Analysis of Directly Sampled Natural Aerosols

A rapid sampling method for direct aerosol analysis using FD-mass spectrometer has been described . In a predominantly inorganic aerosol three alkali metal cations and a number of cluster ions of intact salts have been identified under the conditions of high mass resolution (R 15,000, 10 per cent valley definition) using photographic registration. 

The stereoscan micrograph of the FD emitter used in Fig. 16 shows the branched structure of carbonaceous needles grown on the 10 pm tungsten wire at high enlargement. The micrograph-was taken after a 4-hour exposure to natural air in the jet collector, at a flow rate of 3 1 min Numerous solid particles were caught in the dendritic emitter. 

After exposure to the air blast the loaded field emitter is directly transferred into the mass spectrometer and pumped to 10 Torr. A trace of acetone is injected into the ion source to optimize the ion current by adjusting the emitter in front of the slotted cathode plate of the speetrometer. The mass spectrum of the sample is then recorded on a photoplate. 

Forty one lines are observed in the spectrum of the aerosol 36 of which can be assigned to ions of inorganic salts and to cluster ions of these salts (Table 6). Several intense lines are accompanied by weaker signals which are attributed to less 

The inspection of Table 6 shows that Na , K, NH/ and a trace of Rb are present as cations in the aerosol. Rubidium is detected as a natural trace element in potassium salts. The densitometer readings provide approximate information on the relative abundances, although ammonium compounds may be underestimated due to some evaporation of their neutral components, especially at higher temperatures. The only anions detected in the aerosol are NOj , SO , HSO and Cl . The predominance of the nitrate ion is noteworthy, stressing the importance of aerosols as a sink for NO2 in the atmosphere. NO2 has been shown to react rapidly with NaCl to form NaNOj and NOCl as an intermediate of presumably short lifetime in the atmosphere. The product NaNOj is most abundantly observed in the aerosol, besides some unreacted NaCl. 

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