Seasonal variability and source-related molecular marker profiling of carboxylic acids and phenols in urban PM10

Carbonaceous particulate matter plays a central role in urban air quality, yet integrated molecular-level characterization of phenolic compounds and carboxylic acids within the same actively sampled PM 10 matrix remains scarce for temperate European cities. This study investigates the seasonal variability and source relationships of 22 carboxylic acids, comprising 14 dicarboxylic acids and 8 fatty acids, and 53 phenolic compounds across five structural families (alkylphenols, nitrophenols, chlorophenols, bromophenols, and aminophenols) in weekly PM 10 samples collected at an urban background site in Strasbourg, France, over a 36-week campaign. Of the targeted compounds, 19 carboxylic acids and 20 phenols were detected and quantified. Total DCA concentrations ranged from 0.02 to 55.4 ng m -3 , with phthalic acid as the dominant species (median 3.3 ng m -3 ), reflecting strong anthropogenic and secondary photochemical inputs. FAs accounted for approximately 70% of the total measured organic acid mass and were dominated by hexadecenoic acid (C 16 ), nonanoic (C 9 ), and decanoic (C 10 ) acids, the latter two exhibiting severely episodic distributions driven by intermittent cooking-emission events. Within the phenomenon, chlorophenols constituted the largest annual contribution (44.9%), followed by alkylphenols (22%) and nitrophenols (21%), pointing to the importance of secondary halogenation chemistry alongside combustion-related primary and nitration pathways. Seasonal analysis revealed a clear compositional restructuring: DCAs shifted from dominance by phthalic and succinic acids in winter to malonic acid prevalence in summer, consistent with enhanced photochemical oxidation, phenolic profiles transitioned from co-dominance of nitrophenol and dichlorophenol in winter toward progressively more chlorinated and brominated species in summer and autumn. Spearman rank correlation analysis confirmed strong intra-family associations within both the mid-chain DCA cluster (C 5 -C 8 ; ρ = 0.84-0.97) and the chlorophenol subgroup (2,4-DCP vs. 2,6-DCP; ρ = 0.93), while cross-family correlations between organic acids and phenols were uniformly weak (|ρ| < 0.35), indicating largely independent source influences and formation mechanisms. Comparison with previously published fogwater, rainwater, and passive air monitoring data from the same region highlights matrix-dependent partitioning, particularly the pronounced aqueous-phase enrichment of nitrophenols relative to the particulate fraction. Together, these findings provide the first integrated seasonal characterization of both compound families in actively sampled urban PM 10 for a representative temperate European environment, establishing a molecular baseline for future receptor modeling and long-term trend assessment.