FORMATION AND THE PHYSICOCHEMICAL PROPERTIES OF THE TROPOSPHERIC AEROSOL

An evaluation of the long-term records of aerosol and meteorological parameters at the Meteorological Observatory of Hamburg reveals that particle production in the nucleation mode is stimulated by solar radiation and is enhanced by elevated SO, or NO, concentrations. While the particle number increases, their average sulfate or nitrate content per particle decreases with increasing sunshine. In the accumulation and coarse mode sulfate production takes place even at relative humidities above 80% but no nitrate production, while in the nucleation mode, nitrate production occurs at high humidities but only a weak sulfate production. The nitrate to sulfate ratio shows a winter maximum and a summer minimum in the course of the year and a long term increase over the past 6 years in both size ranges. The sulfate content of the Aitken particles shows a broad maximum in autumn. Coagulation causes a rapid mass transfer from the nucleation to the accumulation mode at high concentrations (> 100 cm-3) of large particles. In the long-term trend, the aerosol mass showed an increase between 1976 and 1986 and a decrease since then but the Dumber concentration of the large particles (0.1 less-than-or-equal-to r less-than-or-equal-to 1-mu-m) is still increasing. This aerosol fraction has the longest atmospheric residence time. The Aitken particle number has reduced since 1980 most probably caused by a reduction of the SO2 concentration. With respect to physico-chemical properties, the particle growth with relative humidity and the problem of internal or external mixing are discussed.