Abstract
The present study aimed at elucidating the effects of time resolution of air concentration on the estimated exchange fluxes of ammonia (NH3) and particulate ammonium (pNH4) by a gradient method. Observation of their exchange fluxes was conducted at an upland filed in Hokkaido in spring in 2008 and 2009. The filter-pack method was applied to measure the air concentrations. Measurement frequencies were once to three times during daytime and once during nighttime. The errors in estimated fluxes by averaging the air concentrations during daytime were small both for NH3 and pNH4; however, the significant emission of NH3 due to the manure application resulted in a relatively large error. By contrast, the error in estimated fluxes by averaging the air concentrations during a day was large for NH3, which underestimated the exchange fluxes by 30% in average. It was concluded that day-night separation was indispensable for reducing the errors in estimated fluxes of NH3. The day-night separation was also effective in estimating a weekly mean flux.
