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, in partnership with EMSOL, the University of Suffolk, and Anglia Ruskin University, the study provides 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 Praxis MCERTS-certified air quality monitoring at Addenbrooke’s Hospital’s ED ambulance bay and compared readings against a secondary background ‘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 background 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. Addenbrook’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

There is currently no specific regulatory requirement to monitor air quality in ambulance bays. Until now, trusts haven’t had quantified data to assess this environment. The MAPA Pilot Study’s findings of DEFRA threshold breaches and WHO guideline exceedances, combined with staff reporting symptoms, provide that baseline evidence.

This study represents important UK data on ambulance bay air quality, not the final word. The authors recommend further research across multiple hospitals with different bay designs, year-round monitoring to understand seasonal variations, and investigation of health impacts on staff and patients.

For trusts experiencing persistent ambulance handover delays, this 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.

Many thanks to Callum Brown and Theresa Foster from the East of England Ambulance Service Trust for their support, and to the CO Research Trust for enabling the project to happen (reword but worth saying a thank you)

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