Source apportionment of carbonaceous submicron particulate matter in an urban area synthesizing the results of observation- and chemical transport model-based approaches

Particulate matter (PM) significantly impacts urban air quality and public health, making the quantification of its source contributions crucial for effective air quality management. In this work, we investigate the origins of organic aerosol (OA) and elemental carbon (EC) in an urban environment by synthesizing results from in situ observational analyses (receptor modeling) and chemical transport modeling. This study focused on the city of Barcelona, Spain, during a summer and a winter period in 2019, using measurement data from an aerosol chemical speciation monitor (ACSM), an Aethalometer, and analyses of filter samples along with source resolved predictions from the chemical transport model (CTM) PMCAMx. Results refer to PM1 (PM finer than 1 μm). Oxygenated OA (OOA) was the dominant source of OA during both periods with contributions ranging from 63 % of PM1 OA in winter to 80 % in summer. During summer, most of it originated from sources outside Barcelona such as wildfires, biogenic sources, as well as sources outside Europe. PMCAMx significantly underpredicted OOA during wintertime, suggesting that the model is lacking both processes that produce secondary OA (SOA) during periods of low photochemical activity and the corresponding emissions of organic pol lutants. Biomass burning OA (BBOA) emitted far away from the city and its conversion to SOA either due to nighttime or aqueous chemistry could explain part of the missing OOA. Hydrocarbon-like OA (HOA) ranged from 8 to 14 % of the OA in both periods, peaking during morning and evening rush hours. The primary OA (POA) emissions from transportation during winter may be underestimated in the emission inventory. Cooking OA (COA) was also a significant source (11 % of total PM1 OA) and it needs to be added to the current European emission inventories. Fresh BBOA was a small component of OA during summer and higher during winter. The PM1 EC levels were found to be dominated by local sources during both seasons. Among these sources, fossil fuel combustion was the most important contributor, accounting for approximately 74 % of the total EC. This highlights the strong influence of traffic and other fossil fuel-related activities on EC concentrations in Barcelona, regardless of season. This study demonstrates the value of integrating observational data (and receptor modelling) with chemical transport modeling to more accurately identify the sources of carbonaceous PM in urban environments. Such combined approaches are essential for developing effective mitigation strategies tailored to seasonal and local emission patterns, ultimately supporting improved air quality management.