The impact of traffic on air quality in Ireland: insights from simultaneous kerbside and sub-urban monitoring of submicron aerosols

Abstract. To evaluate the impact of traffic on urban air quality, the chemical composition and sources of submicron aerosols (PM1) were simultaneously investigated at a kerbside site in Dublin city centre and a residential site in sub-urban Dublin (~ 5 km apart) from 4 September to 9 November in 2018. Through the detailed comparison of one-week non-heating period in early September and heating period in late October, 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 organic aerosol (OA) was the most important (46–63 % of PM1 or 1.0–8.7 μg m−3) at the residential site. The daily and weekly cycle of BC at the kerbside during non-heating 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, as well as the effects of wind speed and wind direction. As a result of vehicular emissions and the street canyon effect, the kerbside increment (from urban background) ratio of up to 25 : 1 was found for BC during the non-heating 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 18–27 % (0.9–1.2 μg m−3) 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 (~ 33 % or ~ 2.1 μg m−3), and oxygenated OA (31–37 % or 1.2–2.0 μg m−3). At the residential site, solid fuel burning contributed to approximately 50 % (2.7 μg m−3) of OA during the heating period, while oxygenated OA accounted for almost 65 % (0.5 μg m−3) of OA during the non-heating period. Based on simultaneous investigation of PM1 at different urban settings (i.e. residential vs kerbside), this study highlights temporal and spatial variability of sources within Dublin city centre and the need for additional aerosol characterisation 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.