Abstract Number: 666 Working Group: Instrumentation and Methods
Abstract A particle trap laser desorption mass spectrometer (PT-LDMS) has been developed for online measurements of sulfate, nitrate, and organic carbon. The main components of the instrument include an aerodynamic lens, a particle trap and cell, an electron impact ionization quadrupole mass spectrometer (QMS), and a carbon dioxide (CO2) laser. The first prototype of PT-LDMS successfully demonstrated the proof of concept (Takegawa et al. AST, 2012). The instrument has been redesigned and reconstructed to reduce the size and weight and also to achieve automated measurements (Takeda et al., AAAR meeting, 2012). This study presents further improvement of the second prototype, focusing on the temporal profile of laser irradiation and cooling of the particle trap during particle collection. The improvement of laser profile is critical for the quantification of ammonium sulfate (AS) because thermal decomposition process of AS significantly depends on the desorption temperature and heating rate. We have tested a number of temporal profiles of laser irradiation and found that the yield of m/z 48 signals from AS can be increased by a factor of 5 compare to the first prototype. The improvement of cooling method is critical for the quantification of semi-volatile compounds such as ammonium nitrate (AN) and some organic compounds. We have newly designed a particle trap holder that has a much better thermal conductivity than the previous version. As a result, the time required for cooling the particle trap after laser irradiation has been drastically reduced. Results from laboratory experiments and ambient intercomparison will be presented and discussed.