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 measurements of aerosol number size distributions, relevant gaseous components including H₂SO₄ and OH, and meteorological parameters. Measurements were conducted at Hohenpeissenberg, a rural continental mountain site in southern Germany. The event was observed under intense solar radiation, with total particle number concentrations increasing from 6000 to 25000 cm^-3 within one hour, and ultrafine particles (3-11 nm) accounting for more than 50% of total number. Observed OH and H₂SO₄ concentrations reached maximum levels around 10⁷ cm^-3. A lower limit of the particle nucleation rate was estimated to be 3 cm^-3·s^-1, consistent with present models of ternary nucleation involving the H₂SO₄-H₂O-NH₃ system. Roughly 80 % of the subsequent drop in ultrafine mode particle number concentration could be explained by coagulation. The observed particle growth rate of 2.1 ± 0.1 nm/h was largely attributed to the condensation of measured H₂SO₄, assuming neutralization by ammonia.