Evolution of newly formed aerosol particles in the continental boundary layer: A case study including OH and H2SO4 measurements

An event of new particle formation is presented, based on simultaneous meas urements of aerosol number size distributions, relevant gaseous components including H2SO4 and OH, and meteorological parameters. Measurements were co nducted at Hohenpeissenberg, a rural continental mountain site in southern Germany. The event was observed under intense solar radiation, with total p article number concentrations increasing from 6000 to 25000 cm(-3) within o ne hour, and ultrafine particles (3-11 nm) accounting for more than 50 % of total number. Observed OH and H2SO4 concentrations reached maximum levels around 10(7) cm(-3) A lower limit of the particle nucleation rate was estim ated to be 3 cm(-3) s(-1) consistent with present models of ternary nucleat ion involving the H2SO4-H2O-NH3 system. Roughly 80 % of the subsequent drop in ultrafine mode particle number concentration could be explained by coag ulation. The observed particle growth rate of 2.1 +/- 0.1 nm/h was largely attributed to the condensation of measured H2SO4, assuming neutralization b y ammonia.