Measuring ammonia concentration over a grassland near livestock facilities using a semiconductor ammonia sensor

We demonstrated the effectiveness of a semiconductor ammonia sensor capable of performing diachronic measurements; its characteristics were checked in the laboratory by means including comparison with standard gases. We found as a result that the ammonia sensor's readings increased with increasing water vapor pressure. We compared sensor readings with values obtained by chemical analysis of samples collected in situ and checked sensor reading accuracy. Ammonia concentration was determined by combining ammonia sensor readings with measured values for water vapor pressure. In situ conditions were ammonia concentration of under 100 ppbv and water vapor pressure of 4–16 hPa. There was a good correlation with the concentration of samples trapped with boric acid and analyzed by indophenol colorimetry. We discerned a relationship between ammonia concentration and local meteorological conditions such as wind direction and speed. The estimated error of the ammonia sensor's measurements was ±9.7 ppbv when ammonia concentration as measured by acid sampling and colorimetry was regarded as correct. This demonstrated that it is possible to detect in situ fluctuations in low ammonia concentrations of about 10 ppbv, which was the background concentration in farming areas. We have shown a monitoring method for ammonia in situ that is both easy to operate and low-cost.