Carbonaceous aerosols in five European cities: Insights into primary emissions and secondary particle formation

Carbonaceous material is an important component of atmospheric aerosol particles, which plays a significant role in air quality and climate, and also has potentially negative impacts on human health. There is a lack of data reported in the literature regarding the carbonaceous fraction of aerosol in the North-West European ‘air pollution hotspot’ and this work reports a comprehensive one-year intensive measurement campaign, where organic carbon (OC) and elemental carbon (EC) fractions of PM10 (particulate matter of diameter ≤ 10 μm) were measured. Owing to the importance of carbonaceous aerosols in understanding particulate pollution sources, ~2000 PM10 samples were simultaneously collected across North-West Europe at four urban background sites located in Amsterdam (AD), Antwerp (AP), Leicester (LE) and Lille (LL), and one industrial site at Wijk aan Zee (WZ). PM10 samples were chemically analysed by OC-EC analyser for carbonaceous species (OC, and EC) and trends were identified. OC accounted for 12.8%, 13.9%, 15.3%, 15.1% and 9.8%, and EC accounted for 2.4%, 4.9%, 4.4%, 4.0%, and 2.4% of total PM10 mass for AD, AP, LE, LL and WZ, respectively. Secondary organic carbon (SOC) contributions were higher in warmer months compared to colder months, and SOC concentration levels were similar at all five locations, with SOC contributing more than primary organic aerosol (POC) in each city. The lower effective carbon ratio (ECR) values (≤0.3) at all five sites in October, November, and February can be attributed to higher combined POC and EC concentrations and lesser contributions from SOC, meaning that SOC with a greater relative formation has a greater tendency to disperse solar radiation. Higher ECR values in April, May, and July, on the other hand, indicate that more absorbing types of carbonaceous aerosols are also present. More than 90% of the air-mass trajectories were from the north and northeast. This paper details atmospheric processes and sources influencing the seasonal variability of the carbonaceous components of PM10.