Air quality at Connolly Station is not at its worst level during peak commuting time, but rather pollution from trains builds up whendiesel multiple units are left idling at lower-frequency times, researchers from Trinity College Dublin have found.All fixed monitored locations across the station exceeded the EUs annual limit for nitrogen dioxide (NO2) concentration, and PM2.5, fine particulate matter less than 2.5 micrometres in diameter, exceeded the World Health Organisations 24-h limit during 90% of the monitoring period.Peak pollution occurs when there are fewer train movements, and diesel multiple unit (DMU) trains serving the Northern Line and Western Lines are left idling for longer periods. This includes the early mornings before 7am, around midday when there is a notable gap in the timetable, and after 10pm at night.Pollution is also generally worse on weekends than during the week, the researchers wrote: The average concentrations on weekends were 1.2 to 1.25 times higher than on weekdays, due to lower train frequency and consequently longer idling times.The researchers paper has just been published in Environmental Pollution, a peer-reviewed academic journal covering the health effects of environmental pollution.In the paper, researchers outline how poor air quality is one of the biggest risks to public health globally and is known to worsen pre-existing health conditions such as cardiovascular and respiratory diseases, but there is a lack of research on pollution at transport hubs such as ports, bus terminals, and train stations, which can be hotspots for pollution.Average NO2concentrations varied significantly between the enclosed and outdoor platforms. On the enclosed platforms, concentrations during the measurement campaign ranged from 83.0 to 162.7g/m3, with particularly high levels observed across the full length of the enclosed Platform 4, the TCD researchers said.In contrast, NO2concentrations on the open platforms ranged from 40.5 to 71.5g/m3, with elevated levels observed at the open end of Platform 3. Concentrations in the Concourse area and station entrance ranged from 63 to 68g/m3and 56 to 59g/m3, respectively. All fixed monitored locations across the station exceeded the EU annual NO2limit of 40g/m3, they said.Researchers said that NO2 concentrations were higher during periods of low train traffic, where trains experienced longer idling time before departure. They said that concentrations of PM2.5 were higher when DMU trains were on platforms compared to pushpull trains, the type of trains mainly used by the Belfast to Dublin train service.The 24-h average PM2.5 measured using continuous fixed monitoring ranged between 3.18 and 32.56 g/m3. Higher PM2.5 averages were observed on enclosed Platforms 3 and 4, which predominantly host DMU trains, exceeding the WHO 24-h limit during 90% of the monitoring period, the researchers said. Based on operational analysis, researchers recommend that Irish Rail should shut down DMU engines when the next train service is more than 30 minutes away, and only restart them 15 minutes before departure. During the idling time, they also suggest maintaining idle speeds below 600 RPM.They estimate that such action could save over 7,000 L of diesel per month, reduce fuel consumption by 4045%, and lower NOx and PM emissions by around 54%, offering actionable strategies to improve station air quality.The TCD researchers said that while wind speed was not found to be a key influencing factor. However, when wind speeds exceeded 0.2 m/s, a decrease in NO2 levels was observed, which suggests that enhancing ventilation and increasing airflow within the station could also be a strategy to reduce NO2 concentrations, in addition to managing train idling time.The paper points out that several studies have recommended mitigation strategies such as improved ventilation, reduced idling time, the use of diesel particulate filters with catalytic regeneration, scheduling diesel trains in open areas of the station, installing platform screen doors to minimise public exposure, and electrifying trains as a long-term solution. Electrifying most suburban train services which use the station is planned as part of Dart+, but this will be done on a phased basis and will take years to complete. The research, published in open access format in the May 15th edition of the journal Environmental Pollution, was conducted by Shanmuga Priyan, Muireann Kearney, Neha Jacob, Yuxuan Guo, Madhavan Vasudevan, Aonghus McNabola, Brian Broderick, Brian Caulfield, Margaret OMahony, and John Gallagher.