Comparison of backward Lagrangian stochastic model with micrometeorological mass balance method for measuring ammonia emissions from rice field

Abstract

A field experiment was conducted to assess the accuracy of the backward Lagrangian stochastic (BLS) model combined with an open-path tunable diode laser (OPTDL) system for estimating ammonia emissions from rice field by comparing with the micrometeorological mass balance (MMB) method. During the experimental period, the average height of rice was 0.65 m, and the average height of laser path was 1.3 m. The results showed that there was no significant difference between the ammonia emission rates estimated by the two methods, indicating no significant effect of tall rice on the accuracy of the BLS model. The high temporal resolution data showed that ammonia emissions had a dramatic diurnal cycle: rise at daytime and fall at night. Although the OPTDL technique was not able to measure ammonia concentrations at low emission rates due to relatively high detection limit, the total ammonia loss estimated by the BLS model was not significant different from that of the MMB method. The results demonstrate the effectiveness of the BLS model with the OPTDL technique for estimating ammonia emissions from farmland covered with tall vegetation. Within the acceptable accuracy, the relatively low laser path height is recommended for farmland with tall vegetation due to relatively high detection limit of the OPTDL technique and low ammonia concentration of farmland.