Abstract
Abstract. Atmospheric levels of ammonia (NH3) have substantially increased during the last century, posing a hazard to both human health and environmental quality. The atmospheric budget of NH3, however, is still highly uncertain due to an overall lack of observations. Satellite observations of atmospheric NH3 may help us in the current observational and knowledge gaps. Recent observations of the Cross-track Infrared Sounder (CrIS) provide us with daily, global distributions of NH3. In this study, the CrIS NH3 product is assimilated into the LOTOS-EUROS chemistry transport model using two different methods aimed at improving the modeled spatiotemporal NH3 distributions. In the first method NH3 surface concentrations from CrIS are used to fit spatially varying NH3 emission time factors to redistribute model input NH3 emissions over the year. The second method uses the CrIS NH3 profile to adjust the NH3 emissions using a local ensemble transform Kalman filter (LETKF) in a top-down approach. The two methods are tested separately and combined, focusing on a region in western Europe (Germany, Belgium and the Netherlands). In this region, the mean CrIS NH3 total columns were up to a factor 2 higher than the simulated NH3 columns between 2014 and 2018, which, after assimilating the CrIS NH3 columns using the LETKF algorithm, led to an increase in the total NH3 emissions of up to approximately 30 %. Our results illustrate that CrIS NH3 observations can be used successfully to estimate spatially variable NH3 time factors and improve NH3 emission distributions temporally, especially in spring (March to May). Moreover, the use of the CrIS-based NH3 time factors resulted in an improved comparison with the onset and duration of the NH3 spring peak observed at observation sites at hourly resolution in the Netherlands. Assimilation of the CrIS NH3 columns with the LETKF algorithm is mainly advantageous for improving the spatial concentration distribution of the modeled NH3 fields. Compared to in situ observations, a combination of both methods led to the most significant improvements in modeled monthly NH3 surface concentration and NH4+ wet deposition fields, illustrating the usefulness of the CrIS NH3 products to improve the temporal representativity of the model and better constrain the budget in agricultural areas.
Highlights
Ammonia (NH3) is an alkaline gas in the Earth’s atmosphere
The simulated NH3 concentrations from the default run in LOTOS-EUROS were sampled at the locations of the Cross-track Infrared Sounder (CrIS) observations, and after application of the averaging kernels they were compared with the retrievals
The CrIS NH3 product is integrated into the LOTOS-EUROS chemical transport model using two different methods
Summary
NH3 is highly reactive and readily reacts with available acids, forming aerosol components harmful to human health (Pope et al, 2009; Lelieveld et al, 2015; Giannakis et al, 2019) and, directly and indirectly, impacting global climate change (Erisman et al, 2011; Myhre et al, 2013). Agricultural emissions of NH3 consist of, among others, volatilized NH3 after manure and chemical fertilizer application, livestock housing and grazing, and harvesting of crops. About 40 % of the total global NH3 emissions follow directly from volatilization of animal manure and chemical fertilizer, a spatially variable process highly controlled by the temperature and acidity of soils (Sutton et al, 2013). After the emitted NH3 is transported through the atmosphere, it is deposited back to the Earth’s surface through the processes of wet and dry deposition. Excess amounts of reactive nitrogen deposition can cause several adverse effects, such as eutrophication in aquatic ecosystems and soil acidification (Erisman et al, 2007) and biodiversity loss in terrestrial ecosystems (Bobbink et al, 2010)
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