Second meeting of the dry deposition working group

2024-04-11

SUMMARY

Svetlana Tsyro (MET Norway)
Presentation title: First experience of using ICP Forests observations for evaluation of CAMS models with respect to sodium deposition. On behalf of the team CAMS2_40 Task 4041

An intercomparison of six CAMS regional models (CHIMERE, DEHM, EMEP, LOTOS-EUROS, MOCAGE and SILAM) was conducted within the project “CAMS2_40 Regional Air Quality products, Task 4041 Deposition”. Results were furthermore compared to data from ICP Forests Level II sites as well as to data from EMEP measurement sites. The estimates of the different models were assessed for the year 2018 (seasonal pattern, spatial pattern and aggregated results). The model-model and model-measurement deviations were quantified for a range of substances, including wet and total deposition of sodium. Some of the results are show in the “AeroVal” interactive data explorer:
https://aeroval.met.no/pages/intercomp/?project=cams2_40_p2

Carmen Iacoban (INCDS)
Presentation title: Influence of plant material on the precision of determining mineral ions from precipitation (Cercetări pentru stabilirea influenţei materialului vegetal asupra preciziei determinării ionilor minerali din precipitaţii) (Barbu, I., Iacoban, C., Barbu, C., 1999, Bucovina forestiera)

The purpose of the organized experiment was to highlight the influence of the different type of plant material on some physical-chemical parameters and concentrations of the main cations in precipitation samples. Distilled water was used and put in contact, for different periods of time, with fresh different plant material, similar with that „washed” from the forest canopy by rainfall. The parameters analyzed were: pH, conductivity, and concentrations of Ca, Mg, K, Na and N-NH4. Analysing the significance of the differences (F test) for 7 parameters of precipitation samples it was found:

• For the factor time (4 variants), the parameters pH, conductivity and N-NH4 were sigificantlly influenced by the contact time. The influence on the concentrations of metal ions (Ca, Mg, K, Na) was insignificant, so the diffusion of these ions from the plant material and the dissolution of dry deposition was achived in the fisrt 3 days of contact.
• For the factor type of plant material (7 variants), the differences were statistically significant for all the parameters

Another analysis was performed in order to establish the influence of the quantity of plant material and contact time on conductivity, and concentrations of N-NH4, Ca, Mg, K and Na and to compare the values of these parameters with the detection limit and the mean annual concentartions registered in throughfall samples.

1. For small quantities (less than 1 g/l), no one of the analysed ions was significantly influenced by the presence of the plant material. The increase of concentrations determined in lab was below 10% from the annual mean value for each analysed ion. More than 95% of samples analysed in the period 1996-2000 were in this category.
2. For high quantities of litter (1-2g/l), concentrations of K and N-NH4 increased with 20-30% from the annual mean, while for conductivity, Ca, Mg and Na the increasing was of 5-20% from the annual mean in throughfall.
3. For very high quantities of litter (>5g/l), the increasing of concentration (for 3 and 30 days of contact of distilled water with the plant material) was of 20-80% from the annual concentration in throughfall.

Arne Verstraeten (INBO)

Presentation title: Effects of tree pollen on throughfall element fluxes in European forests (Verstraeten et al., 2023, Biog.)

During the spring, anemophilous forest trees disperse pollen in the atmosphere. Pollen is removed from the air through dry and wet deposition and ends up in throughfall (TF) samplers. The pollen mantle can dissolve in water, affecting TF element concentrations and measured depositions.

We analysed long-term data (6-29 years) from 61 ICP Forests Level II plots (12 countries) in relation to airborne pollen concentrations measured at 56 aerobiological monitoring stations in nearby cities (<100 km distance in flat areas, <75 km in mountains) for homogeneous Fagus, Quercus, Pinus and Picea stands. The TF fluxes of nitrate, ammonium, potassium, dissolved organic nitrogen and dissolved organic carbon during the main pollen season (MPS, arbitrary two months) were analysed in function of the Seasonal Pollen Integral (SPIn) for the dominant tree species. A quantitative estimate of the effects of pollen was made by subtracting the TF fluxes in the preceding and subsequent month from the TF fluxes during the MPS.

For Fagus, a masting genus showing high variation in pollen abundance, TF fluxes of all elements showed a significant positive relationship with SPIn, except nitrate, for which the relationship was negative. Fewer significant relationships were found for the other genera, partly explained by limited variability in SPIn. Overall, pollen contributed to TF fluxes mostly in Quercus > Fagus > Pinus > Picea stands, representing 4-10% of the annual TF flux of ammonium, potassium, dissolved organic nitrogen and dissolved organic carbon. On the other hand, pollen removes a small part of the annual TF nitrate fluxes.

The results from this inter-annual study at European scale were broadly confirmed by a laboratory experiment, but further study is needed to check the possible role of microorganisms.

Andreas Schmitz (LANUV)

Presentation title: K:Na ratios in wet and dry deposition

The “filtering approach” allows estimating the dry deposition (DD) of several substances from regular ICP Forests Level II deposition measurements. However, the accuracy of DD estimates from this approach for different substances and regions across Europe is not clear. Uncertainty arises from several factors, including the assumption of similar substance ratios in DD and wet deposition (WD).

In this study, the accuracy of the filtering approach for the DD of K⁺ was tested based on 6 years of modelled DD and measured WD at the EMEP site “Melpitz” in rural Germany. DD modelling was conduced based on daily K⁺ and Na⁺ air concentrations in PM_2.5 and PM₁₀ measured at the Melpitz site in combination with a state-of-the-art particle DD model.

Results indicate that the filtering approach underestimates the DD of K⁺ by a factor of 1.37 compared to the modelled DD to a "virtual" conifer indicator forest. Uncertainty arises from the DD model and the potential presence of super-coarse particles not measured by the PM₁₀ sampler. Excluding periods potentially affatected by super-coarse dust from the agricultural fields surrounding the measurements site increased the correction factor to 1.77. Further research is required to get a more comprehensive perspective on the accuracy of the filtering approach across Europe.