WEEKLY AND DAILY PRECIPITATION CHEMISTRY NETWORK COMPARISONS IN THE EASTERN US - NADP NTN VS MAP3S/AIRMON/

This study is a comparison of the weekly aggregated MAP3S (1981-1989) and AIRMoN (1992-1995) daily precipitation chemistry record, to the NA DP/NTN weekly data at four collocated sites in the eastern U.S.A. Data for conductivity, H+, NO3-, and SO42- all strongly support the hypoth esis that the weekly and daily network concentrations of these ions ar e comparable for both time periods. Data for ammonium show a statistic ally significant bias for both time periods with the daily record havi ng concentrations approximately 14% higher than the weekly values. Thi s bias also has been observed in other studies of weekly and daily net works, and may be a function of residence time samples remain in the f ield and/or in storage before analysis. Significantly higher Cl- and K + concentrations in the MAP3S data set from 1986 to 1989 suggest a con tamination problem and use of these data is not recommended for this t ime period. Potassium concentrations during the other years of record compare poorly between the daily and weekly networks on a weekly basis . Annual data compare well. The other base cation weekly concentration s (Ca2+, Mg2+, Na+) also do not compare well, with average weekly diff erences ranging from 23 to 51%. However, both the daily and weekly net works show a very similar temporal decline in the sum of base cation c oncentrations of about 30% from the periods 1981-1985 to 1992-1995. Ne twork Ca2+ and Mg2+ concentration trends also compare well for the ent ire period of record. Intranetwork variability, assessed in a separate study at several collocated NADP sites in the eastern U.S.A., could a ccount for 1/5 to 1/2 of the internetwork bias for most ions. Intranet work relative error may account for 1/4 to 2/3 of the internetwork rel ative error. This study supports the concept that the MAP3S and AIRMoN networks represent a continuous event/daily network data base of high quality for conductivity, H+, NO3-, and SO42- concentrations. Compari sons in trends of NH4+, Ca2+ and Mg2+ also suggest that these ions rep resent a quality long-term database. Daily network NH4+ (and possibly Na+) concentrations may be better estimates of actual precipitation co ncentrations than the weekly network data. (C) 1998 Elsevier Science L td. All rights reserved.