Abstract：Distribution and variation characteristics of atmospheric particle number concentration in typical weather conditions were analyzed, by using 0.25~32μm particulate matter monitoring data with meteorological parameters and scattered extinction coefficient of the same period between March 2013 to December 2014 in Xi’an of China. The results indicated that mean atmospheric particle number concentrations were 206.27 cm-3. Among them, the particle which size less than 1μm accounted for over 99%. The highest particle number concentrations was observed in winter which was 267.66 cm-3, and followed by autumn, summer and spring, which were 231.31, 141.82 and 135.77 cm-3, respectively. The number concentration value was the lowest around 6PM throughout the four seasons, which were higher in night than in the day time. However, the concentration differences between the day and night were the smallest in summer and the highest in autumn. The Pearson correlation coefficients were respectively 0.756, 0.702, 0.411 and 0.377 between the scattered extinction coefficient and the particle number concentrations in the spring, summer, autumn, and winter. The particle number concentrations first increased and then decreased before and after dust and haze events. The particle number concentrations were relatively low in the hot and dry days. Rainfall removed particles significantly, but the particle number concentrations increased rapidly after the rain.
