Applying WRF-CMAQ models for assessment of sulphur and nitrogen deposition in Bulgaria for the years 2016 and 2017

Abstract

Wet, dry and total depositions of sulphur (S) and nitrogen (N) in Bulgaria are simulated on an annual and seasonal basis for the years 2016 and 2017 using WRF-CMAQ (9 km grid resolution). The mean annual values for wet depositions are about 1,300 kg.km -2 , the dry depositions are slightly lower for S and significantly lower for N (180 kg.km -2 ). The highest modelled wet depositions are in the western and south-western parts of the country, the highest dry depositions -in the northern and eastern parts. The comparison for the wet depositions at three sites with precipitation chemistry data indicates overestimation. A precipitation bias adjustment applied to the modelled depositions results in decrease of the normalised mean bias by a factor of 3. Comparison to modelled deposition data from literature for this region of the country is also provided.

Sulfur and Nitrogen Depositions in BULGARIA—Model Results and Observations

“…The method involves linear correction of model wet depositions by the ratio of the observed to estimated precipitation. In previous studies, [25,29] it was shown that the PBA approach led to improvement of monthly wet depositions in Bulgaria when comparing the model to observed values at single sites. Sensitivity tests on the effect of PBA on monthly wet depositions in Bulgaria suggested a decrease in annual wet depositions by about 25-30%, [31].…”

“…One of the reasons for this was the difference in the amount of accumulated precipitations for the studied period, with values at Ahtopol lower by more than 20% compared to values in Sofia. The number of days with precipitation in Ahtopol was also less (16) than in Sofia (25), suggesting that the removal of pollutants in Sofia was mainly through the wet deposition. Higher dry depositions of sulfur in Ahtopol in summer months (June to August) could be linked also to influence from the industrial plant "Lukoil Neftochim" Burgas, the largest refinery in the Balkans, located at about 60 km northwards.…”

“…Preliminary analysis of BgCWFS wet depositions [25,29] suggested model overestimation due to overestimation of precipitation amounts. Thus, a precipitation bias adjustment (PBA) approach was applied for wet deposition calculations following [46].…”

“…The protected areas (more than 41% of the national territory) are one of the largest in Europe [23]. On the other hand, South-East Europe and the Balkans were indicated as hot-spots for sulfur dioxide and sulfur wet depositions in several modeling studies [12,15,24,25]. The annual trend of total S, OXN, and RDN depositions in Bulgaria had small variability during 2015-2019, compared to a decreasing trend for the previous five years, as indicated by model estimates in [26].…”

“…However, chemical analysis of wet and dry atmospheric samples was carried out only at a few locations during field experiments [28][29][30]. On the modeling aspect, it is worth noting that NIMH recently started the estimation of atmospheric deposition for the country based on its operationally running CTM-the Bulgarian Chemical Weather Forecasting system (BgCWFS) [25,29,31]. Another modeling system that performs simulations for air pollutants, acidification, and eutrophication compounds over Europe on a routine basis was developed at the EMEP Meteorological Synthesizing Centre-West, the EMEP-MSC-W model [32], further denoted as EMEP-CTM.…”