The growth of nanometer-size particles in the lower troposphere

Abstract

This chapter investigates the way airborne particles grow to the upper end of the Aitken mode, which is where particles may act as cloud condensation nuclei (CCN). To study the problem, it constructs a model that simulates the particle condensational growth under prescribed ambient conditions. Condensing species include water, sulfuric acid, ammonia, and nitric and hydrochloric acid. The thermodynamic part of the model, needed for calculating the condensational fluxes of various species between the gas and particulate phases, is based on the work of Potukuchi and Wexler. Coagulation that may be important for nuclei growth in the upper-free troposphere is not considered. In addition to inorganic acids and ammonia, the role of organic vapors in affecting the secondary particle growth is discussed. With this regard, it analyzes some experimental results obtained from the Finnish Arctic atmosphere. The growth of airborne nuclei was studied under conditions typical of the lower troposphere. The model simulations in the chapter suggest that pure sulfuric acid-water-ammonia condensation is rather slow, and as such unlikely to be able to produce CCN-size particles from nuclei formed in the lower troposphere. Nitric or hydrochloric acid together with ammonia may substantially accelerate nuclei growth in continental aerosol systems, whereas in marine locations these compounds probably are of minor importance. Organics have a potential to assist secondary CCN productions both in continental and marine environments.