EXPOSURE OF DEACIDIFIED AND UNTREATED PAPER TO AMBIENT LEVELS OF SULFUR DIOXIDE AND NITROGEN DIOXIDE: NATURE AND YIELDS OF REACTION PRODUCTS
EDWIN L. WILLIAMS, & DANIEL GROSJEAN
1.1 MEASUREMENT UNCERTAINTIES
Uncertainties in nitrite, nitrate, and sulfate concentrations were calculated by propagation of errors. Linear calibration plots of peak height vs. μg of analyte injected were prepared each day samples were analyzed. The slopes and intercepts of the calibration plots were used to calculate the analyte concentration:
where C is the analyte concentration in μg, P is the peak height in mm, S is the slope of the calibration plot in μg/mm, and I is the intercept of the calibration plot in μg. The uncertainty in the analyte concentration, σC, is given by:
where σP is the uncertainty in the analyte peak height, σs is the uncertainty in the calibration slope (one standard deviation), and σI is the uncertainty in the calibration intercept (one standard deviation). The mean relative standard deviation (RSD) of the peak height from replicate injections was used to estimate σP. Mean RDSs were 3.3% for nitrite, 13.9% for nitrate, and 10.1% for sulfate (10, 17, and 17 sets of replicates, respectively).
Refrigerated controls and extraction solvent blanks contained some sulfate and nitrate but no nitrite. Thus, for nitrite, σC could be estimated directly from equation E2 and ranged from 1 to 8 μg per sample (equivalent to 5–19% for samples containing more than 10 μg nitrite). For nitrate and sulfate, concentrations in the paper samples were calculated by subtracting the nitrate and sulfate concentrations of the refrigerated controls and solvent blanks from the measured concentrations as follows:
where X is the corrected analyte concentration in μg, A is the analyte concentration in μg, R is the analyte concentration of the refrigerator controls; and B is the analyte concentration of the solvent blanks. The uncertainty in X, σx, is given by:
where σA, σR, and σB are the uncertainties in the analyte concentration of the paper sample, the refrigerated control, and the solvent blank, respectively. For nitrate, uncertainties calculated using equation E4 ranged between 1 and 6 μg per sample (5–27% for samples containing more than 10 μg nitrate), with a mean of 3 μg. For sulfate, uncertainties ranged between 5 and 32 μg per sample (2–63% for samples containing more than 10 μg sulfate), with a mean of 16 μg.
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EDWIN L. WILLIAMS II holds a M.S. degree in physical chemistry from the University of California, Los Angeles, and is a research scientist with DGA, Inc. Address: DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, Calif. 93003.
DANIEL GROSJEAN holds a docteur es sciences degree in physical organic chemistry from the University of Paris and has done postdoctoral research at the California Institute of Technology, Pasadena, California. He is president of DGA, Inc., a private environmental research company founded in 1983 and directs research studies in atmospheric chemistry, air pollution measurements, museum air quality, and art conservation. Address: DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, Calif. 93003.