Modelling of airborne pollen dispersion in the atmosphere in the Catalonia region, Spain: model description, emission scheme and evaluation of model performance for the case of Pinus

摘要

Pollination is a biologically-relevant process that affects the structure of ecosystems since pollen contributes to determinethe spatial distribution of plant species. It is thus of interest for mapping ecosystem services for policy support and decisionmaking to increase our knowledge of pollen grain behavior in the atmosphere (source, emission, processes involved duringtheir transport, etc.) at fine temporal and spatial scales. First simulations with the Barcelona Supercomputing CenterMONARCH dispersion model (known before as NMMB/BSC-CTM) of Pinus pollen in the atmosphere were performedduring a 5-day pollination event observed in Barcelona, Spain, between 27 – 31 March, 2015. MONARCH is an onlineatmospheric composition model that solves the life cycle of water vapor, gases and aerosols within a meteorological model.A new aerosol emission scheme for pollen grains has been implemented in the system. The emission scheme considerswind speed at 10 m, friction velocity, and temperature and specific humidity at 2 m as main drivers of the mobilization ofPinus pollen grains. The meteorological information is available for the emission scheme at each meteorologicalintegration time step. The spatial distribution of the pine species (P. halepensis, P. pinea) that pollinate from February toApril in Catalonia has been derived from the Cartography of habitats of Catalonia and the tree density was obtained fromthe Forest Inventory of Catalonia. A domain over north-east Spain at 9 km x 9 km horizontal resolution covering Cataloniais designed with 48 vertical layers. The initial and boundary meteorological conditions are derived from the fifth majorglobal ECMWF ReAnalysis (ERA-5). To evaluate the model performances, the simulations are compared (i) to groundbasedconcentration measurements performed with a Hirst collector in Barcelona downtown, and (ii) to vertically-resolvedmeasurements performed 4 km west of Barcelona downtown with a Micro Pulse Lidar (MPL). A method based on thelidar polarization capabilities was used to retrieve the contribution of the pollen to the total signal. The conversion fromoptical lidar-retrieved properties to concentration was optimized by minimizing the sum of the squared deviations betweenthe lidar-retrieved concentration at the first height and the true (Hirst) concentration measured at the ground. In terms ofsurface concentration, the simulation performs well during the center of the event with major underestimation at thebeginning. As far as the vertical distribution of airborne Pinus pollen is concerned, simulations reproduce well the shapeof the profiles but the intensity tends to be underestimated. Three major limitations are identified with the model runs: (1)the poorly known phenology emission function, (2) the temporal development of the convective planetary boundary layerin coastal areas, which directly affects the vertical structure of the pollen dispersion; (3) the development of the sea breezeand a proper representation of the sea coast line, that play a significant role on the skills of the meteorological mesoscalemodel.