One year boundary layer aerosol size distribution data from five nordic background stations

[摘要] Size distribution measurements performed at five different stations have been investigatedduring a one-year period between 01 June 2000 and 31 May 2001 with focus on diurnal,seasonal and geographical differences of size distribution properties. The stations involvedcover a large geographical area ranging from the Finnish Lapland (67º N) down to southernSweden (56º N) in the order Värriö, Pallas, Hyytiälä, Aspvreten andVavihill. The shape of the size distribution is typically bimodal during winter with a larger fraction ofaccumulation mode particles compared to the other seasons. Highest Aitken modeconcentration is found during summer and spring during the year of study. The maximum of nucleation events occur during the spring months at all stations. Nucleationevents occur during other months as well, although not as frequently. Large differences were found between different categories of stations. Northerly locatedstations such as Pallas and Värriö presented well-separated Aitken and accumulation modes,while the two modes often overlap significantly at the two southernmost stations Vavihill andAspvreten.

A method to cluster trajectories was used to analyse the impact of long-range transport on theobserved aerosol properties. Clusters of trajectories arriving from the continent were clearlyassociated with size distributions shifted towards the accumulation mode. This feature wasmore pronounced the further south the station was located. Marine- or Arctic-type clusterswere associated with large variability in the nuclei size ranges.

A quasi-lagrangian approach was used to investigate transport related changes in the aerosolproperties. Typically, an increase in especially Aitken mode concentrations was observedwhen advection from the north occurs, i.e. allowing more continental influence on the aerosolwhen comparing the different measurement sites. When trajectory clusters arrive to thestations from SW, a gradual decrease in number concentration is experienced in all modes aslatitude of measurement site increases.

[学科分类] 大气科学