Indoor and outdoor air pollution is responsible for 6·5 million deaths worldwide per year and Public Health England estimates that human-made air pollution causes up to 36,000 deaths per year in the UK1. In England, the total cost estimate to the NHS and social care between 2017 and 2025 could be as high as £5.6 billion2 with 2.5 million new cases of disease by 2035.
Outdoor air pollution includes particulate matter (PM2.5 and PM10) and whereas transport only contributes around 12% of the PM2.5 that we are exposed to, other major sources include residential homes, small commercial units and industry. PM2.5 can in fact be a very regional pollutant where pollution caused in one country can be blown by wind into other countries. Indoor air pollution is also an issue where households and the workplace contain hundreds of pollutants including PM2.5. Studies of human exposure to air pollutants by the U.S. Environmental Protection Agency indicate that indoor levels of pollutants are generally 2-5 times higher than outdoor levels3 which is a concern given that most people spend about 90% of their time indoors4.
It is estimated that around 800,000 people die each year due to poor air quality in the workplace with further health and wellbeing impacts affecting productivity and ultimately the economy5. In the UK, as specified in Section 6 of the 1992 Workplace Health, Safety and Welfare Regulations, companies have a legal obligation to ensure that workplaces have efficient ventilation and availability of fresh or purified air for the workforce6.
Despite current UK legislation, many small office spaces are located in older buildings that lack mechanical ventilation systems and depend on natural means such as opening a window. If a building is located close to heavy traffic or a source of increased PM2.5 emissions then there is a risk that opening a window could lead to an increase in particulate levels within the internal office air.
Interestingly, most studies on indoor air quality within the workplace have been carried out within larger office space in newer builds. Therefore, using portable continuous monitors, we have carried out research to assess PM2.5 in a small office environment supporting three staff in a brick 40-year old building a town centre with no building management system. The office space was 5m length x 5m width x 3m height rising to 7m at a ceiling apex. A single door to the office was left permanently open and the only other ventilation was a single ceiling Velux window that required manual opening and closing. Temperature and humidity were measured using an Elsys ERS Lite LoRaWAN enabled internal sensor placed centrally at desk level in the room. Data were retrieved each minute over a three week period to a ThinkAir cloud database via a Kerlink Wirnet iFemtoCell LoRaWAN gateway.
PM2.5 data were averaged every 15 minutes over an 8 day period using a ThinkAir internal air particulate monitor and retrieved to the same ThinkAir cloud server. All data were then averaged for each hour of the measuring period. We were interested to see if regional, external PM2.5 levels might impact on internal PM2.5 data in the office. Therefore, internal hourly data were compared to a ThinkAir External continuous monitor, part of the ThinkAir Wales PM network situated in an urban background location 2.48 km (1.54 mi) from the office to determine any correlation between internal and external particulate levels (Figure 1).
Up to 3 members of staff occupied the office at desks each working day between the hours of 6.00am and 6.00pm. Maximum occupancy was generally between 9.00am and 5.00pm.
Internal vs. external PM2.5 levels
Hourly averaged PM2.5 data were analysed for a total of 7 working days during the study period (Figure 2). The temporal data reveal an interesting pattern where during the first four days of the study (Thursday 6th May to Sunday 9th May) internal PM2.5 generally mirrored levels, and changes in levels, of external measured PM2.5 (Pearson’s correlation coefficient = 0.6) as shown in Figure 3A. The Given the distance of just under 2.5km between office and urban background monitor, we propose that regional PM2.5 levels influenced the concentration of PM2.5 within the building.
During the remaining 5 study days, (Monday 10th May to Friday 14th May), internal PM2.5 levels increased significantly during a number of nights to levels exceeding 20 ug/m3 with a maximum peak concentration of 78 ug/m3. Following a peak, concentrations decreased during the early hours of the morning but sometimes rising again once staff arrived for work before decreasing again around midday (for two of the work days) as shown in the boxplots of Figure 4. There was no correlation observed between indoor PM2.5 concentrations and outdoor levels (Pearson’s correlation coefficient = 0.1) where outdoor levels remained below 20 ug/m3 (Figure 3B). These result suggest that night-time local PM2.5 sources contributed strongly to internal levels within the office and that high levels could be maintained during the day and thus increase fine particulate exposure.
Our case study reveals how temporal PM2.5 patterns in a small 3-person office environment can mirror external particulate levels and thus external PM2.5 can strongly influence the air pollution we breathe indoors. Our data also show the importance of urban background air pollution monitoring. Significantly, the availability of the ThinkAir PM2.5 monitoring network providing local data allows for workplaces to determine sources of internal air pollution and act to protect employees from the harmful effects of PM2.5.
4 WHO Regional Office for Europe, 2013. Review of Evidence on Health Aspects of Air Pollution – REVIHAAP Project Technical Report.