Measurements and Modelling of Glyoxal in the Tropical Marine Boundary Layer

Abstract:

Glyoxal (CHOCHO) is a reactive volatile organic compound (VOC) produced during the atmospheric oxidation of both anthropogenic VOCs, such as acetylene and benzene, and biogenic VOCs, such as isoprene and monoterpenes. The photo-oxidation of glyoxal leads to the rapid production of peroxy radicals and condensable products, which are expected to result in formation of secondary organic aerosol (SOA).

We report new measurements of glyoxal in the tropical marine boundary layer, which were made using laser-induced phosphorescence (LIP) spectroscopy at the Cape Verde Atmospheric Observatory in June and August-September 2014 during the Ocean Reactive Carbon: Chemistry-Climate impacts (ORC3) campaign. The measurement site is marked by an absence of coastal features such as extensive shallows or large seaweed beds, and receives clean, well-processed marine air more than 95 % of the time, with minimal influence from local effects.

Maximum glyoxal mixing ratios of ~15 ppt were observed during the ORC3 campaigns, with typical daytime maxima of ~ 5-6 ppt during June and ~ 6-8 ppt during August-September, and nighttime minima of ~ 4 ppt and ~4-5 ptt during June and August-September, respectively.

This presentation will summarise these new measurements of glyoxal, in conjunction with box model simulations using the Master Chemical Mechanism (MCM). Simulations are constrained to observations of glyoxal precursors, and are used to investigate the sources and sinks of glyoxal in the tropical marine boundary layer.

Model calculations significantly underestimate the observed abundances of glyoxal, indicating the need for additional sources in the model. A number of possible scenarios will be discussed to explain the discrepancy between the measurements and the model.