The impact of traffic on air quality in Ireland: insights from the simultaneous kerbside and suburban monitoring of submicron aerosols

To evaluate the impact of traffic on urban air quality, the chemical composition of submicron aerosols (PM1) and sources of organic aerosol (OA) were simultaneously investigated at a kerbside site in the Dublin city center and a residential site in suburban Dublin (∼ 5 km apart) from 4 September to 9 November in 2018. Through the detailed comparison of a 1-week nonheating period from 10 to 17 September and a 1-week heating period from 27 October to 4 November, black carbon (BC) was found to be the most dominant component (38 %–55 % or 5.6–7.1 µg m−3) of PM1 at the kerbside, while OA was the most important (46 %–64 % of PM1 or 1.0–8.1 µg m−3) at the residential site. The daily and weekly cycle of BC at the kerbside during the nonheating period pointed to the major source of vehicular emissions, consistent with that for nitrogen oxides (NOx). However, traffic emissions were found to have a minor impact on air quality at the residential site, due to its distance from traffic sources and the effects of wind speed and wind direction. As a result of vehicular emissions and the street canyon effect, the kerbside increment (from the urban background) ratio of up to 25 : 1 was found for BC during the nonheating period but reduced to 10 : 1 during the heating period due to the additional sources of solid fuel burning impacting the air quality at both sites simultaneously. OA source analysis shows only 16 %–28 % (0.9–1.0 µg m−3; upper limit for traffic due to the additional heating source of hydrocarbon-like OA – HOA) of OA at the kerbside associated with vehicular emissions, with higher contributions from cooking (18 %–36 % or 1.2 µg m−3), solid fuel burning (38 % or 2.4 µg m−3; resolved only during the heating period), and oxygenated OA (29 %–37 % or 1.2–1.9 µg m−3). At the residential site, solid fuel burning contributed to 60 % (4.9 µg m−3) of OA during the heating period, while oxygenated OA (OOA) accounted for almost 65 % (0.6 µg m−3) of OA during the nonheating period. Based on simultaneous investigations of PM1 at different urban settings (i.e., residential versus kerbside), this study highlights the temporal and spatial variability of sources within the Dublin city center and the need for additional aerosol characterization studies to improve targeted mitigation solutions for greater impact on urban air quality. Moreover, traffic and residential heating may hold different implications for health and climate, as indicated by the significant increment of BC at the kerbside and the large geographic impact of OA from residential heating at both the kerbside and residential sites.