An evaluation of European nitrogen and sulfur wet deposition and their trends estimated by six chemistry transport models for the period 1990–2010

Abstract

Abstract. The wet deposition of nitrogen and sulfur in Europe for the period 1990–2010 was estimated by six atmospheric chemistry transport models (CHIMERE, CMAQ, EMEP MSC-W, LOTOS-EUROS, MATCH and MINNI) within the framework of the EURODELTA-Trends model intercomparison. The simulated wet deposition and its trends for two 11-year periods (1990–2000 and 2000–2010) were evaluated using data from observations from the EMEP European monitoring network. For annual wet deposition of oxidised nitrogen (WNOx), model bias was within 30 % of the average of the observations for most models. There was a tendency for most models to underestimate annual wet deposition of reduced nitrogen (WNHx), although the model bias was within 40 % of the average of the observations. Model bias for WNHx was inversely correlated with model bias for atmospheric concentrations of NH3+NH4+, suggesting that an underestimation of wet deposition partially contributed to an overestimation of atmospheric concentrations. Model bias was also within about 40 % of the average of the observations for the annual wet deposition of sulfur (WSOx) for most models. Decreasing trends in WNOx were observed at most sites for both 11-year periods, with larger trends, on average, for the second period. The models also estimated predominantly decreasing trends at the monitoring sites and all but one of the models estimated larger trends, on average, for the second period. Decreasing trends were also observed at most sites for WNHx, although larger trends, on average, were observed for the first period. This pattern was not reproduced by the models, which estimated smaller decreasing trends, on average, than those observed or even small increasing trends. The largest observed trends were for WSOx, with decreasing trends at more than 80 % of the sites. On average, the observed trends were larger for the first period. All models were able to reproduce this pattern, although some models underestimated the trends (by up to a factor of 4) and others overestimated them (by up to 40 %), on average. These biases in modelled trends were directly related to the tendency of the models to under- or overestimate annual wet deposition and were smaller for the relative trends (expressed as % yr−1 relative to the deposition at the start of the period). The fact that model biases were fairly constant throughout the time series makes it possible to improve the predictions of wet deposition for future scenarios by adjusting the model estimates using a bias correction calculated from past observations. An analysis of the contributions of various factors to the modelled trends suggests that the predominantly decreasing trends in wet deposition are mostly due to reductions in emissions of the precursors NOx, NH3 and SOx. However, changes in meteorology (e.g. precipitation) and other (non-linear) interactions partially offset the decreasing trends due to emission reductions during the first period but not the second. This suggests that the emission reduction measures had a relatively larger effect on wet deposition during the second period, at least for the sites with observations.

Trends of inorganic and organic aerosols and precursor gases in Europe: insights from the EURODELTA multi-model experiment over the 1990–2010 period

“…Consequently, a larger fraction of TNHx is in NH3 form, which deposits faster than NH4 + , leading to a positive retroaction in enhancing the downward trend of TNHx. Deposition plays a critical role in TNHx trends, and it has been noted that the observed decrease in wet deposition in the 1990s was largely driven by a couple of monitoring stations that experienced a sharp drop between 1995 and 1996 (Theobald et al, 2019) which the models fail to capture.…”

Trends of inorganic and organic aerosols and precursor gases in Europe: insights from the EURODELTA multi-model experiment over the 1990–2010 period

“…An error in primary particulate emission matter for Russia, north Africa and maritime areas for the period of 1991-1999 was identified at the end of the exercise. However, the effect of the error was estimated to be very limited (Theobald et al, 2019).…”

“…Emissions of SO 2 and NO 2 have largely declined in Europe over the recent decades (Fagerli and Aas, 2008;Tørseth et al, 2012;UNECE LRTAP, 2016). For SO 2 and NO 2 , emissions were reported to have declined by about 65 % and 31 %, respectively, between 1990 and 2009, whereas emissions of NH 3 were reported to have declined by about 29 %, although the emission changes exhibit high spatial variability within the European domain (Tørseth et al, 2012). NH 3 , which is emitted mainly from agricultural activities, is one of the key chemical species involved in the formation of secondary inorganic aerosol.…”

“…Past and future trends in the total PM concentration have recently received great attention thanks to the availability of long-term observational datasets and increased computational power available for long-term chemical transport model (CTM) simulations. Tørseth et al (2012) analyzed long-term air quality trends from the European Monitoring and Evaluation Programme (EMEP) during a period of 40 years. Their study showed a substantial reduction in ambient concentrations of sulfur species of about 70 %-90 % starting from 1980, well in line with emission reductions, and a reduction of about 23 % in NO 2 concentrations starting from the beginning of the 1990s.…”

Sensitivity of <i>CHIMERE</i> to changes in model resolution and chemistry over the northwestern Iberian Peninsula

“…In addition to this short-term 1 see Kukkonen et al (2012) for an overview of these models prediction system, several large research initiatives have been issued during the last two decades in order to assess the climatological properties of atmospheric composition, including the assessment of long-term tendencies resulting from emission reductions induced by the Convention on Long Range Transboundary Air Pollution (CLRTAP). The final aim of these efforts is to find model configurations, or ensembles thereof, that can be used as surrogates for real observations in order to assess whether emission reductions actually have lead, or would lead, to changes in the atmosphere's composition on climatological time-scales (Vautard et al, 2006;Jonson et al, 2006;Colette et al, 2011;Wilson et al, 2012;Banzhaf et al, 2015;Colette et al, 2017;Im et al, 2018b, a;Vivanco et al, 2018;Theobald et al, 2019).…”