Aerosol climatology and planetary boundary influence at the Jungfraujoch analyzed by synoptic weather types
Fourteen years of meteorological parameters, aerosol variables (absorption and scattering coefficients, aerosol number concentration) and trace gases (CO, NOx, SO2) measured at the Jungfraujoch (JFJ, 3580m a.s.l.) have been analyzed as a function of different synoptic weather types. The Sch¨ uepp synoptic weather type of the Alps (SYNALP) classification from the AlpineWeather Statistics (AWS) was used to define the synoptic meteorology over the whole Swiss region. The seasonal contribution of each syn- optic weather type to the aerosol concentration was deduced from the aerosol annual cycles while the planetary bound- ary layer (PBL) influence was estimated by means of the diurnal cycles. Since aerosols are scavenged by precipita- tion, the diurnal cycle of the CO concentration was also used to identify polluted air masses. SO2 and NOx concentra- tions were used as precursor tracers for new particle forma- tion and growth, respectively. The aerosol optical parame- ters and number concentration showelevated loadings during advective weather types during the December–March period and for the convective anticyclonic and convective indiffer- ent weather types during the April–September period. This study confirms the consensus view that the JFJ is mainly in- fluenced by the free troposphere during winter and by injec- tion of air parcels from the PBL during summer. A more detailed picture is, however, drawn where the JFJ is com- pletely influenced by free tropospheric air masses in winter during advective weather types and largely influenced by the PBL also during the night in summer during the subsidence weather type. Between these two extreme situations, the PBL influence at the JFJ depends on both the time of year and the synoptic weather type. The fraction of PBL air transported to the JFJ was estimated by the relative increase of the specific humidity and CO.