Vertically resolved physico-chemical properties of atmospheric nanoparticles at the ARM Southern Great Plains Site

 

Authors

James Smith — University of California, Irvine
Haihan Chen — University of California Irvine
John Ortega — National Center for Atmospheric Research
James P Greenberg — National Center for Atmospheric Research
Jeffrey Robert Pierce — Colorado State University
Peter H McMurry — University of Minnesota

Category

General topics – Aerosols

Description

We report measurements of 10-20-nm-diameter particle number concentrations as a function of time and altitude from ground level to 1000 m above ground. The measurements were performed using a tethered balloon carrying two light-weight condensation particle counters that were set to two different particle cut-off diameters. Measurements were made during four days of the 2013 New Particle Formation Study at the ARM Southern Great Plains (SGP) site in Lamont, OK (April and May, 2013). Two flight days coincided with new particle formation (NPF) events. On those days we observed that 10-20-nm-diameter particles were generated aloft and were then rapidly mixed throughout the boundary layer. Given this fact, and assuming that the generated nanoparticles were internally mixed, we estimate the liquid water content of 10–100-nm-diameter particles using ground-based measurements of particle hygroscopicity obtained with a humidified tandem differential mobility analyzer and vertically-resolved relative humidity and temperature measured with a Raman lidar. Our analyses of these observations lead to the following conclusions regarding nanoparticles formed during NPF events at SGP: (1) Ground-based observations may not always accurately represent the timing, distribution, and physico-chemical conditions associated with the onset of NPF. (2) Once nanoparticles are formed, they are mixed throughout the boundary layer with time scales of less than an hour. (3) Nanoparticles typically contain up to 50% water by volume, and during conditions of high RH combined with high particle hygroscopicity, particles can be up to 90% water by volume. The implications of these conclusions on particle-phase chemistry and climate will be discussed.