Nucleation events in the continental boundary layer: Influence of physical and meteorological parameters

[摘要] The relationship between nucleation events and numerous physical andmeteorological parameters was analysed using data collected at the Stationfor Measuring Forest Ecosystem-Atmosphere Relations (SMEAR II) in Hyytiälä, Finland. To do this, measurements of solar radiation(ultraviolet [UV], global, photosynthetically active radiation [PAR], net,reflected global radiation and reflected PAR), gas concentrations, temperature, humidity, wind direction, horizontal and vertical wind speed,horizontal and vertical wind variances and particle concentrations were collected over a 4 year period. For the year 1999 a detailedanalysis of data were completed by examining parameters in order to determine the physical andmeteorological conditions favourable to the formation of new particles. A comparison of different wavelength bands during the bursts of new particlesled to the suggestion, that UV-A solar radiation seems to be the most probable radiation band concerning the photochemical reactions involved inthe production of condensable vapours. Furthermore a high correlation betweenthe daily curves of UV-A irradiance and the concentration of 3 - 5 nm particles was found throughout the year and examples will be given for twodays. During the whole year the concentration of H₂O is very low at timesnucleation occurs compared to the average of the corresponding month. Especially in June and July many non-event days with high solarirradiance show high amounts of water molecules. To combine these results a"nucleation parameter" was calculated for the year 1999, by dividing UV-A solar radiationby the concentration of H₂O and temperature. Throughout the year nearlyall nucleation event days reach a value of the "nucleation parameter" of atleast 5.4 x 10^-25 W m molecules^-1 K^-1. Non-event days with high values (> 2.7 x10^-25 W m molecules^-1 K^-1) are mostly accompanied by high concentrations of existing particles.

[学科分类] 大气科学