Gas-to-particle conversion processes

The atmospheric chemistry of volatile organic compounds (VOCs) can act as a source for secondary organic aerosol, SOA that is expected to exert a cooling of the atmosphere. SOA formation is linked with debates about air quality, visibility, public health, climate, and the oxidative capacity of the atmosphere.

The accurate simulation of SOA formation in the atmosphere is recently being questioned as a growing body of evidence shows large discrepancies in comparison of model results with observations in different and large compartments of the atmosphere, including polluted urban air (Volkamer et al., 2006), the outflow of pollution sources (de Gouw et al., 2005; Johnson et al., 2006) and compartments of the free troposphere (Heald et al., 2005). Given the magnitude of underestimation of SOA production from current SOA models (factor 5-100) little trust can be inferred that we understand the sources of SOA. The significant gaps in our understanding of SOA formation are a priority topic of current atmospheric chemistry research.

Field observations in Mexico City suggest that a missing sink exists for gas-phase glyoxal, a very volatile product of VOC oxidation. This sink can explain a significant portion of the missing SOA source in Mexico City (Volkamer et al., 2007 in preparation), suggesting that it may be chemical rather than physical processes that control SOA formation. Specific laboratory experiments will focus on understanding the controlling factors of the chemical reactivity of glyoxal in particles.

Figure 1. Differences in predicted and modelled SOA formation from four field campaigns: NEAQS 2002 (deGouw et al., 2005), ACE-Asia 2001 (Heald et al., 2005), TORCH 2003 (Johnson et al., 2006), MCMA-2003 (Volkamer et al., 2006). Adopted from (Volkamer et al., 2006).

References

de Gouw, J. A., Middlebrook, A. M., Warneke, C., Goldan, P. D., Kuster, W. C., Roberts, J. M., Fehsenfeld, F. C., Worsnop, D. R., Canagaratna, M. R., Pszenny, A. A. P., Keene, W. C., Marchewka, M., Bertman, S. B. and Bates, T. S. (2005). Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002, Journal of Geophysical Research, 110, D16305, doi:10.1029/2004JD005623.

Heald, C. L., D. J. Jacob, R. J. Park, L. M. Russel, B. J. Huebert, J. H. Seinfeld, H. Liao, and R. J. Weber (2005). A large organic aerosol source in the free troposphere missing from current models, Geophysical Research Letters, 32, L18809.

Johnson, D., S. R. Utembe, M. J. Jenkin, R. G. Derwent, G. D. Hayman, M. R. Alfarra, H. Coe, and G. McFiggans (2006). Simulating regional scale secondary organic aerosol formation during the TORCH 2003 campaign in the southern UK, Atmospheric Chemistry and Physics, 6, 403-418.

Volkamer, R., Jimenez, J. L., San Martini, F., Dzepina, K., Zhang, Q., Salcedo, D., Molina, L. T., Worsnop, D. R. and Molina, M. J. (2006). Secondary organic aerosol formation from anthropogenic air pollution: Rapid and higher than expected, Geophysical Research Letters, 33, L17811, doi:10.1029/2006GL026899.