Research on aerosol sources and chemical composition: Past, current and emerging issues

In spite of considerable progresses in recent years, a quantitative and predictive understanding of atmospheric aerosol sources, chemical composition, transformation processes and environmental effects is still rather limited, and therefore represents a major research challenge in atmospheric science. This review begins with a historical perspective on the scientific questions regarding atmospheric aerosols over the past centuries, followed by a description of the distribution, sources, transformation processes, and chemical and physical properties as they are currently understood. The major open questions and suggestions for future research priorities are outlined to narrow the gap between the present understanding of the contribution of both anthropogenic and biogenic aerosols to radiative forcing resulting from the spatial non-uniformity, intermittency of sources, unresolved composition and reactivity.