Cambridge University Hospital study shows pollution exceeding WHO guidelines – what NHS trusts need to know

In December 2022, 1,814 ambulances waited more than 10 hours outside English Emergency Departments. While the NHS has focused on reducing these handover delays, virtually no data existed on a related consequence: the air quality ambulance staff and patients are exposed to while queuing outside hospitals.

The Measuring Air Pollution from Ambulances (MAPA) Pilot Study, conducted between November 2024 and March 2025, has changed that. Funded by the Carbon Monoxide Research Trust and led by researchers from East of England Ambulance Service NHS Trust, the University of Suffolk, and Anglia Ruskin University, the study provides the first reliable UK data on pollution exposure in and around ambulance bays.

The findings raise important questions for NHS trusts about occupational health, patient safety, and environmental monitoring obligations.

Researchers installed EMSOL’s Parxis MCERTS-certified air quality monitoring at Cambridge University Hospital’s ED ambulance bay and compared readings against a reference sensor on the access road leading to the bay.

The monitors operated continuously from 9th December 2024 to 1st March 2025, capturing 95 days of winter data. The measurements covered PM2.5 (fine particulate matter with diameter of 2.5 microns or less), PM10 (coarse particulate matter, 10+ microns), Nitrogen Dioxide (NO2), and Carbon Monoxide (CO).

The Key Findings

Pollution Levels Exceeded WHO Guidelines

Particulate matter (PM2.5) concentrations in the ambulance bay averaged 19.56 µg/m³, breaching WHO’s daily guideline of 15 µg/m³ on 22 days during the study period. The mean concentration exceeded WHO’s annual guideline of 5 µg/m³ by nearly four times, though it remained just below the UK’s legally binding annual limit of 20 µg/m³.

For PM10, the ambulance bay recorded a mean of 33.79 µg/m³. DEFRA’s daily threshold of 50 µg/m³ was breached on 15 days (16% of the study period), while WHO’s stricter daily guideline of 45 µg/m³ was exceeded on 22 days (23% of the study period).

DEFRA legislation allows up to 35 days per year where the daily PM10 threshold can be exceeded. However, in just three months of winter monitoring, the ambulance bay accumulated 15 breach days, suggesting potential annual exceedance of legal limits if this pattern continues year-round.

Nitrogen dioxide (NO2) concentrations were consistently elevated, averaging 59.43 µg/m³ in the ambulance bay. This exceeded WHO’s daily guideline of 25 µg/m³ on every single day data was available (90 days). The mean also exceeded DEFRA’s annual limit of 40 µg/m³ and WHO’s annual guideline of 10 µg/m³ by nearly four times.

Carbon monoxide levels remained below both DEFRA and WHO thresholds throughout the study. However, approximately one in five ambulance bay staff reported symptoms that began while working in the ambulance bay, most commonly headaches, fatigue and back pain.

The Ambulance Bay Created a Pollution Hotspot

Comparison between the ambulance bay sensor and the reference sensor on the access road revealed a clear pattern. PM2.5 readings in the ambulance bay were higher 92% of the time, while PM10 readings were elevated 85% of the time. NO2 was higher 68% of the time, and CO showed elevated readings 90% of the time. These differences were statistically significant across all pollutants measured.

This pattern suggests that architectural design plays a significant role in pollution concentration. Cambridge’s courtyard layout with partial canopy appears to trap pollution, creating an exposure hotspot compared to the nearby access road. Different ambulance bay designs at other hospitals may show different patterns.

Queue Length Wasn’t Directly Correlated with Pollution

Perhaps surprisingly, researchers found no direct correlation between the number of ambulances queuing and pollution levels. The study recorded ambulance queue data every 30 minutes, with queue lengths ranging from zero to 26 vehicles. Despite this variation, statistical analysis revealed no clear relationship between queue size and pollutant concentrations.

This finding suggests pollution patterns are influenced by multiple factors including architectural design, wind patterns, time of day, and specific vehicle activities, not simply the number of vehicles present. Understanding these complex interactions requires continuous monitoring rather than assumptions based on queue length alone.

What This Means for NHS Trusts

Regulatory and Legal Context

The legal framework here has several layers. DEFRA sets legally binding limits for outdoor air quality in the UK, and employers have duties under the Health and Safety at Work Act 1974 and the Management of Health and Safety at Work Regulations 1999 to assess and control workplace risks. HSE’s COSHH regulations apply to exposure to hazardous substances, which can include vehicle emissions in certain contexts.

However, there is currently no specific regulatory requirement to monitor air quality in ambulance bays or loading bays. The study’s findings of DEFRA threshold breaches and WHO guideline exceedances, combined with staff reporting symptoms, create a potential occupational health concern that trusts may need to consider under their general duty of care obligations. The absence of specific guidance doesn’t eliminate the responsibility to assess and manage workplace health risks.

Who Owns This Issue?

This sits at the intersection of several responsibilities within NHS trusts.

• Health and Safety or Occupational Health teams will be concerned with staff exposure to pollutants and symptom reporting.
• Estates and Facilities teams manage physical infrastructure, ventilation, and bay design.
• Risk Management considers potential liability and duty of care obligations.
• Emergency Department and Site Operations teams handle ambulance bay protocols and vehicle management.

The study examined one hospital with a specific architectural layout during winter months. However, ambulance handover delays are a systemic NHS issue, and the pollution sources (idling diesel engines) are universal across the country.

What Happens Next?

The MAPA Pilot Study represents the first UK data on this issue, not the final word. The authors recommend further research across multiple hospitals with different ambulance bay designs, year-round monitoring to understand seasonal variations, investigation of health impacts on ambulance staff, ED staff and patients, and development and testing of practical interventions.

NHS trusts don’t need to solve this problem immediately or independently. However, the study provides evidence that air quality in ambulance bays is measurable, potentially significant, and worthy of consideration in your trust’s risk management and occupational health frameworks.

For trusts experiencing persistent ambulance handover delays, this study adds an environmental health dimension to a well-known operational challenge. Understanding the scale of the issue at your specific site is the logical first step.

For more information:

• Complete MAPA Pilot Study report: Available from East of England Ambulance Service NHS Trust Research Support Services
• EMSOL MCERTS-certified monitoring solutions to conduct a study at your trust – contact sales@emsol.io