Particle size distribution expressed as number concentration per size bin. This dataset is associated with the following publications: Pillai, P., V. Aneja, J. Walker , and A. Khlystov. Observation and Analysis of Particle Nucleation at a Forest Site in the Southeast U.S.. Atmospheric Pollution Research. Turkish National Committee for Air Pollution Research and Control, Izmir, TURKEY, 4(2): 72-93, (2013). Yu, F., and J. Walker. Spring and summer contrast in new particle formation over nine forest areas in North America. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, GERMANY, 15(24): 13993-14003, (2105). Sullivan, R., P. Crippa, A.G. Hallar, L. Clarisse, W.R. Leaitch, J. Walker, A. Khlystov, and S.C. Pryor. Using satellite-based measurements to explore spatiotemporal scales and variability of drivers of new particle formation. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. American Geophysical Union, Washington, DC, USA, 121(20): 12217-12235, (2016).