Aerosols present in the upper troposphere and lower stratosphere (UT/LS) are composed mainly of sulfuric acid (40-80 wt. %) and water; therefore, climate models treat them as highly scattering to sunlight, resulting in an overall cooling effect. However, airborne measurements have shown that many UT/LS aerosols also contain a significant fraction of organic compounds, which could alter their climate-forcing properties. In particular, we have previously shown that reactions of propanal in sulfuric acid produce highly colored surface films which are a complex mixture of aldol condensation products, acetals, and propanal itself. Such films could significantly alter the optical and/or cloud-forming properties of UT/LS aerosols. However, atmospheric concentrations of propanal alone are too low to produce a significant amount of aerosol surface film. Instead, products of cross-reactions between multiple aldehydes would be required. In order to determine whether these cross-reactions are likely to occur in UT/LS aerosols, mixtures of propanal with other common aerosol organic species (glyoxal and methylglyoxal) in sulfuric acid were prepared. Surface films formed on these multiple-aldehyde mixtures, and were chemically analyzed via attenuated total reflectance Fourier transform infrared (ATR-FTIR) and <sup>1</sup>H nuclear magnetic resonance (NMR) spectroscopies. The results demonstrate the presence of products of cross-reactions between propanal and glyoxal or methylglyoxal. Therefore, these reactions have the potential to produce significant organic aerosol mass, which could partition into surface films and impact optical, chemical, and/or cloud-forming properties of aerosols.

Evidence for products of cross-reactions in organic films formed on sulfuric acid solutions at upper troposphere/lower stratosphere aerosol acidities

255th National Meeting (2018)

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