AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Primary to Secondary Organic Aerosol: Evolution of Emissions from Combustion Sources
ALBERT A. PRESTO, Timothy Gordon, Christopher Hennigan, Marissa Miracolo, Allen Robinson, Carnegie Mellon University
Abstract Number: 31 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Mobile combustion sources such as automobiles and diesel trucks contribute to ambient organic aerosol in two ways. These sources directly emit primary organic aerosol (POA). The photo-oxidation of organic vapors that are co-emitted with the POA produces secondary organic aerosol (SOA). Several studies [1-3] have shown that SOA formation from the photo-oxidation of diluted exhaust is larger than POA emissions by a factor of 4-50. This importance of SOA from mobile sources is consistent with ambient AMS measurements that indicate SOA, in the form of the various OOA factors, dominates ambient organic aerosol in nearly all environments. [4]
This presentation investigates the evolution of the aerosol mass spectra of dilute POA and the resultant SOA from smog chamber experiments conducted with various combustion sources, including gasoline automobiles, diesel trucks, gas-turbine engines, and wood smoke measured with an Aerodyne quadrupole AMS. Contributions and mass spectra of SOA and POA are estimated using Positive Matrix Factorization [5] and analyzed using the f$_(44)/f$_(43) triangle of Ng et al. [6, 7]
The gasoline and diesel data can be explained with two PMF factors – one for POA and one for SOA. The determination of a single SOA factor suggests that SOA formed in the chamber is dominated by “first-generation” chemistry, consistent with an effective atmospheric timescale of several hours. The experiments do not have significant multi-generational chemistry or oxidative aging that would occur over several days. The POA factor is spectrally similar to the ambient HOA factor, with high f$_(43) (~0.07 – 0.1) and low f$_(44) (<0.05). The SOA factors have higher f$_(44) and lower f$_(43) and are spectrally similar to mildly oxidized SV-OOA. When plotted in Van Krevelen space, the SOA and POA factors exhibit a slope of approximately -0.5. This suggests that SOA formation chemistry in these experiments includes the addition of both acid and alcohol/peroxide functional groups, and is chemically similar to ambient SOA. [6]
1. Chirico, R., et al., Atmos. Chem. Phys., 2010. 10: p. 11545-11563.
2. Miracolo, M.A., et al., Environ. Sci. Technol., submitted.
3. Miracolo, M.A., et al., Atmos. Chem. Phys., 2011. 11: p. 4135-4147.
4. Zhang, Q., et al., Geophys. Res. Lett., 2007. 34: p. L13801.
5. Ulbrich, I.M., et al., Atmos. Chem. Phys., 2009. 9: p. 2891-2918.
6. Ng, N.L., et al., Atmos. Chem. Phys., 2011. 11: p. 6465-6474.
7. Ng, N.L., et al., Atmos. Chem. Phys., 2010. 10: p. 4625-4641.