Cooperative Institute for Research in Environmental Sciences

A winning proposal for the Innovative Research Program, 2009:

Secondary organic aerosol formation from glyoxal: Linking laboratory, field and model studies

Investigators: Barbara Ervens (CIRES, and NOAA/ESRL/CSD) Rainer Volkamer (CU Dept. of Biochemistry and Chemistry, and CIRES)

Objective
We propose to develop a module that represents the aqueous phase chemistry of glyoxal to form low-volatility oligomers, sulfate and/or ammonium adducts based on recent laboratory data. We will implement this module into an existing parcel model to evaluate for the first time for atmospheric conditions the relative importance of these formation routes for secondary organic aerosol (SOA) in haze particles (‘SOAhaze’). The model will be applied to a case study in Mexico City (9 April 2003) in order to test the ability to reproduce field observations of SOA formation, assess the relative importance of different pathways in haze particles and cloud droplets. A computationally efficient (reduced) approach will be developed for modeling studies at a larger (regional/global) scale.

Background and importance
Uncertainties in estimating the effects of aerosols on the global radiative forcing arise due to the complexity of aerosol properties and the diversity in their source and sink processes. A significant fraction of fine aerosol mass is organic, and most organic aerosol forms in the atmosphere as a result of chemical transformations of precursor gases (secondary organic aerosol, SOA). Current models describe SOA formation by condensation of low-volatility oxidation products from precursors (≥ C7) into an organic aerosol phase, ignore chemistry in the aqueous phase, and underestimate SOA mass by factors of 5-100 [1] (Fig. 1a). For the case study in Mexico City (April 9, 2003), we demonstrated for the first time that SOA formation from volatile glyoxal (C2) is an atmospherically relevant SOA source also in the absence of clouds, and helps bring measured and predicted SOA in better agreement [2] (Fig.1b). In lack of a detailed chemical model that represents glyoxal chemistry in aerosol water, previous interpretation of our field data could not distinguish which reaction pathway is most responsible for the SOA mass inferred to form from glyoxal.
Numerous recent laboratory studies now provide means to parameterize the formation of oligomers and sulfate and/or ammonium adducts (e.g.,[3, 4]); such species have indeed been identified in the SOA fraction of ambient particles. The small amount of water on ambient haze particles (~10-10-10-7 gH2O/gair) provides a unique medium for chemical reactions that are different from those in dilute cloud droplets [3, 5, 6] (much higher liquid water content: ~10-4 gH2O/gair). The high organic and inorganic solute concentrations in haze particles accelerate reaction rates, and appear to lead to different products. To date, no systematic attempts have been made to understand the relative importance of these various possible reaction pathways of glyoxal to form SOA in haze particles, and clouds.

What makes it innovative
The proposed study represents a new link between recent laboratory studies and observations of the atmosphere towards a quantification of SOA formation in haze particles and clouds by creating a modeling tool on a process basis. The long experience of the proposers in the development of multiphase models (Ervens) and in laboratory and field measurements of glyoxal (Volkamer) will allow a reliable implementation of all available data into an existing chemical/microphysical parcel model.

Research plan The development and application of the model will be carried out by a PostDoc who will work closely with both PIs.

1. Including all glyoxal reaction parameters in the multiphase parcel model that are appropriate for the selected case study (1, Fig.2)
2. Creating trajectories to drive the parcel model using observed meteorological data. If data (e.g., reactant concentrations) are not available, find suitable basis for estimates (2, Fig.2)
3. Identification of the most significant processes for SOAhaze formation from glyoxal. Sensitivity tests will be performed to assess the importance of selected parameters (relative humidity, glyoxal/ oxidant concentrations, aerosol mass/size, …) to newly formed SOA mass (3 and 4, Fig.2)
4. Parameterization of the explicit reaction scheme to reduce complexity and increase computational efficiency for inclusion in a global model (5, Fig. 2)
5. Publication of the case study results, including recommendation for further laboratory and field studies in order to quantify SOAhaze formation.

Expected outcome and impact
This work will be the first assessment of the drivers for SOA formation from glyoxal in haze. The results will help guide further laboratory studies by revealing weakness in the current process description and understanding (3 in Figure 2). In addition, the model will show under what conditions significant SOAhaze production can be expected and help guide future field experiments (4, Fig. 2). A new (parameterized) ‘SOAhaze module’ will be developed and made available to the modeling community to be implemented in larger scale models that describe aerosol formation on regional or global scales (5, Fig. 2). Thus, the proposed project will lead to a reduction in the gap between observed and modeled SOA mass by providing better model tools, and will contribute to a better representation of aerosol formation and properties in the climate system.

References
1 Volkamer, R., J.L. Jimenez, F. SanMartini, K. Dzepina, Q. Zhang, D. Salcedo, L.T. Molina, D.R. Worsnop, and M.J. Molina, Secondary organic aerosol formation from anthropogenic air pollution: Rapid and higher than expected. Geophys. Res. Lett., 2006. 33(L17811): doi: 10.1029/2006GL026899.
2 Volkamer, R., F. SanMartini, L.T. Molina, D. Salcedo, J. Jimenez, and M.J. Molina, A missing sink for gas-phase glyoxal in Mexiko City: Formation of secondary organic aerosol. Geophys. Res. Lett., 2007. 34(L19807): doi: 10.1029/2007GL030752.
3 Volkamer, R., P.J. Ziemann, and M.J. Molina, Secondary organic aerosol formation from acetylene (C2H2): seed effect on SOA yields due to organic photochemistry in the aerosol aqueous phase. Atmos. Chem . Phys. Discuss., 2008. 8: 14841-14892.
4 Liggio, J., S.-M. Li, and R. McLaren, Reactive uptake of glyoxal by particulate matter. J. Geophys. Res. , 2005. 110(D10304): doi: 10.1029/2004JD005113.
5 Ervens, B., G. Feingold, G.J. Frost, and S.M. Kreidenweis, A modeling study of aqueous production of dicarboxylic acids, 1. Chemical pathways and speciated organic mass production. J. Geophys. Res., 2004. 109(D15205): doi: 10.1029/2003JD004387.
6Ervens, B., A.G. Carlton, B.J. Turpin, K.E. Altieri, S.M. Kreidenweis, and G. Feingold, Secondary organic aerosol yields from cloud-processing of isoprene oxidation products. Geophys. Res. Lett., 2008. 35(L02816): doi:10.1029/2007GL031828.