Delays to handover patients from ambulance crews to staff in Emergency Departments (ED) have become widespread. These patients receive care within ambulances whilst waiting in designated parking bays outside ED. During this time heating, cooling, lighting and medical equipment use is often required. Although the vehicle battery can provide electrical power for limited time without running the engine, climate control and additional power is provided by running the engine, also known as idling.
In 2022, a staff Union at East of England Ambulance Service NHS Trust (EEAST) received reports from paramedics who could smell exhaust fumes whilst in the back of ambulances parked outside ED. In 2023, this Union collected reports of staff feeling unwell after spending most of their shift outside ED, with symptoms including headaches, sore throat and tiredness.
The MAPA Pilot study tested methods of measuring air pollution in preparation for a larger study examining the air pollution outside hospitals. The pilot study was split into three workstreams, each using different methods but taking place at the same time.
Workstream 1 used static air quality sensors mounted on the walls in an ambulance bay at Cambridge University Hospital (CUH). The device measured carbon monoxide (CO), nitrogen dioxide (NO2) and particulate matter (PM10 and PM2.5) and recorded video of vehicle movements. The measurements obtained were compared to a reference sensor, outside of the ambulance bay. Records of ambulance activity were used to determine any association between the number of ambulances at the hospital and increased pollution levels. The sensors were left in place for 3 months.
Workstream 2 used smaller, handheld devices to measure air pollution inside ambulances. These devices were placed in the cab and saloon (patient compartment) of the ambulance by designated ambulance staff on each shift. The study collected data for one month, coinciding with the monitoring in Workstream 1.
Workstream 3 utilised physiological measurements of CO levels in ambulance staff waiting outside the hospital study site. Pulse CO-oximetry were used to measure physiological levels of CO in staff, as carboxyhaemoglobin (COHb). A member of research staff visited the site regularly and offered CO-oximetry to consenting healthcare staff waiting at hospital; each staff member completed a short health survey and recorded a CO measurement. Repeat measurements throughout the day demonstrated any effects of exposure to the pollution at hospital. This was conducted at the same time as Workstreams 1 and 2 to enable comparative data analysis.
Results from Workstreams 1 and 2 were compared for statistical associations between external air quality and internal air quality within an ambulance. The results from Workstream 3 were used to test whether measuring COHb is feasible in this population and generated a power calculation needed to demonstrate a link between external measurements of CO and physiological measurements of COHb.
Recommendations
MAPA Pilot has demonstrated a need for further investigation of air quality in ED ambulance bays and into the occupational exposure of ambulance staff to air pollution. Such future work is recommended to include:
Further investigation of the data set presented in this report, with focus on:
- the time dependent relationships between ambulance queue and concentrations of pollutants.
- understanding the peak concentrations of PM and CO observed inside ambulances.
Investigation of the effects of season and architecture on ambulance bay pollution, to understand air quality patterns over a 12-month period and in multiple hospitals.
- There are a variety of ambulance bay architectural features: open parking bays, low-level access ramps, full or partial canopies, courtyards or other enclosed spaces, underground access, etc.
- MAPA Pilot was conducted for 3 months during winter. Ambulance demand, hospital flow and the use of engines all vary considerably during the year.
Investigation of the potential impacts of air pollution on the health of ambulance staff, other NHS staff and patients.
Assembling a multi-professional stakeholder panel to develop solutions to eliminate, reduce, or mitigate the air pollution created outside ED.
- The results of MAPA show that air pollution is produced in the ED ambulance bay, and solutions to this will involve a whole system approach between key stakeholders.
In the short term, ambulance services may consider efforts to reduce to engine idling, using publicity campaigns, new engine technology, providing electric hook-ups and reducing queuing outside ED.
Workshop
On Tuesday 20 January 2026, CO Research Trust hosted the Measuring Air Pollution from Ambulances (MAPA) Pilot Workshop in partnership with the East of England Ambulance Service (EEAST). The workshop was convened in response to findings from the CORT funded MAPA Pilot research study and brought together stakeholders with an interest in air quality, healthcare sustainability, and ambulance operations. Click here to find out more.
