Evaluation of recently-proposed secondary organic aerosol models for a case study in Mexico City 1Cooperative Institute for Research in the Environmental Sciences (CIRES), Univ. of Colorado at Boulder, Boulder, CO, USA
2Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO, USA
3National Center for Atmospheric Research – Atmospheric Chemistry Division, Boulder, CO, USA
4Meteo France/CNRM-GAME, Toulouse, France
5Atmospheric Sciences Research Center, University at Albany, SUNY, Albany, NY, USA
6Department of Civil and Environmental Engineering, University of California at Davis, Davis, CA, USA
7Air Pollution Research Center, University of California, Riverside, CA, USA
Received: 08 Dec 2008 – Published in Atmos. Chem. Phys. Discuss.: 17 Feb 2009 – Published: 10 Aug 2009Abstract. Recent field studies have found large discrepancies in the measured vs.
modeled SOA mass loadings in both urban and regional polluted atmospheres.
The reasons for these large differences are unclear. Here we revisit a case
study of SOA formation in Mexico City described by Volkamer et al. (2006),
during a photochemically active period when the impact of regional biomass
burning is minor or negligible, and show that the observed increase in OA/ΔCO
is consistent with results from several groups during MILAGRO 2006. Then we
use the case study to evaluate three new SOA models: 1) the update of
aromatic SOA yields from recent chamber experiments (Ng et al., 2007); 2)
the formation of SOA from glyoxal (Volkamer et al., 2007a); and 3) the
formation of SOA from primary semivolatile and intermediate volatility
species (P-S/IVOC) (Robinson et al., 2007). We also evaluate the effect of
reduced partitioning of SOA into POA (Song et al., 2007). Traditional SOA
precursors (mainly aromatics) by themselves still fail to produce enough SOA
to match the observations by a factor of ~7. The new low-NOx
aromatic pathways with very high SOA yields make a very small contribution
in this high-NOx urban environment as the RO2·+NO reaction
dominates the fate of the RO2· radicals. Glyoxal contributes several
μg m−3 to SOA formation, with similar timing as the measurements.
P-S/IVOC are estimated from equilibrium with emitted POA, and introduce a
large amount of gas-phase oxidizable carbon that was not in models before.
With the formulation in Robinson et al. (2007) these species have a high SOA
yield, and this mechanism can close the gap in SOA mass between measurements
and models in our case study. However the volatility of SOA produced in the
model is too high and the O/C ratio is somewhat lower than observations.
Glyoxal SOA helps to bring the O/C ratio of predicted and observed SOA into
better agreement. The sensitivities of the model to some key uncertain
parameters are evaluated.
Citation: Dzepina, K., Volkamer, R. M., Madronich, S., Tulet, P., Ulbrich, I. M., Zhang, Q., Cappa, C. D., Ziemann, P. J., and Jimenez, J. L.: Evaluation of recently-proposed secondary organic aerosol models for a case study in Mexico City, Atmos. Chem. Phys., 9, 5681-5709, doi:10.5194/acp-9-5681-2009, 2009.