Measuring ammonia emissions from vegetable greenhouses with an inverse dispersion technique

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Abstract China’s greenhouse vegetable production is considered an important contributor to the national ammonia (NH3) inventory because of the excess nitrogen (N) application rate (normally over 1000 N kg ha−1 yr−1) and large N consumption (approximately 10% of the N fertilizer in China). However, the previously measured emission rates are still in question because of the inherent limits of the commonly used techniques (e.g., non-flow-through chamber technique) and the exclusion of the impact of the greenhouse opening/enclosing scheme on NH3 loss from greenhouse soil to the atmosphere over a growing season. This study examines the ability of an inverse dispersion technique, in combination with an open-path laser system, for measuring NH3 emissions from vegetable greenhouses. The NH3 concentrations over the greenhouse areas greatly exceeded the laser’s detectable limit and showed a clear diel variation pattern. Determination of the area and height of the greenhouse sources are critical to emission estimates, while removing the periods with inaccurate wind simulations has minimal effect on the daily and total emission estimations since the omitted periods mainly occurred during nighttime (low emission periods). With the application of our findings, the observed diel NH3 emission patterns are found in good agreement with the air temperature. The NH3-N losses during the measurements in terms of proportions to the N fertilization (40.02% in spring, 7.83% in summer) are generally comparable to those of previous studies. Overall, the inverse dispersion technique can be used to provide good NH3 emission estimates as well as to assess NH3 emission factors along the opening/enclosing scheme across a growing season of greenhouse vegetables in the future.