An approach to investigate new particle formation in the vertical direction on the basis of high time-resolution measurements at ground level and sea level

Abstract:

In this study, we investigated new particle formation (NPF) in the vertical direction using high time-resolution (1 s) measurements made by Fast Mobility Particle Sizers at ground level and at sea level. The coefficient of variation (CV), i.e., the ratio of standard deviation to mean value for <100-nm particle number concentration (N₁₀₀) in every 30 s, is introduced as a metric to distinguish horizontal and vertical transport of atmospheric particles. We first examined the CV metric using the data collected at a semi-urban site in Toronto during the summer of 2007. The 50^th and 95^th percentiles of CVs associated with horizontal transport were 1-13 times smaller than those during strong vertical transport. We then compared the N₁₀₀, GMD₅₅ (geometric mean diameter of <55-nm particles) and GMD₁₀₀ corresponding to the 0-5^th percentiles of CVs with those corresponding to the 95-100^thpercentiles of CVs in five NPF events (Fig. 1). The comparative results are discussed in terms of different formation and growth rates in the vertical direction. The similar analysis was also conducted in various marine atmospheres. We found that the CV metric can improve our understanding of NPF in the vertical direction.

Fig. 1 Time series of N100, GMD55, GMD100 corresponding to 95-100th percentile (left panel) and 0-5th percentile of CVs (right panel) for N100 in five NPF events (Case 5-9).