Aerosol Spectrometer for Measuring Diameters and Chemical Compositions of Particulate Organic Matter: II. Lower Detection Limit

摘要

We describe the improvement in the sensitivity of an aerosol spectrometer that simultaneously measures the size-dependent concentration and chemical composition of particulate organic matter. The spectrometer studied in the present work consists of a differential mobility analyzer (DMA) for the size classification and a gas chromatography mass spectrometer (GC-MS) for the composition analysis. Size-classified particles of hydrocarbons were directly introduced into a thermal desorption (TD) tube packed with absorbent. Hydrocarbon molecules thermally desorbed from the TD tube were then introduced into the GC-MS. We improved the vacuum level in the ion source section of the GC-MS by changing the GC-MS carrier gas, and increased the velocity of carrier gas that expelled the hydrocarbon vapor from the TD tube into the GC-MS by reducing the size of the pipe. For a particle size of 330 nm, the detection sensitivity of the spectrometer for nonylbenzene particles was approximately 30 times as high as that of the spectrometer developed in our previous work (Okada et al., 2012). From the results of our investigation of the adsorption and desorption efficiency of the TD tube and the lower detection limit of the GC-MS using nonylbenzene vapor as a sample, we found that nonylbenzene weighing more than 6.6x10~(-2) ng could be measured with our spectrometer, i.e., the lower detection limit.