Emma Gibbons conducted a study of indoor air quality in three modern office buildings in London. Continuous and passive monitoring was used to measure concentrations of pollutants like NO2 and PM2.5 both indoors and outdoors over periods of at least six months. The results showed outdoor pollutant levels were generally higher but indoor levels still exceeded WHO guidelines. Mechanically ventilated buildings with filtration had lower indoor PM2.5 levels. Potential mitigation strategies identified included improving outdoor air quality, optimizing building design and ventilation, and using air cleaning technologies. Next steps include further monitoring, analyzing results, and investigating smart ventilation and filtration options.

1. Indoor air quality study in
modern office buildings
Emma Gibbons
October 2023
INSTITUTE FOR ENVIRONMENTAL DESIGN & ENGINEERING
Work has been supported by CIBSE, and the Engineering and
Physical Sciences Research Council (EPSRC).
Supervisors: Dr Marcella Ucci, Dr Sam Stamp

2. Contents
01 Introduction
02 Case study buildings
03 Methodology
04 Results
05 Conclusions
06 Next steps

3. 01 Introduction
“Air Pollution is the top environmental risk to human health in the UK, and the fourth greatest threat to
public health after cancer, heart disease and obesity.” - Defra, Clean Air Strategy, 2019.
Public Health England, Guidance; Health matters: air pollution, Published 14 November 2018
https://www.gov.uk/government/publications/health-matters-air-pollution/health-matters-air-pollution
Indoor sources of air pollution

4. Research gaps
There is limited research into indoor
air pollutant concentrations and ingress
of ambient air pollution in city centre
offices.
Aim of study:
Understand how office buildings can be designed and operated
to reduce ingress of ambient air pollution, and what impact
building ventilation can have on indoor pollutant concentrations.

5. Case study building selection criteria:
• Buildings which are primarily offices.
• Buildings where the ventilation strategy of the
building is understood.
• Willingness of stakeholders (facility or building
managers) to be involved in the study.
• Buildings with different ventilation strategies.
• Buildings where monitoring can be carried out
indoors and outdoors simultaneously, for an
extended period (6 months plus).
02 Case study buildings

6. Case study building 1
• Six-storey office building in central London.
• Fully mechanically ventilated with no openable
windows.
• Air intake and air handling units (AHUs) located
at roof level.
• Air supplied to internal zones via active chilled
beams located in the ceilings.
• Building is located within an AQMA, declared
due to exceedances of PM10 (24-hr) and NO2
(annual) air quality objectives.

7. Case study building 2
• Ground floor office in central London.
• Fully mechanically ventilated with no
openable windows.
• Leaky façade.
• Air intake and air handling units (AHUs)
are located at basement level.
• Building is located within an AQMA,
declared due to exceedances of PM10
(24-hr) and NO2 (1-hr and annual) air
quality objectives.

8. Case study building 3
• Eight-storey office building in London.
• Naturally ventilated with openable
windows.
• Recently refurbished.
• Building is located within an AQMA,
declared due to exceedances of PM10
(24-hr) and NO2 (1-hr and annual) air
quality objectives.

9. • 22 air pollutants, plus comfort
parameters.
• Measurements using diffusive
(passive) sampling & continuous
monitoring methods.
• Continuous monitors co-located with
reference instruments prior to install.
• Continuous measurements taken
with 5 min averaging period.
• Discussions and semi-structured
interviews held with building teams.
03 Methodology

10. Pollutants measured
Nitrogen
dioxide
(NO2)
Carbon
dioxide
(CO2)
PM10,
PM2.5
and PM1
Ozone
(O3)
Carbon
monoxide
(CO)
Total
VOCs
Temp &
Relative
Humidity
Continuous
Passive
Nitrogen
dioxide
(NO2)
Ozone
(O3)
Speciated
VOCs
Form-
aldehyde
Speciated VOCs: Benzene, Toluene, Ethyl-benzene, o/m/p-xylenes,
Styrene, Naphthalene, n-Hexane, ɑ-Pinene, Limonene, Ethylhexanol,
2-Butoxyethanol, Trichloroethylene, Tetrachloroethylene, TVOCs.

11. Monitoring locations
• First case study building - 30 monitoring locations (13 continuous and 17 passive)
• Second case study building - 11 monitoring locations (5 continuous and 6 passive)
• Third case study building - 16 monitoring locations (5 continuous and 11 passive)
• Measurements taken indoors and outdoors simultaneously, at a height representative
of exposure (indoors) at ground level, roof level and at air inlet locations (outdoors).

12. 04 Results
• Passive NO2
• Continuous NO2
• Continuous PM2.5

13. Outdoor NO2 concentrations higher than indoors, but
concentrations at all locations are greater than long-term WHO
guideline value of 10µg/m3.
Passive NO2 – Case study building 1
Increased winter-time NO2 concentrations,
observed indoors and outdoors.

14. Outdoor NO2 concentrations higher than indoors, but indoor concs still
higher than WHO guideline value.
Passive NO2 – Case study building 2
Increased winter-time NO2 concentrations
all locations.

15. Outdoor NO2 concentrations higher than indoors, and indoor
concentrations lower than in the mechanically ventilated buildings.
Passive NO2 – Case study building 3
Increased winter-time NO2 concentrations
at outdoor locations, but not indoors.

16. • Measured PM2.5 concentrations outdoors are higher than indoors.
• Positive impact of the in-line particulate filters in the mechanically ventilated building.
Continuous PM2.5 – Case study building 1

17. • Measured PM2.5 concentrations outdoors are higher than indoors – effective filtration.
• Leaky building shows increase in concentrations overnight.
Continuous PM2.5 – Case study building 2
Average PM2.5
concentration
(µg/m3) at all
monitoring
locations
Average PM2.5
concentration
(µg/m3) at indoor
locations

18. Potential mitigation strategies
Source control
• Building managers have less influence over outdoor pollutants.
• Some cities are doing more to improve ambient air pollution.
Building design
• Consideration of ventilation and AQ early in design phase e.g. location
of air intakes, ventilation style and set up, integrated filtration.
Smart ventilation
• Closing windows on high-pollution days can reduce occupant exposure
(Dutton et al., 2013, and Martins and Carrilho da Graça, 2018).
• Mechanical systems set to operate during certain time periods, avoiding
peak pollution events.
Air cleaning technologies
• Stand-alone units, such as air purifiers.
• In-line filters in mechanical systems.
• Carbon filters can reduce indoor concentrations of NO2, and filter
efficiency can be around 70-90% (Ginestet and Pugnet, 2006).

19. Present and
disseminate
findings
Air quality
monitoring in
further case
study buildings
Review
possible
mitigation
strategies
Continue to
analyse data
from case study
buildings
06 Next steps
Possible mitigation strategies to investigate: smart ventilation / air cleaning technologies.
Do you work in or know of a building which has hybrid ventilation,
CO2 controlled ventilation or NO2 filtration?
Are you looking to implement any mitigation strategies to improve indoor air quality?

20. Thank you, any questions?
Emma Gibbons, BSc (Hons), CEnv, MIAQM, MIEnvSc, PIEMA
The Bartlett School of Environment, Energy and Resources
UCL Institute for Environmental Design and Engineering
Email: emma.gibbons.20@ucl.ac.uk
INSTITUTE FOR ENVIRONMENTAL DESIGN & ENGINEERING