New particle formation in the continental boundary layer: Meteorological and gas phase parameter influence

New particle formation in the polluted continental boundary layer was studi ed, based on 1.5-year observations of the particle size distribution, meteo rological and gas phase parameters. Events of new particle formation involv ing significant ultrafine particle number concentrations (> 10(4) cm(-3) in the size range 3-11 nm) were observed on 20 % of all days, pointing out th at a frequent particle production from gaseous precursors can occur despite the relatively high pre-existing particle surface area in the area of inve stigation. The maximum in the observed particle size distributions was most ly above 3 nm, suggesting the actual particle nucleation to take place upwi nd of the measurement site. A particle growth analysis yielded 2.3 +/- 1.4 h as an upper limit of the time for the particles to grow from the critical cluster size till the observation of the peak in ultrafine number concentr ation. On 80 % of the significant events of new particle formation (though not on all), SO2 concentrations increased considerably (by an average facto r of 7), most likely by entrainment from aloft. Particle surface area was, on average, higher on event days compared to non-event days, indicating onl y a weak competition between condensation onto the pre-existing particle su rface area and the new particle formation process. The highest statistical correlation was found between the events of new particle formation and sola r radiation, indicating a high degree of meteorological control.