Abstract
Abstract. In this paper we present the continued development of the miniDOAS, an active differential optical absorption spectroscopy (DOAS) instrument used to measure ammonia concentrations in ambient air. The miniDOAS has been adapted for use in the Dutch National Air Quality Monitoring Network. The miniDOAS replaces the life-expired continuous-flow denuder ammonia monitor (AMOR). From September 2014 to December 2015, both instruments measured in parallel before the change from AMOR to miniDOAS was made. The instruments were deployed at six monitoring stations throughout the Netherlands. We report on the results of this intercomparison. Both instruments show a good uptime of ca. 90 %, adequate for an automatic monitoring network. Although both instruments produce 1 min values of ammonia concentrations, a direct comparison on short timescales such as minutes or hours does not give meaningful results because the AMOR response to changing ammonia concentrations is slow. Comparisons between daily and monthly values show good agreement. For monthly averages, we find a small average offset of 0.65 ± 0.28 µg m−3 and a slope of 1.034 ± 0.028, with the miniDOAS measuring slightly higher than the AMOR. The fast time resolution of the miniDOAS makes the instrument suitable not only for monitoring but also for process studies.
Highlights
Ammonia in the ambient air plays an important role in the formation of aerosols (Asman, 1998) through reactions with nitrogen oxides or sulfur dioxide
We find a small average offset of 0.65 ± 0.28 μg m−3 and a slope of 1.034 ± 0.028, with the miniDOAS measuring slightly higher than the ammonia monitor (AMOR)
This paper describes the implementation and performance of the miniDOAS, the intercomparison with the AMOR and some issues associated with the transition
Summary
Ammonia in the ambient air plays an important role in the formation of aerosols (Asman, 1998) through reactions with nitrogen oxides or sulfur dioxide. These aerosols contribute to the total burden of particulate matter and may have public health effects (Fischer et al, 2015). An ammonia monitoring network has been in operation in the Netherlands since 1992, providing hourly concentration measurements, currently at six locations. These measurements are part of the Dutch National Air Quality Monitoring Network
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