AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Organic-nitrogen Compound Formation via Aqueous Photo-oxidative Processing of Glyoxal in the Presence of Different Inorganic Salts
ALEX K. Y. LEE, John Liggio, Shao-Meng Li, Jonathan Abbatt, University of Toronto
Abstract Number: 247 Working Group: Aerosol Chemistry
Abstract Formation of particle-phase organic-nitrogen compounds has been proposed via aqueous chemistry of glyoxal and (NH$_(4))$_(2)SO$_(4) in dark and illuminated conditions. In the atmosphere, glyoxal likely co-exists with many other inorganic components in aqueous droplets but their molecular interactions are still not well understood. The primary goal of this study is to investigate the formation of organic-nitrogen species through aqueous photo-oxidative processing of glyoxal in the presence of different inorganic salts (e.g., (NH$_(4))$_(2)SO$_(4), NH$_(4)HSO$_(4), NH$_(4)NO$_(3), Na$_(2)SO$_(4) and NaNO$_(3)). Aqueous-phase OH oxidation of glyoxal was performed using a photochemical reactor that allows simultaneous atomization of the reacting solution. The elemental composition of aqueous droplets were analyzed by the Aerodyne High Resolution Aerosol Mass Spectrometer (HR-AMS).
According to our preliminary results, organic-nitrogen fragments at m/z 68 (C$_(3)H$_(4)N$_(2)$^(+)) and 69 (C$_(3)H$_(3)NO$^(+)) immediately formed when glyoxal was mixed with (NH$_(4))$_(2)SO$_(4), NH$_(4)HSO$_(4) or NH$_(4)NO$_(3) in dark conditions. Note that these organic-nitrogen fragments were not observed in pure glyoxal or pure inorganic solutions. The above observations are possibly due to the formation of 1H-imidazole-2-carboxaldehyde in the mixed solution. By contrast, mixing of glyoxal with Na&_(2)SO&_(4) or NaNO$_(3) did not produce these fragments, further suggesting that the NH$_(4)$^(+) is an essential component to produce organic-nitrogen compounds in these systems. From the photo-oxidation experiments of glyoxal, we observed that the organic fragment C$_(3)H$_(4)N$_(2)$^(+) at m/z 68 increased in abundance with OH exposure in the case of (NH$_(4))$_(2)SO$_(4), NH$_(4)HSO$_(4) and NH$_(4)NO$_(3). In particular, aqueous-phase OH oxidation of glyoxal-NH$_(4)NO$_(3) solutions can produce much higher m/z 68 signal than all other solutions. Because NaNO$_(3) and (NH$_(4))$_(2)SO$_(4) did not lead to the same effect as NH$_(4)NO$_(3) during photo-oxidation, we believe that the organic-nitrogen peaks are predominantly arising through ammonium chemistry but photo-chemistry involving nitrate may play a role in enhancing this formation processes. Furthermore, our results suggest that the presence of Na$^(+) may suppress the organic-nitrogen species formation.