The growth of atmospheric aerosol particles with relative humidity

Average particle growth of atmospheric aerosol particles due to water absorption are presented as a function of particle size and a variety of aerosol types. Aitken particles ( r < 0.1 μm) and large particles (0.1 ⩽ r ⩽ 1 μm) exhibit a similar growth type which can be described as smooth without any steps. The behaviour is very similar for continental and maritime aerosols and typical for mixed particles. Giant particles of continental origin also show similar behaviour while marine giant particles grow like sea salt. Particle growth is essentially determined by the chemical composition, however, in the real atmosphere particle growth due to changes in humidity and changes in chemical composition occur simultaneously because chemical equilibria depend on the amount of absorbed water. It has been found that at high humidity (> 80%) the acid content of aerosol samples is higher on the average as compared with lower humidities. Another important reciprocal effect is that the pH-value of particles changes due to the varing water amount. Possible consequences are discussed.