Using air quality sensor networks to compare variations of PM2.5 in a small town and a city in Ireland.

High density air quality sensor (AQS) networks offer a unique opportunity to better understand the local variations and temporal patterns of air pollutant levels in a city. With the coordination of reference instrumentation and meteorological data, they are even more useful. This work compares two sensor networks that are the first or their kind in Ireland. The first is in Cork City (population ~ 220,000) in the south of Ireland, which currently has five regulatory monitoring stations, three of which monitor PM_2.5. The second location is Edenderry which is a rural town (population ~ 8,000) in the Irish midlands served by one regulatory monitoring site. The Cork City AQS network is comprised solely of PurpleAir devices, while the Edenderry network combines both PurpleAir and Clarity Movement Co. devices. The networks provide increased spatial and temporal data in relation to PM_2.5.

Both locations experience seasonally elevated levels of PM_2.5 due to higher instances of domestic solid fuel burning during the winter months. However, Edenderry generally experiences significantly higher levels, despite its much smaller size. During the winter heating period of 2020-2021 (01/10/20 - 31/0321), there were 23 instances where the PM_2.5 24-hour mean at a regulatory monitoring site in Cork exceeded the WHO Global Air Quality Guidelines of 15 µg m^-3, while there were 83 instances in Edenderry over the same period.

A correction model was applied to the AQS data collected in both networks to align the values with respective local reference data. Multiple linear regression (MLR) models were used to calibrate the networks using data from periods of colocation of the reference instrument with air quality sensors. By combining these robustly calibrated and co-ordinated networks with local meteorological information, the data was used to investigate the local spatial and temporal variations in PM_2.5 for the period 01/02/2022 to 29/07/2022. The typical daily cycle of PM pollution in Ireland was observed in both locations, with a dominant afternoon/evening peak during the colder months due to solid fuel burning for home heating. Significant PM_2.5 variations between sensor locations in each network were found. The results showed that a small town in Ireland can experience PM_2.5 pollution levels that are as substantially higher than more populated urban areas.

This work was supported by the EU LIFE Programme through the project LIFE Emerald - LIFE19 GIE/IE/001101 and the Cork City AQS network is supported by Cork City Council.