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Ion Chromatography Determination of Acid Components in Airborne Particles in Zagreb Air

Ion chromatography, as a separation technique, is the most widely used in analysis of liquid samples. With appropriate sample collection and preparation procedures it may be used in analysis of solid and vapour samples. In our investigation ion chromatography was used for acid content analysis (chlorides, nitrates, sulphates) in high-risk particle fraction (PM2.5 - particles with equivalent aerodynamic diameter less than 2.5 mm) in the ambient air. Acid aerosols are formed primarily from the oxidation of sulphur oxides, nitrogen oxides and hydrocarbons, originating primarily from combustion sources. They are mainly present in the high-risk particle fraction and penetrate deep into the alveolal region. The sampling site was located in the northern, residential part of Zagreb, at the distance of approximately 20 m from the road with moderate to high traffic density. The sampling was carried out continuously over the one-year period (21st March 1999 - 20th March 2000). Twenty four hour samples of high-risk particle fraction samples were collected by means of cellulose membrane filters (Millipore SSWP09025 or AAWP09025, pore size 0.8 mm) at he average sampling flow rate of 70 Lpm, from approximately 100 m3 of ambient air. The coarser particle fraction was removed from the air stream using inertial impactor. Filters were dried to constant humidity in a desiccator for 24-hour periods before and after sampling. Particle mass concentration was determined by gravimetric method. Samples were extracted from the filter media by use of an ultrasonic bath for one hour at 40 °C. Undisolved part was separated by centrifugation. For anion content measurement, Dionex DX-120 ion chromatograph equiped with suppressed conductivity detection Dionex AS14: 4mm Analytical Column + AG14: 4mm Guard Column were used. In order to check for possible background contamination, blank samples (unexposed filters) were used and processed simultaneously with the field samples. Results show that the mass concentration distributions of all investigated pollutants could be approximated to the lognormal distribution (p<0.001) with annual median values of 29.3 mgm-3 for PM2.5, 0.28 mgm-3 for chlorides, 1.99 mgm-3 for nitrates and 3.97mgm-3 for sulphates. Seasonal mass concentrations differ significantly for each pollutant. The overall anion content in high-risk particle fraction amounted to 22.3 %, sulphates dominating. Nitrate and sulphate content varied with season, while chloride content showed no seasonal dependence.

PM2; 5 high-risk particle fraction; chlorides; nitrates; sulphates

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