The Central Valley in California has historically had high levels of atmospheric particulate matter (PM), resulting in significant adverse health effects. Three sources of atmospheric PM in the Central Valley are vehicle exhaust emissions, agricultural activity and residential wood burning. Laser desorption ionization time-of-flight mass spectrometry (LDI-TOF MS) and radiocarbon accelerator mass spectrometry (AMS) were performed on size fractionated atmospheric PM collected in Davis using a DRUM impact analyzer. The radiocarbon AMS analysis showed that the size fractionated total carbonaceous particulate matter was mainly biogenic in origin, having an average fraction modern (Fm14C) = 0.753 � 0.006. The Fm14C from both sample collections were similar and there wasn't a significant change in fraction modern as particle size decreased. The high fraction modern in the small PM points to the secondary organic aerosol being biogenic in origin. The data suggests the elemental carbon found in the large size fraction is biogenic, possibly from agricultural activity.  The LDI-TOF MS results show that as particle size decreases the amount of organic carbon increases with approximately 70% of the LDI-TOF signal intensity in the smallest size fraction (0.09 � 1.2 �m) coming from oxidized  hydrocarbons. Three distinct chemical composition modes were observed in the LDI-TOF analysis:  0.09 to 0.34 �m, 0.34 to 0.56 �m and >0.56 �m. The particles 0.5 �m. The chemical difference in the PM is driven by the large amount of secondary organic aerosol. The difference in the chemical composition between the respirable and larger PM needs to be considered when associating health effects with PM exposure. Overall, the size fractionated PM was found to be a mixture of organic and elemental carbon originating from mainly modern carbon sources.

Chemical speciation and source apportionment of size fractionated aerosols collected in the Central Valley

248th National Meeting (2014)

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