The uncertainties associated with daily, weekly, and day/night sampling of dry-deposition fluxes of SO2 and O3 are addressed, using a multiple-resistance deposition velocity model. Several day/night sampling protocols for both daily and weekly periods are investigated. Inferred fluxes from the various protocols are compared with the average of hourly fluxes computed as the product of the hourly concentration and deposition velocity Vd. For the daily period, day/night sampling gave better estimates of the daily average hourly flux of O3 than the product of the daily average Vd and concentration, but for SO2 the gain in accuracy with greater time resolution was negligible. For the weekly period, day/night sampling for O3 again gave improved estimates over the product of the weekly averaged Vd and concentration. However, fractional errors were on the order of 40%, because Vd and 3 > are positively correlated over weekly periods when the leaf area index is large enough to dominate Vd. For SO2 , day/night sampling provided no improvement over the excellent estimates given by the product of the weekly average Vd and 2 >. ¿American Geophysical Union 1987