The backward Lagrangian stochastic (BLS) model and open-path tunable diode laser (OPTDL) analyzer were used to monitor ammonia (NH3) emissions from urea applied to winter wheat in the North China Plain. The high-temporal resolution measurements of ammonia concentrations provided an opportunity for estimating the diel patterns of ammonia emissions, as well as valuable information about the factors that influence NH3 emissions. The results showed both large diel variability and daily variability in NH3 volatilization, with NH3 emissions highest during the daytime. The diel pattern of ammonia volatilization depended mainly on the diel variation of wind speed and soil temperature, while the overall pattern of NH3 loss was strongly affected by soil moisture content, soil NH4 (+)-N concentration, wind speed and soil temperature. At the end of the measurement period, the cumulative NH3 loss was 12.21-16.43 kg N ha(-1), calculated based on different time scale average Q (BLS). Due to sensitivity of the OPTDL analyzer, the estimated total ammonia loss was still doubtful in this study.
