Environ. Scl. Technol. 19a4, 18, 723-726
to empty the pipet is recorded. Flow rate is equal to the pipet volume (1 mL) divided by time (min). Figure 4 shows the calibration curve for flow rate vs. micrometer setting.
Results and Discussion The positive displacement pump feed system was employed with the VOMAG to generate oleic acid aerosols. Operation of the feed system showed reproducibility of flow rate for a given setting of f2.2% or less. The stability of the liquid jet for the operating range indicated that the aerosol produced was highly monodisperse (I). Start up of the Berglund-Liu generator is much easier with the PDP feed system than with the syringe pump feed system. This is due to the much higher operating pressure (up to 100 psig) of the positive displacement pump. Higher operating pressure has also reduced orifice clogging, especially for 5- and 10-pm orifices. Generation time of the VOMAG was increased with the positive displacement pump feed system because of the 30-mL solution reservoir. Continuous generation of up to 8 h has been accomplished, and longer generation times are feasible. The range of flow rates with the positive displacement pump feed system is continuous from 0 to over 1mL/min. This is critical for selecting the optimum flow rate for a given orifice. For example, when a 5 p m orifice is used with the syringe pump feed system, the flow rate can be stepped up from 0.039 to 0.051 mL/min. The optimum flow rate for the 5-pm orifice was between these flow rates. At the 0.039 mL/min flow rate, the orifice would not operate
without clogging within a few minutes. A t the 0.051 mL/min flow rate, the syringe pump would build up too much pressure and disengage from the syringe. The flow rate with the positive displacement pump feed system has been varied from 0.045 to 0.071 mL/min without problems.
Conclusions The PDP feed system has been used to improve the operation of the Berglund-Liu aerosol generator. The modified feed system has reduced clogging of the orifices, provided longer generation time, and provided a wider range of solution flow rates. The positive displacement pump is inexpensive, makes it simple to calibrate flow rates, and can be easily installed in the VOMAG system. Acknowledgments We gratefully acknowledge the assistance of Y. S. Cheng, J. A. Pickrell, J. H. Diel, and H. C. Yeh for technical review of the manuscript and E. E. Goff for illustrations.
Literature Cited (1) Berglund, R. N.; Liu, B. Y. H. Enuiron. Sci. Technol. 1973, 7, 147-153. (2) Wedding, J. B. Enuiron. Sci. Technol. 1975, 9, 673-674. (3) Wedding, J. B.; Stukel, J. J. Enuiron. Sci. Technol. 1974,
8, 456-457. Received for review October 11, 1983. Accepted April 2, 1984. This research was performed under US.Department of Energy Contract DE-ACOI- 76EV01013.
Seasonal Variations in Ambient Atmospheric 1.evels of Formaldehyde and Acetaldehyde Roger L. Tanner' and Zhaokun Meng'
Environmental Chemistry Division, Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973
rn A simple technique is described for determining ambient atmospheric levels of formaldehyde and acetaldehyde by using impinger collection in acidified 2,Cdinitrophenylhydrazine/acetonitrile solution and direct high-pressure liquid chromatography with UV absorbance detection of the corresponding phenylhydrazone solution on reversedphase columns. A limit of detection of -1 ppb for l-h impinger collections is obtained. Data from a coastal NE U.S.site show no discernible diurnal trends, but strong seasonal variations in the levels of both aldehydes are observed, with summer maxima and winter minima. Formaldehyde/acetaldehyde ratios are relatively high (>4) in winter and spring and low (
