An Improved Criterion for New Particle Formation in Diverse Environments

Chongai Kuang Brookhaven National Laboratory
Ilona Riipinen Carnegie Mellon University
Sanna-Liisa Sihto University of Helsinki
Markku Kulmala University of Helsinki
Alon McCormick University of Minnesota
Peter McMurry University of Minnesota

Category: Modeling

Working Group: Aerosol Life Cycle

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Histogram of measured Lg values associated with 77 new particle formation (NPF) events and 19 non-events from the MILAGRO (Tecamac), ANARChE (Atlanta), Boulder, QUEST II (Hyytiälä), QUEST IV (Hyytiälä), and EUCAARI (Hyytiälä) measurement campaigns. The dimensionless parameter Lg, characterizing the ratio of the particle scavenging loss rate to the particle growth rate, exclusively determines whether or not NPF can occur on a particular day. A boundary value of Lg = 0.7 separates NPF events and non-events, with values of Lg ranging from 0.0075–0.66 for NPF events and from 0.76–9.4 for non-events.

A dimensionless theory for new particle formation (NPF) was developed, using an aerosol population balance model incorporating recent developments in nucleation rates and measured particle growth rates. Based on this theoretical analysis, it was shown that a dimensionless parameter Lg, characterizing the ratio of the particle scavenging loss rate to the particle growth rate, exclusively determined whether or not NPF would occur on a particular day. This parameter determines the probability that a nucleated particle will grow to a detectable size before being lost by coagulation with the pre-existing aerosol. Cluster-cluster coagulation was shown to contribute negligibly to this survival probability under conditions pertinent to the atmosphere. Data acquired during intensive measurement campaigns in Tecamac (MILAGRO), Atlanta (ANARChE), Boulder, and Hyytiälä (QUEST II, QUEST IV, and EUCAARI) were used to test the validity of Lg as an NPF criterion. Measurements included aerosol size distributions down to 3 nm and gas-phase sulfuric acid concentrations. The model was applied to 77 NPF events and 19 non-events (characterized by growth of pre-existing aerosol without NPF) measured in diverse environments with broad ranges in sulfuric acid concentrations, ultrafine number concentrations, aerosol surface areas, and particle growth rates (nearly two orders of magnitude). Across this diverse data set, a nominal value of Lg = 0.7 was found to determine the boundary for the occurrence of NPF, with NPF occurring when Lg < 0.7 and being suppressed when Lg > 0.7. Moreover, nearly 45% of measured Lg values associated with NPF fell in the relatively narrow range of 0.1 < Lg < 0.3.

This poster will be displayed at ASR Science Team Meeting.