First Quantification of Imidazoles in Ambient Aerosol Particles: Potential Photosensitizers, Brown Carbon Constituents, and Hazardous Components

Imidazoles are widely discussed in recent literature. They have been studied as a secondary product of the reaction of dicarbonyls with nitrogen containing compounds in a number of laboratory studies, potentially acting as photosensitizers triggering secondary organic aerosol growth and are forming constituents of light absorbing brown carbon. Despite the knowledge from laboratory studies, no quantitative information about imidazoles in ambient aerosol particles is available. Within the present study, five imidazoles (1-butylimidazole, 1-ethylimidazole, 2-ethylimidazole, imidazol-2-carboxaldehyde, and 4(5)-methylimidazole) were successfully identified and quantified for the first time in ambient aerosol samples from different environments in Europe and China. Their concentrations range between 0.2 and 14 ng/m³. 4(5)-Methylimidazole was found to be the most abundant imidazole. The occurrence of imidazoles seems to be favored at sites with strong biomass burning influence or connected to more polluted air masses. No connection was found between aerosol particle pH and imidazole concentration. Our work corroborates the laboratory studies by showing that imidazoles are present in ambient aerosol samples in measurable amounts. Moreover, it further motivates to explore the potential photosensitizing properties of small alkyl-substituted imidazoles

Additional file 1 of A novel in-situ method to determine the respiratory tract deposition of carbonaceous particles reveals dangers of public commuting in highly polluted megacity

Additional file 1. Experiment quality assurance and supplementary results. Table S1: List of related in situ respiratory tract deposition dose studies. Table S2: Summary of related in situ respiratory tract deposition studies using hydrophobic particles. Table S3: Mean DDR estimated using different assessment methods. Figure S1: Instrument laboratory intercomparison with reference system. Figure S2: Micro-aethalometer intercomparison in Leipzig, Germany. Figure S3: Micro-aethalometer intercomparison in Metro Manila, Philippines, using ambient street-site aerosol. Figure S4: Flow rate through dry and wet (after exposing to breath air) particulate filter. Figure S5: Descriptive statistics of measured parameters in TMEs between public transport and walking. Figure S6: Descriptive statistics of measured parameters separated between males and females. Figure S7: Deposition dose rate as a function of measured BC exposure concentrations