Secondary organic aerosol formation in automobile exhaust, investigated by mass spectrometry.

Abstract The behavior of automobile exhaust is well known through combustion science, but the potential health and environmental risks of secondary exhaust particles (created by solar irradiation) and soot are less well understood. Primary pollutants (raw exhaust) react in the atmosphere when irradiated by the Sun creating secondary pollutants (Secondary organic aerosols, SOA). The purpose of this work is to investigate the creation of exhaust SOA. This project is divided into three steps. First the content of exhaust is investigated using a quadrupole mass spectrometer (QMS) in order to establish the content and a storage method of an exhaust sample. Second, synchrotron radiation and a multichannel time of flight spectrometer (MCTOF) are used to study photolysis of exhaust. In this work the creation of exhaust SOA could not be verified, it can be a matter of detection technique or the fact that none was created. Third, benzene, a molecule known to form SOA [1] was investigated in order to establish what to search for in future exhaust studies. A software program called ANACONDA was used to identify the different masses and fragmentation of the appearing compounds. In earlier studies of exhaust, the $C_3H_3^+$ and $C_5H_3^+$ fragments were found and identified to come from aromatics [1]. In this work it was found that those two fragments occur in the benzene experiments, confirming that those fragments belong to benzene. It was also found that the behavior of benzene undergoing photolysis in both the UV and X-ray region agrees with earlier studies [2][3]. The UV-region is most relevant in this work since it occurs in the atmosphere, but the X-ray region was studied briefly for comparison. (Less)