An automatic atmospheric ammonia network in the Netherlands : set-up and results

Abstract A combination of measuring and modelling is used as an assessment strategy for the description of the atmospheric ammonia concentration field and the ammonium deposition field throughout the Netherlands. To support this strategy, a monitoring network for the automatic measurement of atmospheric ammonia concentrations was considered to be essential. A field intercomparison test and a further study in the laboratory revealed that continuous-flow denuders met most of a set of predefined instrumental and network performance criteria. A monitoring network of eight sites for the continuous automatic measurement of ammonia with continuous-flow denuders was established in the Netherlands in 1992. The network performed fairly well, with an average measurement data return rate of 90%. Annual means in the Netherlands range from 2–4 μg NH 3  m -3 in background areas to 10–25 μg NH 3  m -3 in ammonia emission areas; 98 percentiles of hourly values range from 10 to 100 μg NH 3  m -3 . Measurement results show clear seasonal and diurnal variations. Calculated mean concentrations correlate fairly well with measured concentrations. Instrument development work was continued to upgrade the network’s operational characteristics. New instruments with lower maintenance frequency, on-line technical status control and automatic data retrieval have recently been deployed in the Dutch National Air Quality Monitoring Network.