outdoor unless intakes are well-located and filtration is appropriate. Activated carbon on supply air handles most NO₂ infiltration where intake relocation is not feasible.
Controlling office air pollution
Control sequence: source removal (low-emission materials, intake relocation), filtration (ISO 16890 ePM1 plus activated carbon where needed), ventilation (BS EN 16798 Category II minimum, demand-controlled where appropriate), monitoring (continuous, dashboarded). In that order.
Frequently asked questions
Is office air really more polluted than outdoor air?
For most modern UK offices, indoor air is cleaner than outdoor — but the gap is smaller than people assume. Without ePM1 filtration, indoor PM2.5 is typically 60–80% of outdoor. With it, 15–30%.
Which office air pollutant is most dangerous?
PM2.5 is the most strongly health-linked indoor air pollutant in office settings. CO₂ is the most useful operational indicator. Formaldehyde and VOCs are the most common drivers of acute complaints.
How is office air pollution different from outdoor air pollution?
The pollutants overlap but indoor levels are dominated by the filtration and ventilation that separate inside from outside, plus indoor-generated sources (people, materials, cleaning, equipment) that have no outdoor equivalent.