Nano-DMA/thermal desorption particle beam mass spectrometric analysis of nanoparticles produced in diesel exhaust

Due to the correlation that was found between atmospheric fine particle (< 2.5μm) mass concentrations and increased human morbidity and mortality, the chemistry of particles produced from diesel engines are of special concern. Diesel engines were known to emit high concentrations of nanoparticles (< 50 nm) and analysis of total diesel aerosol had identified the presence of a number of toxic compounds. However, due to their relatively small mass, chemical analysis was difficult. A nano-differential mobility analyzer was utilized to size select nanoparticles produced from diesel engine exhaust for subsequent chemical analysis by thermal desorption particle beam MS. A number of organic compound classes and sulfuric acid were identified and the approximate molecular weights and vapor pressures verified from calibrated desorption temperatures. Full mass spectra were achieved at the signal peak during desorption for all the 40 and 30 nm particle modes at the 15% engine load condition and for total mode particles at the 50% engine load condition. Mass spectra for standards of the fuel and lubricating oil were also achieved utilizing similar fast-temperature-programmed thermal desorption analysis and were very similar to the diesel particle spectra.