Effects of anthropogenic emissions on the molecular composition of urban organic aerosols: An ultrahigh resolution mass spectrometry study

•Ultrahigh resolution mass spectrometry was applied for the analysis of urban aerosol.•Up to 850 elemental formulas were identified in negative ionisation mode.•The samples contained a large number of oxidized aromatic and nitroaromatic species.•The identified biogenic OA species are later-generation nitrogen- and sulphur-containing molecules.•The results suggest that the site is affected by anthropogenic and natural sources of aerosol.

Identification of the organic composition of atmospheric aerosols is necessary to develop effective air pollution mitigation strategies. However, the majority of the organic aerosol mass is poorly characterized and its detailed analysis is a major analytical challenge. In this study, we applied state-of-the-art direct infusion nano-electrospray (nanoESI) ultrahigh resolution mass spectrometry (UHRMS) and liquid chromatography ESI Quadrupole Time-of-Flight (Q-TOF) MS for the analysis of the organic fraction of fine particulate matter (PM2.5) collected at an urban location in Cork, Ireland. Comprehensive mass spectral data evaluation methods (e.g., Kendrick Mass Defect and Van Krevelen) were used to identify compound classes and mass distributions of the detected species. Up to 850 elemental formulae were identified in negative mode nanoESI-UHR-MS. Nitrogen and/or sulphur containing organic species contributed up to 40% of the total identified formulae and exhibited strong diurnal variations suggesting the importance of night-time NO3 chemistry at the site. The presence of a large number of oxidised aromatic and nitroaromatic compounds in the samples indicated a strong anthropogenic influence, i.e., from traffic emissions and domestic solid fuel (DSF) burning. Most of the identified biogenic secondary organic aerosol (SOA) compounds are later-generation nitrogen- and sulphur-containing products, indicating that SOA composition is strongly affected by anthropogenic species such as NOx and SO2. Unsaturated and saturated C12-C20 fatty acids were found to be the most abundant homologs with a composition reflecting a primary marine origin. The results of this work demonstrate that the studied site is a very complex environment affected by a variety of anthropogenic activities and natural sources.