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Presentation RSE 14002126

Atmospheric modeling reconstruction of ammonia in the Po Valley


PM2014 - VI Convegno sul particolato atmosferico 20-23 , Maggio-2014.

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V. Capiaghi (Politecnico di Milano), G. Pirovano (RSE SpA) , C. Colombi (ARPA Lombardia), G. Lonati (Politecnico di Milano), G. Riva (RSE SpA) , A. Toppetti (RSE SpA), V.Gianelle (ARPA Lombardia), A. Balzarini (RSE SpA)

CLIMATIZZAZIONE 2014 - Utilizzazione del calore solare e ambientale per la climatizzazione

Atmospheric particulate matter is produced by the contribution of different source categories, like road transport, domestic heating and agriculture, through ammonia emissions. The latter represents one of the main sources affecting the Po valley, that is often characterized by air quality exceedances. Ammonia reacts with other compounds, like sulphur and nitrogen oxides, mainly emitted by road transport and other combustion processes related to energy consumption. A reliable reproduction of the atmospheric processes involving ammonia represents an essential prerequisite in order to perform more robust evaluation of emission reduction scenarios, also including energy policies.

The CAMx chemical transport model (CTM) has been applied over the Po Valley (Northern Italy) to investigate the spatial and temporal pattern of ammonia, the gas phase precursor of ammonium particulate. Model results have been compared with systematic ammonia measurements of the Air Quality Network. CAMx proved to be skilful in reproducing the temporal evolution of ammonia concentration at receptors located in the most emitting areas (BIAS: -35%, +27%), while it underestimated ammonia levels in urban and remote areas. Nevertheless, Particulate Matter (PM) concentration has been correctly reproduced at most sites, showing BIAS lower than 20% for PM10 and less than 13% for PM2.5.

Model results suggest that the annual emission burden of ammonia is correctly quantified. Conversely, the underestimation taking place outside the high emission areas is probably related to:

1) an incorrect hourly modulation profile of ammonia emissions;
2) a poor reconstruction of the Planetary Boundary Layer (PBL);
3) an overestimation of dry deposition. All these effects contribute to dampen the effect of ammonia transport at basin scale. Conversely, the good performance in reproducing the PM concentration suggests that those effects are less relevant for secondary pollutants, the main fraction of PM in the Po Valley during these episodes.

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