Observation of number concentrations of atmospheric aerosols and analysis of nanoparticle behavior at an urban background area in Japan

To clarify nanoparticle behavior, observations of atmospheric aerosols, weather, and trace gases were carried out for about 1 month in summer and in winter at a region apart from major emission sources in Nagakute, Japan. The relation of nanoparticles with pollutants was clarified, and the potential of photochemical nucleation was pointed out based on the relation with meteorology and trace gas concentrations. The variation in particle size depends on the concentration of materials to be used in coagulation, condensation, and evaporation processes, except for photochemical nucleation. In winter, a minimum peak diameter of particle size distribution of about 40 nm was observed during the morning rush, and the growth rate of particle size during the morning was 7.6 nm h−1. On the other hand, the minimum size was recorded in the daytime in summer, and a large growth rate of 14.7 nm h−1 was obtained in the evening. The particle growth due to coagulation and condensation was thought to start with the morning rush and to continue until the next early morning in winter. The coagulation and condensation materials promoting particle growth were produced during the daytime, and a decrease in ambient temperature might contribute to particle growth during the night. In addition, a continuous particle growth was seen under a stable high atmospheric pressure for a few days. The average cyclic period of the particle growth and shrinkage of 81.9 h, which was calculated as a result of a Fourier analysis, was observed, and good correspondence was shown with the variation in atmospheric air pressure. The average growth rate during the time periods was 59.5 nm day−1 in winter and 103.3 nm day−1 in summer. The reason for the high value of the average growth in summer was thought to be the large amount of the materials produced which were used for particle growth through coagulation and condensation processes.