Measuring ammonia concentration over a grassland near livestock facilitiesusing 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 w ater vapor pressure. We compared sensor readings with values obtained by ch emical analysis of samples collected in situ and checked sensor reading acc uracy. Ammonia concentration was determined by combining ammonia sensor rea dings with measured values for water vapor pressure. In situ conditions wer e 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 rel ationship between ammonia concentration and local meteorological conditions such as wind direction and speed. The estimated error of the ammonia senso r's measurements was +/- 9.7 ppbv when ammonia concentration as measured by acid sampling and colorimetry was regarded as correct. This demonstrated t hat it is possible to detect in situ fluctuations in low ammonia concentrat ions of about 10 ppbv, which was the background concentration in farming ar eas. We have shown a monitoring method for ammonia in situ that is both eas y to operate and low-cost. (C) 2001 Elsevier Science Ltd. All rights reserv ed.