Seasonal changes in the chemical composition and mass closure of size resolved aerosol particles

Chemical composition and size distribution of atmospheric aerosol particles are controlled by the intensity and spatial distribution of their sources, transport and weather condition. These parameters and consequently the chemical composition and mass closure of the particles have temporal variation. The aim of this presentation is to discuss the seasonal variation of the size resolved chemical composition and mass closure of fine aerosol particles (d < 2 mu m). Fine atmospheric aerosol was sampled at K-puszta site under rural conditions in Central Hungary. The sampling was carried out by an electrical low-pressure impactor (ELPI), which fractionated fine particles (d < 1.7 mu m) in eight size ranges. Ammonium and sulphate concentrations have significant maximum in summer. Total carbon (TC) content of the fine particles is found to be important in all seasons. Except in summer, the average TC concentration exceeds that of sulphate. The water-soluble organic carbon concentration (WSOC) is found to be important during the year. The highest WSOC fraction of TC is measured in summer (70%). It should also be noted that in summer all water-soluble compounds (WSC) (including inorganic ions and WSOC) represent 50% (or more) of total fine mass, while in other seasons this value is less than 30%. During the year, the size distribution of sulphate is unimodal, while the size distributions of TC are dissimilar in different seasons. The size distribution of TC concentration is generally unimodal with maximum in the accumulation mode. However, in the ultra fine (bellow 0.1 mu m) size ranges non-negligible carbon concentration can also be measured, which can be the product of new particle formation. This phenomenon is much more intensive in summer, when the TC size distribution becomes bimodal. Further consequence of the important ultra-fine carbon mass is the, probably, high carbonaceous particle number concentration. WSOC gives important fraction of the TC in this size range, which may be important in cloud formation, especially in summer. From these data one can conclude that in summer the particles are more hygroscopic than in other periods of the year. The results on the hygroscopic behaviour of size resolved aerosol particles, sampled in summer, are presented in the conference by Imre et al.