Fog scavenging of organic and inorganic aerosol in the Po Valley
Stefania GilardoniP. MassoliL. GiulianelliMatteo RinaldiMarco PaglioneFrancesca PolliniChristian LanconelliVanes PoluzziSamara CarboneRisto HillamoLynn M. RussellM. C. FacchiniS. Fuzzi
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Abstract. The interaction of aerosol with atmospheric water affects the processing and wet removal of atmospheric particles. Understanding such interaction is mandatory to improve model description of aerosol lifetime and ageing. We analyzed the aerosol–water interaction at high relative humidity during fog events in the Po Valley within the framework of the Agenzia Regionale per la Prevenzione e l'Ambiente (ARPA) – Emilia Romagna supersite project. For the first time in this area, the changes in particle chemical composition caused by fog are discussed along with changes in particle microphysics. During the experiment, 14 fog events were observed. The average mass scavenging efficiency was 70% for nitrate, 68% for ammonium, 61% for sulfate, 50% for organics, and 39% for black carbon. After fog formation, the interstitial aerosol was dominated by particles smaller than 200 nm Dva (vacuum aerodynamic diameter) and enriched in carbonaceous aerosol, mainly black carbon and water-insoluble organic aerosol. For each fog event, the size-segregated scavenging efficiency of nitrate and organic aerosol (OA) was calculated by comparing chemical species size distribution before and after fog formation. For both nitrate and OA, the size-segregated scavenging efficiency followed a sigmoidal curve, with values close to zero below 100 nm Dva and close to 1 above 700 nm Dva. OA was able to affect scavenging efficiency of nitrate in particles smaller than 300 nm Dva. A linear correlation between nitrate scavenging and particle hygroscopicity (κ) was observed, indicating that 44–51% of the variability of nitrate scavenging in smaller particles (below 300 nm Dva) was explained by changes in particle chemical composition. The size-segregated scavenging curves of OA followed those of nitrate, suggesting that organic scavenging was controlled by mixing with water-soluble species. In particular, functional group composition and OA elemental analysis indicated that more oxidized OA was scavenged more efficiently than less oxidized OA. Nevertheless, the small variability of organic functional group composition during the experiment did not allow us to discriminate the effect of different organic functionalities on OA scavenging.Keywords:
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Ammonium nitrate
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Owing to investigate the scavenging process of the loop scavenging two-cycle Diesel engine, some simplified scavenge tests have been proposed and reported. In their papers the relation between the results of simplified tests and characteristics of engine performance have been directly discussed. However, the mutual relation among those results, scavenge flow and gas exchange is not clear, hence we have difficulty of interpretation about the results of simplified tests.Therefore, we made an attempt to investigate the relation among some simplified tests, scavenge flow and scavenging efficiencies. The results obtained are as follows; 1) The effect of the piston movement in the pattern of scavenging pictures does not appear. That is, if the shapes and arrangements of scavenge ports are same, same scavenging pictures are obtained in the both cases of steady flow and dynamic scavenging. 2) Comparing the two unsatisfactory scavenging pictures which depend on the scavenge port arrangement, it was found that good scavenge could not expected in case of the scavenging pictures of middle tongue rather than that of wall tongues. 3) The part of relation between the results of simplified tests and scavenging efficiencies was cleared by setting up criteria in scavenging pictures.
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This paper reports the results of an investigation on the scavenging process in a model cylinder having a cross-scavenging system. The movement of the scavenge front in the cylinder and the short-circuiting of fresh charge were investigated by an electronic method. The profile of the scavenge front was made clear. The port arrangement investigated here gives a flat scavenge and an early short-circuiting occurs at the exhaust ports located near the scavenging ports. A poorly scavenging region exists above the exhaust ports.
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