Four storms with sub-events: Sampling and analysis

Analysis of ion concentration of samples taken sequentially during a storm event is important in order to reveal the relation between the atmospheric conditions and ion concentrations in each sub-event. This study presents the interrelationship among the chemical composition parameters and atmospheric variables for four storm events that were sampled in İstanbul during a) January 21–23, 2004 b) November 9–11, 2003 c) February 12–13, 2004 and d) October 27–28, 2003. These events lasted 53.3, 47.9, 27.5 and 13.2 h and the number of collected samples for each event was 22, 14, 7 and 4, in order. Generally values of pH and concentrations of ions in the first sub-events for all four cases were found higher than those of the other sub-event samples taken in sequence owing to the strong initial washout of the atmosphere by raindrops. Precipitation events a and c include rain and snow together where precipitation started as rain and continued as snow after 16th and 3rd sub-events. Higher concentration of ions in the snow in comparison with that of rain sub-events samples can be explained by more efficient below cloud scavenging of atmospheric constituents, especially aerosol particles, by snowflakes. In general, all of the ions sampled in the sub-events for four storms have variability similar to each other, with high correlation coefficient among themselves. Cl− and SO42− were found to be the dominant ions in average overall sub-events. Calculated NSS concentration values of ions indicated that the main source of SO42− was industrial and domestic emissions, most of the Ca2+ and K+ came from soil, nearly half of the Mg2+ and all of the Cl− originated from sea.