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

Abstract

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/m(3). 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.

Technical note: Updated parameterization of the reactive uptake of glyoxal and methylglyoxal by atmospheric aerosols and cloud droplets

“…Both GLYX and MGLY are water-soluble, GLYX more so than MGLY (Betterton and Hoffmann, 1988;Zhou and Mopper, 1990). Taking into account salting effects, the effective Henry's law constant for GLYX in aerosol water can be several orders of magnitude higher than that of MGLY, depending on the aerosol ionic content (Kampf et al, 2013;Waxman et al, 2015). As α-dicarbonyl species, GLYX and MGLY exhibit similar aqueous-phase chemistry: they undergo reversible hydration and self-oligomerization (Ervens and Volkamer, 2010;Hastings et al, 2005;Sareen et al, 2010;Shapiro et al, 2009), they can be oxidized by aqueous-phase radicals to form organic acids or organosulfates (Carlton et al, 2007;Lim et al, 2013;Perri et al, 2010;Schaefer et al, 2012Schaefer et al, , 2015, and they can react with nitrogen-containing species to form brown carbon (De Haan et al, 2018;Lee et al, 2013;Maxut et al, 2015;Nozière et al, 2009;Powelson et al, 2014;Sareen et al, 2010;Schwier et al, 2010;Shapiro et al, 2009;Yu et al, 2011).…”

“…Carlton et al (2008) found that including in-cloud aqSOA production by GLYX in CMAQ improved agreement with aircraft observations. L. A. Curry et al: Updated parameterization of the reactive uptake of glyoxal and methylglyoxal Since these initial studies, more information has become available regarding the gas-particle partitioning of glyoxal and methylglyoxal (Ip et al, 2009;Kampf et al, 2013;Waxman et al, 2015;Yu et al, 2011) and their chemical processing in the aqueous phase, allowing a refinement of their representation in models.…”

Nitrogen-containing secondary organic aerosol formation by acrolein reaction with ammonia/ammonium

“…Li et al: Acrolein reaction with ammonia/ammonium Yu et al, 2011), or Mannich reaction (Nozière and Córdova, 2008;Wang et al, 2010) to form high molecularweight (high-MW) compounds in SOA. For example, compounds that possess two carbonyl groups (dicarbonyls), such as glyoxal and methylglyoxal, are important precursors of aqueous SOA (Galloway et al, 2014;Shapiro et al, 2009;Trainic et al, 2011;Volkamer et al, 2007;Yu et al, 2011;Zhao et al, 2006). A number of laboratory and field studies have highlighted the importance of carbonyl-to-imine reaction for the formation of light-absorbing nitrogen-containing organic compounds (NOCs) from dicarbonyls (De Haan et al, 2011;Hawkins et al, 2018;Lin et al, 2015).…”

Parts-per-billion Limits of Detection via Absorbance Spectroscopy: An Ultraviolet (254 nm) Absorbance Detector for Liquid Chromatography using a Light Emitting Diode (LED)

“…Aerosol brown carbon is of scientific interest due to its unknown origins, and its ability to affect climate by absorbing solar radiation in Earth's atmosphere [9][10][11][12][13][14][15][16][17][18][19][20]. While the exact chemical nature of aerosol phase BrC remains nebulous due to analytical limitations, several classes of chemical compounds have been implicated as potential candidates including nitroaromatics, oligomeric condensation products of lignin sub-units, oligomers of isoprene, imidizoles, charge-transfer compounds, and reaction products of carbonyls with amines [21][22][23][24][25][26][27][28][29]. To complicate matters further, airborne particles are consistently exposed to a mixture of reactive gases such as ozone, oxides of nitrogen, peroxides, and sunlight that can functionalize or fragment molecules further [30][31][32][33][34][35].…”