Identification and characterization of aging products in the glyoxal/ammonium sulfate system – implications for light-absorbing material in atmospheric aerosols

C J Kampf,T Hoffmann,R Jakob

doi:10.5194/acp-12-6323-2012

C J Kampf, T Hoffmann + Show 1 more

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https://doi.org/10.5194/acp-12-6323-2012

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Abstract

Abstract. In this study we report the identification of bicyclic imidazoles in aqueous aerosol mimics using HPLC-ESI-MS/MS. 2,2'-Biimidazole was identified to be a major contributor to the 280 nm absorbance band observed in mixtures of glyoxal and ammonium sulfate, despite the fact that its production rate is two orders of magnitude lower than the previously reported production rates of imidazole or imidazole-2-carboxaldehyde. The molar absorptivity of 2,2'-biimidazole was determined to be (36 690 ± 998) M−1 cm−1. This demonstrates the necessity of molecular product identification at trace levels to enable a better understanding of relevant absorbing species. Additionally, the formation of lower polarity products including formamides of imidazoles is proposed. The role of imidazoles and other light-absorbing species in the formation of SOA and optical properties of SOA is discussed and potentially interesting fields for future investigations are outlined.

Highlights

Atmospheric aerosols impact global and regional climate, air quality and human health (Seinfeld and Pandis, 2006)
The reaction of glyoxal with ammonia, which is present in ammonium sulfate solutions in concentrations dependent on the pH value of the solution, yields a variety of different imidazoles
We believe BI is a major contributor to lightabsorbing material formed in the Gly/ammonium sulfate (AS) system it is only produced in small amounts as will be discussed in the following Sect. 3.2

Summary

Introduction

Atmospheric aerosols impact global and regional climate, air quality and human health (Seinfeld and Pandis, 2006). Over the past years the perception that secondary organic aerosols (SOA) are formed only by gas to particle conversion of low volatility products from atmospheric oxidation processes of volatile organic compounds (VOCs) (Pankow 1994; Odum et al, 1996) has changed and involves heterogeneous chemistry and particle phase chemistry of more volatile oxidation products (Hallquist et al, 2009; Lim et al, 2010; Ervens et al, 2011) Prominent examples of such compounds are the two simplest and most abundant α-dicarbonyl compounds glyoxal (Gly) and methylglyoxal (Mgly), which remain at least partly in the particle phase through a number of possible reaction pathways in the condensed phase. Oxidation of Gly and Mgly in the particle phase by OH radicals resulting in the formation of lower volatility carboxylic acids (e.g. oxalic acid or pyruvic acid) (Carlton et al, 2007; Tan et al, 2009, 2010; Lim et al, 2010; Altieri et al, 2008) are discussed as sources of SOA from small α-dicarbonyl compounds

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