Organics alter hygroscopic behavior of atmospheric particles

The optical and chemical properties of atmospheric particles and their ability to act as cloud condensation nuclei (CCN) depend strongly upon their affinity for water. Concurrent observations of particle chemical composition and water content from a continental nonurban (Grand Canyon) and an urban (Los Angeles) location have been analysed to determine whether the water content of atmospheric particles is influenced by the presence of organics. By comparing the observed water content with the water content expected to be associated with the inorganic fraction, it is found that the aggregate hygroscopic properties of inorganic particles are altered substantially when organics are also present. Furthermore, the alterations can be positive or negative. (from Authors)