Size Resolved Chemical Composition of Automobile Generated Aerosol Via Single Particle Real-Time Ion-Trap Mass-Spectrometry
EMSL Project ID
2549
Abstract
Single Particle Mass Spectroscopy (SPMS) and Exhaust Emissions SPMS are particularly suited to address the combustion engine industry need to characterize particulate emissions. As discussed below, SPMS can provide a detailed correlation between engine and fuel performance and aerosol properties. SPMS will make it possible to produce a detailed accounting of particle composition and size as a function of time and distance from the point of emission. These data will help in the development of a model describing the physical and chemical processes that these particles undergo as the emissions are transported and mixed with the ambient atmosphere. Here SPMS offers a unique advantage because of their inherent single particle sensitivity it is possible to unambiguously distinguish combustion particles from among the many ambient particles and investigate their time dependent properties. Single particle instruments use a UV laser to vaporize individual particles and produce ions for time of flight mass analysis. The vaporization ionization process also known as ablation is highly nonlinear and nonspecific. Organic compounds tend to be most sensitive to the ablation process, producing a high degree of fragmentation that can vary drastically from one particle to the next. This high degree of variability presenting an insurmountable difficulty for the analysis, which for real-atmosphere particles is further amplified due to the presence of a number of organic compounds in each particle. To resolve this problem we at BNL have recently developed an experimental approach in which infrared laser heating results in particle evaporation and a UV laser is used to ionize the gas plume, thereby eliminating the highly nonlinear response inherent in ablation. The resultant spectra are reproducible and quantitative. However, the compositions of exhaust aerosol tend to be complex, containing inorganic compounds, elemental carbon and a large number of organic compounds many of which are semi-volatile. While most present SPMS can readily distinguish between the three classes and quantify their presence as a function of particle size and distance from the emission source because of fragmentation during ionization a molecular level analysis of the organic fraction is not possible. This problem presents a challenge that requires a novel approach that has the capability to eliminate the high degree of fragmentation inherent in most ionization techniques. We propose to test the application of chemical ionization in an ion trap to single particle mass spectroscopy. Here pre-stored H3O+ will be allowed to react with the gas plume that is produced by evaporating a single particle inside the trap protonating the organic fraction of the particle composition to be analyzed by mass spectroscopy. This very same chemistry has recently been applied to the detection and characterization of ambient volatile organic compounds using quadruple mass spectroscopy. We will be taking advantage of equipment and expertise which is unique to PNL. Mike Alexander is a leading expert in ion trap mass spectrometry while at the time he has developed the expertise in proton transfer ionization techniques as applied to trace gas measurements.
Project Details
Project type
Exploratory Research
Start Date
2002-07-18
End Date
2004-07-20
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Cai Y, AN Zelenyuk, and DG Imre. 2006. "A High Resolution Study of the Effect of Morphology on the Mass Spectra of Single PSL Particles with Na-Containing Layers and Nodules." Aerosol Science and Technology 40(12):1111-1122. doi:10.1080/02786820601001677