The Jungfraujoch high-alpine research station (3454 m) as a background clean continental site for the measurement of aerosol parameters

Abstract

The first annual data set of climatically important aerosol parameters, measured at the Jungfraujoch (JFJ) high-alpine research station (3454 m, Switzerland) from an ongoing field campaign since July 1995, is presented. Analysis of diurnal variations in continuous measurements of the total and backward hemispheric scattering coefficients (8sSP, 8sBSP), the absorption coefficient (8sAP, from aethalometer data), condensation nuclei (CN) concentration, and epiphaniometer signal (related to surface area (S) concentration) established the diurnal period 0300 - 0900 as being representative of the free tropospheric background aerosol. The annual data set was then edited to omit (1) the period 0900 -0300 (i.e., 18 hours), taken to represent possible planetary boundary layer influenced conditions adn (2) in-cloud conditions using a cloud liquid-water monitor. The seasonal aerosol cycle exhibited a July maximum and a December minimum in most aerosol parameters. Typical monthly median values for the free troposphere exhibit the following seasonal maxima and minima, respectively: 8sSP (550 nm) 9a 16.1 and 0.43 x 10-6 m-1, 8sBSP (550 nm) 9a 2.10 and 0.09 x 10-6 m-1, 8sAP (550 nm) 9a 10.4 and 0.76 x 10-7 m-1 (9A 104 and 7.6 ng m-3 black carbon), CN concentrations 9a 670 and 280 cm-3, and epiphaniometer signal 9a 9.26 and 0.67 counts s-1 (S concentration 9A 24.1 and 1.7 8m m2 cm-3). Aerosol parameters were found to be comparable in magnitude to other NOAA baseline and regional stations and suggest that a clean continental designation for the JFJ site is applicable, when removing the planetary boundary layer influenced period.