New trajectory-driven aerosol and chemical process model Chemical and Aerosol Lagrangian Model (CALM)

摘要

A new Chemical and Aerosol Lagrangian Model (CALM) has been developed andtested. The model incorporates all central aerosol dynamical processes, fromnucleation, condensation, coagulation and deposition to cloud formation andin-cloud processing. The model is tested and evaluated against observationsperformed at the SMEAR II station located at Hyyti?l?(61° 51' N, 24° 17' E) over a time period of twoyears, 2000–2001. The model shows good agreement with measurementsthroughout most of the year, but fails in reproducing the aerosol propertiesduring the winter season, resulting in poor agreement between model andmeasurements especially during December–January. Nevertheless, through therest of the year both trends and magnitude of modal concentrations show goodagreement with observation, as do the monthly average size distributionproperties. The model is also shown to capture individual nucleation eventsto a certain degree. This indicates that nucleation largely is controlled bythe availability of nucleating material (as prescribed by the[H₂SO₄]), availability of condensing material (in this model 15%of primary reactions of monoterpenes (MT) are assumed to produce low volatilespecies) and the properties of the size distribution (more specifically, thecondensation sink). This is further demonstrated by the fact that the modelcaptures the annual trend in nuclei mode concentration. The model is alsoused, alongside sensitivity tests, to examine which processes dominate theaerosol size distribution physical properties. It is shown, in agreement withprevious studies, that nucleation governs the number concentration duringtransport from clean areas. It is also shown that primary number emissionsalmost exclusively govern the CN concentration when air from Central Europeis advected north over Scandinavia. We also show that biogenic emissions havea large influence on the amount of potential CCN observed over the borealregion, as shown by the agreement between observations and modeled resultsfor the receptor SMEAR II, Hyyti?l?, during the studiedperiod.