Determining the Contribution of Measured New Particle Formation on Aerosol Size Distributions During the SEAC4RS Campaign

Wednesday, 17 December 2014
Brian S Meland, University of Denver, Denver, CO, United States, Duncan Axisa, NCAR, Boulder, CO, United States and James C Wilson, Univ Denver, Denver, CO, United States
The University of Denver Nucleation-Mode Aerosol Size Spectrometer (NMASS) was used to measure aerosol size distributions during 12 flights on board the Spec Learjet during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. The NMASS consists of 5 continuous flow CPCs operating in parallel which allows for the measurement of 5 channel size distributions covering size range of 4 to 60 nm with 1 Hz temporal resolution.

On-going new particle formation events, such as gas to particle conversion, can create particles with diameters of one to two nanometers. Through coagulation and condensation, these particles can grow to diameters sufficiently large as to act as cloud condensation nuclei. In-situ measurements of particles with the NMASS provide evidence for recent new particle formation since nanometer sized particles are converted rapidly by coagulation to detectable size ranges (diameters > 4 nm).

During SEAC4RS, strong evidence of new particle formation was seen in the lower, < 1.5 km, and the upper, 8-12 km , troposphere. At mid altitudes (2-7 km), much fewer NPF events were seen correlating strongly with a decrease in total measured particle concentrations. Evidence of NPF was seen in approximately 20% of all of our measurements during SEAC4RS, though over 90% of measurements near the tropopause were indicative of NPF. Forward trajectories of newly formed particles have been determined using NOAA’s Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) along with calculations of aerosol coagulation to determine the impact of these newly formed particles downwind of their sources.