This "19th Informal Conference on Photochemistry" will be the next in a long series of conferences that have attracted international groups of leading research workers in its field. The conferences have played an important role as media of exchange of information and ideas among scientists at the forefront of photochemical research. These biennial conferences attract atmospheric chemists because they are brought into contact with workers at the cutting edge of "pure" gas photochemistry. On the other hand, workers in general photochemistry are made aware of problems and research opportunities in atmospheric chemistry. The 19th Conference will have one full day of atmospheric chemistry papers.